Jorge Costa | ISCTE - University Institute of Lisbon (ISCTE-IUL) (original) (raw)

Journal Papers by Jorge Costa

Research paper thumbnail of Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band

Vaquero, Á.F.; Pino, M.R.; Arrebola, M.; Matos, S.A.; Costa, J.R.; Fernandes, C.A. Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band. Sensors 2021, 21, 422., Jan 2001

A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region... more A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region of the antenna in the Ka-band. The antenna is designed to focus the radiated field at a certain point using a central feeding configuration. The number of feeds is increased to create as many focusing spots as feeds. The feeds are placed along an arc defined in the principal planes of the transmitarray, radiating independent near-field spots and providing a solution with a wide-angle spot scanning without an antenna displacement and a high isolation between feeds. To validate this concept, a transmitarray based on dielectric-only cells is designed and simulated under full-wave conditions. Then, this design is manufactured using a 3D printing technique, and the prototype is measured in a planar acquisition range. Measurements are performed for different feed positions in order to validate the multi-focusing capability of the antenna. Measurements and simulations show a high agreement and validate the proposed design technique.

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Research paper thumbnail of Bessel Beam Generation Using Dielectric Planar Lenses at Millimeter Frequencies

Á. F. Vaquero, M. R. Pino, M. Arrebola, S. A. Matos, J. R. Costa and C. A. Fernandes, "Bessel Beam Generation Using Dielectric Planar Lenses at Millimeter Frequencies," in IEEE Access, vol. 8, pp. 216185-216196, 2020, Dec 2020

In this work a dielectric planar lens is proposed to generate a Bessel beam. The lens works at Ka... more In this work a dielectric planar lens is proposed to generate a Bessel beam. The lens works at Ka-band and produces a non-diffraction range within the Fresnel region of the antenna. The methodology to design the aperture antenna at millimetre or microwave frequencies is presented. It is applied to a dielectric planar lens made up of cells that shapes the radiated near-field by adjusting the unit cell response. An approach based on a second order polynomial is proposed to consider the angular dependence of the phase-shift response of the cell in the designing process. In order to implement the lens physically, two novel cells, based on rectangular and hexagonal prisms, are proposed, and their performance is compared. The cells ensure the index dielectric media variation using airgaps to control the overall density of the material. After fully characterizing the cells, a design is carried out for the two proposed type of cells. The requirement for the Bessel beam is a depth-of-field of 650 mm at 28 GHz. After evaluating the design in a full-wave simulation, both prototypes were manufactured using a 3-D printing technique. Finally, the prototypes were measured in a planar acquisition range to evaluate the performances of the Bessel beam. Both lenses show a good agreement between simulations and measurements, obtaining promising results in the Bessel beam generation by index-graded dielectric lenses at Ka-band. INDEX TERMS Dielectric lenses, Bessel beams, near-field focusing.

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Research paper thumbnail of Applying Massively Parallel Computing to Multiscale Ka Dual-Band Transmit-Array Analysis Using FETI-2LM

A. Barka, S. A. Matos, J. R. Costa, C. A. Fernandes and H. Chreim, "Applying Massively Parallel Computing to Multiscale Ka Dual-Band Transmit-Array Analysis Using FETI-2LM," in IEEE Journal on Multiscale and Multiphysics Computational Techniques, vol. 5, pp. 235-244, 2020, Nov 2020

Transmit-arrays (TAs) are a popular cost-effective solution for high-gain antennas at millimeter ... more Transmit-arrays (TAs) are a popular cost-effective solution for high-gain antennas at millimeter waves. The design of these antennas relies on the fine tuning of the subwavelength unit cells that compose the aperture. The intricacy of the unit cells increases as new features are implemented, such as dual-band operation and wide-angle beam steering, making this antenna even more computationally challenging. In this article, a high-gain (25 dBi @ 20 GHz and 28 dBi @ 30 GHz) multiscale Ka dual-band TA for beam-steering applications is analyzed using a massively parallel implementation on multicores clusters of the finite element tearing and interconnecting method, with a two Lagrange multiplier (FETI-2LM) technique. The main contribution of this article is the implementation of 3-D nonperiodic grids with subdomains of different scales, that is suitable for proper modeling of different regions of the antenna (horn feed, lens cells, and air region). An automatic batch file procedure is proposed for the TA meshing, allowing the limited set of constitutive unit cells of the TA to be meshed separately. Additionally, we are using a block-Krylov strategy to efficiently capture the TA beam-steering capability, without restarting from scratch the interface problem for each feed position. Since other finite element method results were not accessible due the size of the problem, the FETI-2LM numerical results provided in this article are compared with other multilevel fast multipole methods and transmission line modeling method of CST Microwave Studio solvers, as well as with the measured results of the corresponding Ka dual-band prototype. The computational infrastructure has been used only a fraction of its capacity. Therefore , a much higher gain design (40 dBi) can be assessed, opening a new realm of applicability of TAs in the space segment usually occupied by reflector-based solutions. Fig. 1. TA beam-steering antenna concept implemented in [2] for dual-band operation. Focal distance between the horn and the lens F = 100 mm, length along the X-axis D ax = 196 mm, and width along the Y-axis D ay = 147 mm. Index Terms-Domain decomposition, finite element method (FEM), finite element tearing and interconnecting (FETI), GID preprocessor, Ka-band transmit-array (TA), Krylov spaces.

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Research paper thumbnail of Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment

Savazzi, M.; Abedi, S.; Ištuk, N.; Joachimowicz, N.; Roussel, H.; Porter, E.; O’Halloran, M.; Costa, J.R.; Fernandes, C.A.; Felício, J.M.; Conceição, R.C. Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment. Sensors 2020, 20, 4968., 2020

We produced an anatomically and dielectrically realistic phantom of the axillary region to enable... more We produced an anatomically and dielectrically realistic phantom of the axillary region to enable the experimental assessment of Axillary Lymph Node (ALN) imaging using microwave imaging technology. We segmented a thoracic Computed Tomography (CT) scan and created a computer-aided designed file containing the anatomical configuration of the axillary region. The phantom comprises five 3D-printed parts representing the main tissues of interest of the axillary region for the purpose of microwave imaging: fat, muscle, bone, ALNs, and lung. The phantom allows the experimental assessment of multiple anatomical configurations, by including ALNs of different size, shape, and number in several locations. Except for the bone mimicking organ, which is made of solid conductive polymer, we 3D-printed cavities to represent the fat, muscle, ALN, and lung and filled them with appropriate tissue-mimicking liquids. Existing studies about complex permittivity of ALNs have reported limitations. To address these, we measured the complex permittivity of both human and animal lymph nodes using the standard open-ended coaxial-probe technique, over the 0.5 GHz-8.5 GHz frequency band, thus extending current knowledge on dielectric properties of ALNs. Lastly, we numerically evaluated the effect of the polymer which constitutes the cavities of the phantom and compared it to the realistic axillary region. The results showed a maximum difference of 7 dB at 4 GHz in the electric field magnitude coupled to the tissues and a maximum of 10 dB difference in the ALN response. Our results showed that the phantom is a good representation of the axillary region and a viable tool for pre-clinical assessment of microwave imaging technology.

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Research paper thumbnail of Communication Equivalent Circuit Modeling to Design a Dual-Band Dual Linear-to-Circular Polarizer Surface

P. Naseri, J. R. Costa, S. A. Matos, C. A. Fernandes and S. V. Hum, "Equivalent Circuit Modeling to Design a Dual-Band Dual Linear-to-Circular Polarizer Surface," in IEEE Transactions on Antennas and Propagation, vol. 68, no. 7, pp. 5730-5735, July 2020., 2020

The working principle of a thin dual-band dual-linear to circular polarizer is presented here. Th... more The working principle of a thin dual-band dual-linear to circular polarizer is presented here. This polarizer not only converts incident linearly polarized (LP) waves to circularly polarized (CP) waves in two frequency bands, but it also reverses the handedness of each signal. The electromagnetic behavior of the cell is carefully analyzed and two equivalent circuit models (ECMs) are presented to model the responses of the cell to linearly polarized waves at normal incidence. The ECMs show how utilizing interlayer coupling can be leveraged to achieve reversed CP senses in two bands using a compact design. Analytical formulas are presented to provide initial values of the ECM components including the mutual coupling inductances. We present measurement results that agree well with the full-wave simulation and the ECM results, thus validating the proposed ECM model.

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Research paper thumbnail of 3-D-Printed Transmit-Array Antenna for Broadband Backhaul 5G Links at V-Band

S. A. Matos et al., "3-D-Printed Transmit-Array Antenna for Broadband Backhaul 5G Links at V-Band," in IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 6, pp. 977-981, June 2020., Apr 6, 2020

The low cost and compactness of transmit-array antennas (TAs) make them attractive for 5G backhau... more The low cost and compactness of transmit-array antennas (TAs) make them attractive for 5G backhaul links. However, the TA advantage is less obvious when considering the broadband operation requirement. Two main factors influence the bandwidth performance, namely: 1) the bandwidth of the unit cells, and 2) the number of 360°phase wrapping zones in the aperture, which are designed for a specific frequency. Herein, we overcome these limitations by using all-dielectric unit cells (inherently broadband) and by developing a general method to quantify and manage the intricate relation between antenna gain, bandwidth, and antenna height. Based on this framework we optimize, as an example, a TA design (focal distance, F = 63 mm and aperture diameter D = 80 mm) to comply with typical gain specification for 5G backhaul links (>30 dBi) in the WiGiG band (from 57 to 66 GHz). The feed is a dedicated compact horn (8 × 5 × 22 mm 3) that provides a proper illumination of the aperture. Additive manufacturing is used to simplify the manufacturing process of the antenna. A very good agreement between simulations and experimental results is obtained, achieving good aperture efficiency for this type of antenna (42%), which rivals with existing solutions based on more expensive manufacturing techniques. Index Terms-5G backhaul link, additive manufacturing, transmit-array, V-band horn antenna, WiGiG band.

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Research paper thumbnail of Microwave Breast Imaging Using a Dry Setup

J. M. Felício et al., "Microwave Breast Imaging Using a Dry Setup", in IEEE Transactions on Computational Imaging, vol. 6, no. 12, pp. 167-180, 2020, Jan 2020

This article demonstrates for the first time, both numerically and experimentally, the feasibilit... more This article demonstrates for the first time, both numerically and experimentally, the feasibility of radar-based microwave imaging of anthropomorphic heterogeneously dense breasts in prone position, requiring no immersion liquid. The dry, contactless approach greatly simplifies the setup, favors patient comfort, and further avoids lengthy sanitation procedures after each exam. We use a radar-type technique with the antennas distributed in cylindrical configuration around the breast phantom. The reflectivity map is reconstructed using a wave-migration algorithm in the frequency domain. This article presents new developed strategies to cope with the challenges of a dry setup, namely increased skin artifact due to the concomitant absence of matching liquid and nonuniform breast shape. We propose an iterative and adaptive algorithm based on singular value decomposition that effectively removes the skin backscattering under the abovementioned conditions. It is compatible with automatic processing, and computationally fast. One of its inputs is the breast three-dimensional surface information, and its distance to the antennas, all obtained automatically from a proposed low-cost procedure based on a webcam. The imaging method is reasonably resilient to the presence of fibroglandular tissues, and to uncertainties of tissue permittivity. Another tackled challenge is the miniaturization of the antenna in air, which is achieved with an optimized balanced antipodal Vivaldi of the same size as counterparts used in dense immersion liquids. Finally, all the building blocks are combined to demonstrate experimentally the overall dry system performance, with very good detection of the tumor at three different positions in the breast, even in low-contrast scenarios. Index Terms-Artifact removal, balanced antipodal Vivaldi antenna (BAVA), breast surface estimation, broadband antenna, dry imaging setup, heterogeneous breast imaging, inverse problem , medical microwave imaging (MWI), phantom, singular value decomposition (SVD), skin backscattering, cascade transmission line, wave-migration.

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Research paper thumbnail of Efficient Evaluation of Gradient Transmit-Arrays Through an Equivalent Dispersive Dielectric Description

P. Naseri, S. A. Matos, E. B. Lima, J. R. Costa, C. A. Fernandes and N. J. G. Fonseca, "Efficient Evaluation of Gradient Transmit-Arrays Through an Equivalent Dispersive Dielectric Description," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 9, pp. 5997-6007, Sept. 2019., Sep 2019

The growing popularity of transmit-arrays (TAs) for various antenna applications is calling for e... more The growing popularity of transmit-arrays (TAs) for various antenna applications is calling for effective analysis and optimization methods. TAs are, usually, electrically large, comprising thousands of unit-cells formed by subwavelength metallic scatterers. Full-wave optimization cycles needed to meet stringent specifications in terms of gain, cross-polarization, band-width, scan-loss, etc., may be impaired by unrealistically required computational time and memory resources. To overcome this, we propose a modified homogenization method that, unlike other approaches, captures the internal reflections in the unit-cells and its resonances for each polarization, thus, correctly describing unit-cells' frequency response in the band of interest. We define equivalent dispersive anisotropic media for gradient TAs. These surrogate models enable fast analysis and optimization of TAs without compromising the accuracy. As an example, we analyze a TA composed of phase rotation (PR) unit-cells. PR unit-cells present wideband low axial ratio for a TA but challenge the validation of existing homogenization methods. Detailed general description of the method is provided so that it can be applied to other unit-cells and avoid training time and resources required for machine learning-based methods. Using the surrogate cells, the full-wave analysis time and memory of the TA reduces 13 and 4 times, respectively.

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Research paper thumbnail of Multiple-Beam Focal-Plane Dual-Band Fabry-Pérot Cavity Antenna With Reduced Beam Degradation

E. B. Lima, J. R. Costa and C. A. Fernandes, "Multiple-Beam Focal-Plane Dual-Band Fabry–Pérot Cavity Antenna With Reduced Beam Degradation," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 7, pp. 4348-4356, July 2019., 2019

Focal-plane reflector feeds with shared aperture are a promising solution for the increasing numb... more Focal-plane reflector feeds with shared aperture are a promising solution for the increasing number of beams required in the Ka-band satellite services. Stringent manufacturing tolerances and coupling between feeds tend to penalize performance, which is aggravated for a dual band. This paper proposes a new design of a shared aperture antenna intended for multispot single-feed-per beam satellite applications that allows recovering single-feed performance, minimizing the usual impact of adjacent feeds on the field distribution and ultimately on the antenna directivity and gain. We present a new focal-plane dual-band Fabry-Pérot cavity antenna (FPCA) design, which allows more reliable fabrication, closer agreement with simulations, and larger bandwidth than the reported solutions. It uses only one double-sided printed frequency-selective surface (FSS) to form the dual-band FPCA, and it is fed through a novel arrangement of double-layer slots in the FPCA-printed ground plane. This favors impedance matching and higher isolation between adjacent feeds. The effectiveness of the solution is experimentally demonstrated for a single-feed Ka-band (20 and 30 GHz) prototype. The generalization for a complete multifeed configuration with filters is shown by full-wave simulations. The decoupling slots on the FPCA ground plane enable restoring single-feed performance in the multifeed system, over the bandwidth of interest. Index Terms-Closed square loop (CSL), decoupling slots, dual band, Fabry-Pérot cavity antenna (FPCA), feed slots, focal-plane array (FPA), frequency-selective surface (FSS), Ka-band, multiple beams, reflection coefficient.

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Research paper thumbnail of Antenna Design and Near-Field Characterization for Medical Microwave Imaging Applications

J. M. Felício, J. M. Bioucas-Dias, J. R. Costa and C. A. Fernandes, "Antenna Design and Near-Field Characterization for Medical Microwave Imaging Applications," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 7, pp. 4811-4824, July 2019., 2019

In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body... more In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body and are required to pick up weak echoes from the inside that are masked by high skin reflection. The near-field antenna behavior strongly determines how the received signals affect the effectiveness of the imaging algorithms. However, these usually simply assume the usual antenna far-field radiation characteristics. Here, we discuss three antenna effects that can deteriorate the overall imaging performance but are rarely addressed in the literature: antenna internal reflections, angular dispersion of the "near-field phase center," and antenna frequency dispersive electric length. We propose dedicated methods to characterize these factors and present mitigation strategies to be integrated into the inversion algorithms. We demonstrate these effects for three frequently used broadband antennas, using signals from an experimental breast imaging lab setup. In fact, the antenna study and design cannot ignore that it operates in the near field of breast and interacts with its boundary. The methods and conclusions can be extended to other MMWI applications. To the best of our knowledge, this is the first systematic study of the above antenna factors in the context of MMWI. Index Terms-Antenna calibration, antenna design, balanced antipodal Vivaldi antenna (BAVA), breast imaging, microwave imaging (MWI), near-field imaging, planar monopole antenna, slot antenna, ultrawideband antenna.

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Research paper thumbnail of Dual-Band Dual-Linear-to-Circular Polarization Converter in Transmission Mode Application to K /Ka-Band Satellite Communications

P. Naseri, S. Matos, J. Costa, C. Fernandes and, N. Fonseca, "Dual-Band Dual Linear to Circular Polarization Converter in Transmission Mode-Application to K/Ka-Band Satellite Communications", in IEEE Transactions on Antennas and Propagation, vol. 66, no. 12, pp. 7128-7137, Dec. 2018, Dec 2018

Many wireless communication applications such as satellite communications use circularly polarize... more Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications , the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm × 5.3 mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer. Index Terms— Antenna–filter–antenna, circular polarization (CP), dual-band antennas, frequency selective surfaces, periodic structures, polarization conversion.

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Research paper thumbnail of Synthesis of Shaped-Beam Radiation Patterns at Millimeter-Waves Using Transmit Arrays

C. C. Cruz, C. A. Fernandes, S. A. Matos and J. R. Costa, "Synthesis of Shaped-Beam Radiation Patterns at Millimeter-Waves Using Transmit Arrays," in IEEE Transactions on Antennas and Propagation, vol. 66, no. 8, pp. 4017-4024, Aug. 2018., Aug 2018

Transmit arrays have been mostly used for beam collimation applications, either with fixed or sca... more Transmit arrays have been mostly used for beam collimation applications, either with fixed or scanning beam capability. But transmit arrays can also be used to synthesize power radiation patterns complying with power pattern templates. A new analytical formulation is presented here to obtain a phase-only correction function corresponding to a given power template. The transmit-array transforms the known power radiation pattern of the primary source into a desired output power pattern. The proposed formulation, specialized for axial-symmetric structures, is based on geometrical optics and provides the solution directly from the evaluation of two closed-form first-order differential equations. As a proof of concept, a sec 2 with a roll-off at 45° is defined as the target power pattern, at the 30 GHz Ka-band. A 10.8 dBi radiation pattern with the circular polarization is used to illuminate a 180 mm × 180 mm transmit array with 60 mm focal distance. Previously designed 3.35 mm thick phase-delay unit cells are used as an example to implement the calculated phase distribution over the transmit-array aperture. The measured antenna radiation pattern matches quite well the template, with a steep fall of the radiation at the roll-off angle and low cross-polarization. This validates the concept, the formulation, and the fabricated prototype. Index Terms— Geometrical optics (GO), millimeter-wave antennas, planar lens antennas, radiation pattern shaping, secant squared power pattern, transmit arrays.

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Research paper thumbnail of Dual-Band Skin-Adhesive Repeater Antenna for Continuous Body Signals Monitoring

J. M. Felício, J. R. Costa and C. A. Fernandes, "Dual-Band Skin-Adhesive Repeater Antenna for Continuous Body Signals Monitoring," in IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, vol. 2, no. 1, pp. 25-32, March 2018., Mar 2018

We present a 35-mm diameter skin-adhesive antenna intended to operate as a gateway to relay the l... more We present a 35-mm diameter skin-adhesive antenna intended to operate as a gateway to relay the low power signals from a sensor implanted in the body to an external base station (BS). Such a device would be useful in the context of body area networks (BANs) for continuous body-signal monitoring. The proposed adhesive repeater is of very low profile, and it is designed for dual-band operation at the ISM band (2.4 GHz) and in the ultrawideband (UWB) spectrum (4–10.6 GHz) using a single exci-tation port. The ISM band is used for in-body communication with the implants and the UWB band for off-body burst communication with the BS. The antenna consists of three layers that grant it compactness and performance robustness. We assess the in-body link between the repeater and a custom-designed miniaturized im-plantable probe antenna. The study is performed in the frequency domain with results showing adequate input impedance matching (s 11 −10 dB) and robustness to different body parts. We extend the analysis to time domain by transmitting a synthetized medical signal between the two antennas. In addition, we evaluate the feasibility of an off-body link for burst communication. Again, the results indicate very good performance by the repeater antenna both in terms of impedance matching (s 11 −10 dB) and preservation of time signals (fidelity 75%), which is relevant in impulse radio systems. To the authors' best knowledge, this is the first time this kind of dual-band adhesive antenna is being proposed for BANs, complete with performance tests using frequency-and time-domain figures-of-merit. Index Terms—Body area network, body-centric communication, implantable antenna, in-body communication, off-body communication , on-body antenna, quadrature-phase shift keying (QPSK), time-domain measurement, ultrawideband antenna.

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Research paper thumbnail of Phase-Delay Versus Phase-Rotation Cells for Circular Polarization Transmit Arrays—Application to Satellite Ka-Band Beam Steering

P. Naseri, S. A. Matos, J. R. Costa and C. A. Fernandes, "Phase-Delay Versus Phase-Rotation Cells for Circular Polarization Transmit Arrays—Application to Satellite Ka-Band Beam Steering," in IEEE Transactions on Antennas and Propagation, vol. 66, no. 3, pp. 1236-1247, March 2018., 2018

Planar transmit arrays (TAs) have been an attractive solution as gain enhancers for various appli... more Planar transmit arrays (TAs) have been an attractive solution as gain enhancers for various applications, e.g., satellite communications. The TA performance directly depends on its composing unit-cell characteristics. Planar unit cells can be categorized into two main types: phase-rotation (PR) and phase-delay (PD) cells. There is no hint in the literature about the relative merits of these two types of cells for circular polarization when assessing the final TA performance. This paper offers a systematic comparison between the cells' working principles and analyzes their impacts on TA performance. Examples of a PR-based TA and a PD-based TA are designed for single-band wide-angle beam steering operating at the satellite Ka-band. They are evaluated by simulation and measurement to quantify performance differences. No previous work employed a PR TA for wide-angle beam steering. This paper shows that PR TA offers a filtering effect toward the cross-polarization component of the source. This leads to better axial ratio and combined 3 dB axial ratio and 3 dB gain bandwidth. However, PD cells are easier to design and insensitive to feed polarization. The analysis in this paper allows a more informed decision when selecting the unit-cell category for any given TA application. Index Terms— Circular polarization (CP), flat lens, frequency-selective surface (FSS), mechanical scanning, satellite on the move (SOTM), transmit arrays (TAs), wireless communication network.

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Research paper thumbnail of Three-dimensional printed ABS plastic peanut-lens with integrated ball grid array module for high-data-rate communications in F-band

A. Bisognin et al., "Three-dimensional printed ABS plastic peanut-lens with integrated ball grid array module for high-data-rate communications in F-band", IET Microwaves, Antennas & Propagation, vol. 11, no. 14, pp. 2021-2026, 2017, Nov 19, 2017

A ball grid array (BGA) module integrated within a three-dimensional printed peanut-shaped lens i... more A ball grid array (BGA) module integrated within a three-dimensional printed peanut-shaped lens is proposed for high-data-rate wireless communications in the F-band (116–140 GHz) between a video camera and a TV or a laptop. The module implements a 1 × 2 array antenna which radiates a wide beam in the horizontal plane (H-plane) and a narrower beam in the vertical plane (E-plane). The dielectric lens, fabricated in ABS-M30 plastic, is a shaped lens designed to achieve a fan-beam radiation pattern further narrowing the vertical plane and widening the horizontal plane of the BGA module. The realised gain of the full antenna system is required to exceed 5 dBi within a 120° angular interval in the horizontal plane and a 20° angular interval in the vertical plane. Measurements show a reflection coefficient below −9 dB from 116 to 140 GHz and a maximum realised gain of 8.5 dBi at 130 GHz demonstrating feasibility of the cost-effective proposed design for a high-data-rate communications.

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Research paper thumbnail of Experimental verification of 'waveguide' plasmonics

Surface plasmons polaritons are collective excitations of an electron gas that occur at an interf... more Surface plasmons polaritons are collective excitations of an electron gas that occur at an interface between negative-ε and positive-ε media. Here, we report the experimental observation of such surface waves using simple waveguide metamaterials filled only with available positive-ε media at microwave frequencies. In contrast to optical designs, in our setup the propagation length of the surface plasmons can be rather long as low loss conventional dielectrics are chosen to avoid typical losses from negative-ε media. Plasmonic phenomena have potential applications in enhancing light– matter interactions, implementing nanoscale photonic circuits and integrated photonics.

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Research paper thumbnail of Ball Grid Array Module With Integrated Shaped Lens for 5G Backhaul/Fronthaul Communications in F-Band

In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic l... more In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic lens antenna for application in a dedicated 130 GHz OOK transceiver that targets the area of 5G backhaul/fronthaul systems. The main design goal was the full integration of a small footprint antenna with an energy-efficient transceiver. The antenna system must be compact and cost effective while delivering an approximately 30 dBi gain in the working band, defined as 120 to 140 GHz. Accordingly, a 2 × 2 array of aperture-coupled patch antennas was designed in the 7 × 7 × 0.362 mm 3 BGA module as the feed antenna of the lens. This achieved a 7.8 dBi realized gain, broadside polarization purity above 20 dB, and over 55% total efficiency from 110 to 140 GHz (20% bandwidth). A plastic elliptical lens 40 mm in diameter and 42.3 mm in height was placed on top of the BGA module. The antenna achieved a return loss better than −10 dB and a 28 dBi realized gain from 114 to 140 GHz. Finally, active measurements demonstrated a >12 Gbps Tx/Rx link at 5 m with bit error rate (BER) < 10 −6 at 1.6 pJ/b/m. These results pave the way for future cost-effective, energy-efficient, high-data rate backhaul/fronthaul systems for 5G communications. Index Terms— 3-D printing, 5G, backhaul/fronthaul links, ball grid array (BGA), dielectric lens, millimeter-wave (mmw) antennas, organic module.

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Research paper thumbnail of High Gain Dual-Band Beam-Steering Transmit Array for Satcom Terminals at Ka-Band

Transmit array design is more challenging for dual-band operation than for single band, due to th... more Transmit array design is more challenging for dual-band operation than for single band, due to the independent 360° phase wrapping jumps needed at each band when large electrical length compensation is involved. This happens when aiming at large gains, typically above 25 dBi with beam scanning and F/ D ≤ 1. No such designs have been reported in the literature. A general method is presented here to reduce the complexity of dual-band transmit array design, valid for arbitrarily large phase error compensation and any band ratio, using a finite number of different unit cells. The procedure is demonstrated for two offset transmit array implementations operating in circular polarization at 20 GHz(Rx) and 30 GHz(Tx) for Ka-band satellite-on-the-move terminals with mechanical beam-steering. An appropriate set of 30 dual-band unit cells is developed with transmission coefficient greater than −0.9 dB. The full-size transmit array is characterized by full-wave simulation enabling elevation beam scanning over 0°−50° with gains reaching 26 dBi at 20 GHz and 29 dBi at 30 GHz. A smaller prototype was fabricated and measured, showing a measured gain of 24 dBi at 20 GHz and 27 dBi at 30 GHz. In both cases, the beam pointing direction is coincident over the two frequency bands, and thus confirming the proposed design procedure.

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Research paper thumbnail of Wideband and High-Selectivity Dual-Band Filter for Ka-Band Satellite Antennas

A dual-band miniaturized Ka-band filter is presented, taking advantage of transmission in cutoff ... more A dual-band miniaturized Ka-band filter is presented, taking advantage of transmission in cutoff rectangular waveguides periodically loaded in the E-plane with split-ring resonators (SRRs). High selectivity, wide bandwidth, and high out-of-band rejection are achieved in a compact form factor. The use of SRRs in a waveguide configuration proves to be a valid and promising solution for the design of dual-band filters. The filter is specifically designed for Ka-band, and a prototype was manufactured and its performance measured, providing a reasonably flat transmission at both 20-and 30-GHz subbands. For both bands, the power roll-off rate is higher than 55 dB/decade, translating into a sharper than 10-dB drop per 0.2 GHz in a 38 × 6.6 × 4.5-mm 3 device. The filter half-power bandwidth is B_20 = 1.1 GHz at 20 GHz (18.4–19.5 GHz) and B_30 = 1.2 GHz at 30 GHz (27.8–29.0 GHz).

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Research paper thumbnail of Stereolithography-Based Antennas for Satellite Communications in Ka-Band

This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize ... more This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize high-performance low-cost antennas for Ka-band applications. In addition to the inherent electromagnetic challenges implicit in the conception of such complex devices, this paper also points out the stringent limitations that appear when opting for classical fabrication techniques, based on assembled split-block models. AM emerges in this context as a change of paradigm, allowing mono-lithic fabrication and design freedom, which result in substantial improvements in terms of compactness, mass, simplicity, cost, and production time. Two different antennas for Ka-band satellite communications are presented here, namely a wideband horn and a dual-band circular cavity. Both prototypes are fabricated using a stereolithographic (SLA) AM process followed by metal coating. This fabrication approach is especially well suited to the implementation of these designs, since they have internal shapes that are inaccessible to conventional machining tools. The experimental results are not only in very good agreement with the theoretical predictions but also demonstrate improvements over the performances achieved by traditional milling and assembly fabrication approaches, thereby confirming the validity and great potential of SLA for Ka-band satellite communications.

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Research paper thumbnail of Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band

Vaquero, Á.F.; Pino, M.R.; Arrebola, M.; Matos, S.A.; Costa, J.R.; Fernandes, C.A. Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band. Sensors 2021, 21, 422., Jan 2001

A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region... more A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region of the antenna in the Ka-band. The antenna is designed to focus the radiated field at a certain point using a central feeding configuration. The number of feeds is increased to create as many focusing spots as feeds. The feeds are placed along an arc defined in the principal planes of the transmitarray, radiating independent near-field spots and providing a solution with a wide-angle spot scanning without an antenna displacement and a high isolation between feeds. To validate this concept, a transmitarray based on dielectric-only cells is designed and simulated under full-wave conditions. Then, this design is manufactured using a 3D printing technique, and the prototype is measured in a planar acquisition range. Measurements are performed for different feed positions in order to validate the multi-focusing capability of the antenna. Measurements and simulations show a high agreement and validate the proposed design technique.

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Research paper thumbnail of Bessel Beam Generation Using Dielectric Planar Lenses at Millimeter Frequencies

Á. F. Vaquero, M. R. Pino, M. Arrebola, S. A. Matos, J. R. Costa and C. A. Fernandes, "Bessel Beam Generation Using Dielectric Planar Lenses at Millimeter Frequencies," in IEEE Access, vol. 8, pp. 216185-216196, 2020, Dec 2020

In this work a dielectric planar lens is proposed to generate a Bessel beam. The lens works at Ka... more In this work a dielectric planar lens is proposed to generate a Bessel beam. The lens works at Ka-band and produces a non-diffraction range within the Fresnel region of the antenna. The methodology to design the aperture antenna at millimetre or microwave frequencies is presented. It is applied to a dielectric planar lens made up of cells that shapes the radiated near-field by adjusting the unit cell response. An approach based on a second order polynomial is proposed to consider the angular dependence of the phase-shift response of the cell in the designing process. In order to implement the lens physically, two novel cells, based on rectangular and hexagonal prisms, are proposed, and their performance is compared. The cells ensure the index dielectric media variation using airgaps to control the overall density of the material. After fully characterizing the cells, a design is carried out for the two proposed type of cells. The requirement for the Bessel beam is a depth-of-field of 650 mm at 28 GHz. After evaluating the design in a full-wave simulation, both prototypes were manufactured using a 3-D printing technique. Finally, the prototypes were measured in a planar acquisition range to evaluate the performances of the Bessel beam. Both lenses show a good agreement between simulations and measurements, obtaining promising results in the Bessel beam generation by index-graded dielectric lenses at Ka-band. INDEX TERMS Dielectric lenses, Bessel beams, near-field focusing.

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Research paper thumbnail of Applying Massively Parallel Computing to Multiscale Ka Dual-Band Transmit-Array Analysis Using FETI-2LM

A. Barka, S. A. Matos, J. R. Costa, C. A. Fernandes and H. Chreim, "Applying Massively Parallel Computing to Multiscale Ka Dual-Band Transmit-Array Analysis Using FETI-2LM," in IEEE Journal on Multiscale and Multiphysics Computational Techniques, vol. 5, pp. 235-244, 2020, Nov 2020

Transmit-arrays (TAs) are a popular cost-effective solution for high-gain antennas at millimeter ... more Transmit-arrays (TAs) are a popular cost-effective solution for high-gain antennas at millimeter waves. The design of these antennas relies on the fine tuning of the subwavelength unit cells that compose the aperture. The intricacy of the unit cells increases as new features are implemented, such as dual-band operation and wide-angle beam steering, making this antenna even more computationally challenging. In this article, a high-gain (25 dBi @ 20 GHz and 28 dBi @ 30 GHz) multiscale Ka dual-band TA for beam-steering applications is analyzed using a massively parallel implementation on multicores clusters of the finite element tearing and interconnecting method, with a two Lagrange multiplier (FETI-2LM) technique. The main contribution of this article is the implementation of 3-D nonperiodic grids with subdomains of different scales, that is suitable for proper modeling of different regions of the antenna (horn feed, lens cells, and air region). An automatic batch file procedure is proposed for the TA meshing, allowing the limited set of constitutive unit cells of the TA to be meshed separately. Additionally, we are using a block-Krylov strategy to efficiently capture the TA beam-steering capability, without restarting from scratch the interface problem for each feed position. Since other finite element method results were not accessible due the size of the problem, the FETI-2LM numerical results provided in this article are compared with other multilevel fast multipole methods and transmission line modeling method of CST Microwave Studio solvers, as well as with the measured results of the corresponding Ka dual-band prototype. The computational infrastructure has been used only a fraction of its capacity. Therefore , a much higher gain design (40 dBi) can be assessed, opening a new realm of applicability of TAs in the space segment usually occupied by reflector-based solutions. Fig. 1. TA beam-steering antenna concept implemented in [2] for dual-band operation. Focal distance between the horn and the lens F = 100 mm, length along the X-axis D ax = 196 mm, and width along the Y-axis D ay = 147 mm. Index Terms-Domain decomposition, finite element method (FEM), finite element tearing and interconnecting (FETI), GID preprocessor, Ka-band transmit-array (TA), Krylov spaces.

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Research paper thumbnail of Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment

Savazzi, M.; Abedi, S.; Ištuk, N.; Joachimowicz, N.; Roussel, H.; Porter, E.; O’Halloran, M.; Costa, J.R.; Fernandes, C.A.; Felício, J.M.; Conceição, R.C. Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment. Sensors 2020, 20, 4968., 2020

We produced an anatomically and dielectrically realistic phantom of the axillary region to enable... more We produced an anatomically and dielectrically realistic phantom of the axillary region to enable the experimental assessment of Axillary Lymph Node (ALN) imaging using microwave imaging technology. We segmented a thoracic Computed Tomography (CT) scan and created a computer-aided designed file containing the anatomical configuration of the axillary region. The phantom comprises five 3D-printed parts representing the main tissues of interest of the axillary region for the purpose of microwave imaging: fat, muscle, bone, ALNs, and lung. The phantom allows the experimental assessment of multiple anatomical configurations, by including ALNs of different size, shape, and number in several locations. Except for the bone mimicking organ, which is made of solid conductive polymer, we 3D-printed cavities to represent the fat, muscle, ALN, and lung and filled them with appropriate tissue-mimicking liquids. Existing studies about complex permittivity of ALNs have reported limitations. To address these, we measured the complex permittivity of both human and animal lymph nodes using the standard open-ended coaxial-probe technique, over the 0.5 GHz-8.5 GHz frequency band, thus extending current knowledge on dielectric properties of ALNs. Lastly, we numerically evaluated the effect of the polymer which constitutes the cavities of the phantom and compared it to the realistic axillary region. The results showed a maximum difference of 7 dB at 4 GHz in the electric field magnitude coupled to the tissues and a maximum of 10 dB difference in the ALN response. Our results showed that the phantom is a good representation of the axillary region and a viable tool for pre-clinical assessment of microwave imaging technology.

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Research paper thumbnail of Communication Equivalent Circuit Modeling to Design a Dual-Band Dual Linear-to-Circular Polarizer Surface

P. Naseri, J. R. Costa, S. A. Matos, C. A. Fernandes and S. V. Hum, "Equivalent Circuit Modeling to Design a Dual-Band Dual Linear-to-Circular Polarizer Surface," in IEEE Transactions on Antennas and Propagation, vol. 68, no. 7, pp. 5730-5735, July 2020., 2020

The working principle of a thin dual-band dual-linear to circular polarizer is presented here. Th... more The working principle of a thin dual-band dual-linear to circular polarizer is presented here. This polarizer not only converts incident linearly polarized (LP) waves to circularly polarized (CP) waves in two frequency bands, but it also reverses the handedness of each signal. The electromagnetic behavior of the cell is carefully analyzed and two equivalent circuit models (ECMs) are presented to model the responses of the cell to linearly polarized waves at normal incidence. The ECMs show how utilizing interlayer coupling can be leveraged to achieve reversed CP senses in two bands using a compact design. Analytical formulas are presented to provide initial values of the ECM components including the mutual coupling inductances. We present measurement results that agree well with the full-wave simulation and the ECM results, thus validating the proposed ECM model.

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Research paper thumbnail of 3-D-Printed Transmit-Array Antenna for Broadband Backhaul 5G Links at V-Band

S. A. Matos et al., "3-D-Printed Transmit-Array Antenna for Broadband Backhaul 5G Links at V-Band," in IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 6, pp. 977-981, June 2020., Apr 6, 2020

The low cost and compactness of transmit-array antennas (TAs) make them attractive for 5G backhau... more The low cost and compactness of transmit-array antennas (TAs) make them attractive for 5G backhaul links. However, the TA advantage is less obvious when considering the broadband operation requirement. Two main factors influence the bandwidth performance, namely: 1) the bandwidth of the unit cells, and 2) the number of 360°phase wrapping zones in the aperture, which are designed for a specific frequency. Herein, we overcome these limitations by using all-dielectric unit cells (inherently broadband) and by developing a general method to quantify and manage the intricate relation between antenna gain, bandwidth, and antenna height. Based on this framework we optimize, as an example, a TA design (focal distance, F = 63 mm and aperture diameter D = 80 mm) to comply with typical gain specification for 5G backhaul links (>30 dBi) in the WiGiG band (from 57 to 66 GHz). The feed is a dedicated compact horn (8 × 5 × 22 mm 3) that provides a proper illumination of the aperture. Additive manufacturing is used to simplify the manufacturing process of the antenna. A very good agreement between simulations and experimental results is obtained, achieving good aperture efficiency for this type of antenna (42%), which rivals with existing solutions based on more expensive manufacturing techniques. Index Terms-5G backhaul link, additive manufacturing, transmit-array, V-band horn antenna, WiGiG band.

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Research paper thumbnail of Microwave Breast Imaging Using a Dry Setup

J. M. Felício et al., "Microwave Breast Imaging Using a Dry Setup", in IEEE Transactions on Computational Imaging, vol. 6, no. 12, pp. 167-180, 2020, Jan 2020

This article demonstrates for the first time, both numerically and experimentally, the feasibilit... more This article demonstrates for the first time, both numerically and experimentally, the feasibility of radar-based microwave imaging of anthropomorphic heterogeneously dense breasts in prone position, requiring no immersion liquid. The dry, contactless approach greatly simplifies the setup, favors patient comfort, and further avoids lengthy sanitation procedures after each exam. We use a radar-type technique with the antennas distributed in cylindrical configuration around the breast phantom. The reflectivity map is reconstructed using a wave-migration algorithm in the frequency domain. This article presents new developed strategies to cope with the challenges of a dry setup, namely increased skin artifact due to the concomitant absence of matching liquid and nonuniform breast shape. We propose an iterative and adaptive algorithm based on singular value decomposition that effectively removes the skin backscattering under the abovementioned conditions. It is compatible with automatic processing, and computationally fast. One of its inputs is the breast three-dimensional surface information, and its distance to the antennas, all obtained automatically from a proposed low-cost procedure based on a webcam. The imaging method is reasonably resilient to the presence of fibroglandular tissues, and to uncertainties of tissue permittivity. Another tackled challenge is the miniaturization of the antenna in air, which is achieved with an optimized balanced antipodal Vivaldi of the same size as counterparts used in dense immersion liquids. Finally, all the building blocks are combined to demonstrate experimentally the overall dry system performance, with very good detection of the tumor at three different positions in the breast, even in low-contrast scenarios. Index Terms-Artifact removal, balanced antipodal Vivaldi antenna (BAVA), breast surface estimation, broadband antenna, dry imaging setup, heterogeneous breast imaging, inverse problem , medical microwave imaging (MWI), phantom, singular value decomposition (SVD), skin backscattering, cascade transmission line, wave-migration.

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Research paper thumbnail of Efficient Evaluation of Gradient Transmit-Arrays Through an Equivalent Dispersive Dielectric Description

P. Naseri, S. A. Matos, E. B. Lima, J. R. Costa, C. A. Fernandes and N. J. G. Fonseca, "Efficient Evaluation of Gradient Transmit-Arrays Through an Equivalent Dispersive Dielectric Description," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 9, pp. 5997-6007, Sept. 2019., Sep 2019

The growing popularity of transmit-arrays (TAs) for various antenna applications is calling for e... more The growing popularity of transmit-arrays (TAs) for various antenna applications is calling for effective analysis and optimization methods. TAs are, usually, electrically large, comprising thousands of unit-cells formed by subwavelength metallic scatterers. Full-wave optimization cycles needed to meet stringent specifications in terms of gain, cross-polarization, band-width, scan-loss, etc., may be impaired by unrealistically required computational time and memory resources. To overcome this, we propose a modified homogenization method that, unlike other approaches, captures the internal reflections in the unit-cells and its resonances for each polarization, thus, correctly describing unit-cells' frequency response in the band of interest. We define equivalent dispersive anisotropic media for gradient TAs. These surrogate models enable fast analysis and optimization of TAs without compromising the accuracy. As an example, we analyze a TA composed of phase rotation (PR) unit-cells. PR unit-cells present wideband low axial ratio for a TA but challenge the validation of existing homogenization methods. Detailed general description of the method is provided so that it can be applied to other unit-cells and avoid training time and resources required for machine learning-based methods. Using the surrogate cells, the full-wave analysis time and memory of the TA reduces 13 and 4 times, respectively.

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Research paper thumbnail of Multiple-Beam Focal-Plane Dual-Band Fabry-Pérot Cavity Antenna With Reduced Beam Degradation

E. B. Lima, J. R. Costa and C. A. Fernandes, "Multiple-Beam Focal-Plane Dual-Band Fabry–Pérot Cavity Antenna With Reduced Beam Degradation," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 7, pp. 4348-4356, July 2019., 2019

Focal-plane reflector feeds with shared aperture are a promising solution for the increasing numb... more Focal-plane reflector feeds with shared aperture are a promising solution for the increasing number of beams required in the Ka-band satellite services. Stringent manufacturing tolerances and coupling between feeds tend to penalize performance, which is aggravated for a dual band. This paper proposes a new design of a shared aperture antenna intended for multispot single-feed-per beam satellite applications that allows recovering single-feed performance, minimizing the usual impact of adjacent feeds on the field distribution and ultimately on the antenna directivity and gain. We present a new focal-plane dual-band Fabry-Pérot cavity antenna (FPCA) design, which allows more reliable fabrication, closer agreement with simulations, and larger bandwidth than the reported solutions. It uses only one double-sided printed frequency-selective surface (FSS) to form the dual-band FPCA, and it is fed through a novel arrangement of double-layer slots in the FPCA-printed ground plane. This favors impedance matching and higher isolation between adjacent feeds. The effectiveness of the solution is experimentally demonstrated for a single-feed Ka-band (20 and 30 GHz) prototype. The generalization for a complete multifeed configuration with filters is shown by full-wave simulations. The decoupling slots on the FPCA ground plane enable restoring single-feed performance in the multifeed system, over the bandwidth of interest. Index Terms-Closed square loop (CSL), decoupling slots, dual band, Fabry-Pérot cavity antenna (FPCA), feed slots, focal-plane array (FPA), frequency-selective surface (FSS), Ka-band, multiple beams, reflection coefficient.

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Research paper thumbnail of Antenna Design and Near-Field Characterization for Medical Microwave Imaging Applications

J. M. Felício, J. M. Bioucas-Dias, J. R. Costa and C. A. Fernandes, "Antenna Design and Near-Field Characterization for Medical Microwave Imaging Applications," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 7, pp. 4811-4824, July 2019., 2019

In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body... more In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body and are required to pick up weak echoes from the inside that are masked by high skin reflection. The near-field antenna behavior strongly determines how the received signals affect the effectiveness of the imaging algorithms. However, these usually simply assume the usual antenna far-field radiation characteristics. Here, we discuss three antenna effects that can deteriorate the overall imaging performance but are rarely addressed in the literature: antenna internal reflections, angular dispersion of the "near-field phase center," and antenna frequency dispersive electric length. We propose dedicated methods to characterize these factors and present mitigation strategies to be integrated into the inversion algorithms. We demonstrate these effects for three frequently used broadband antennas, using signals from an experimental breast imaging lab setup. In fact, the antenna study and design cannot ignore that it operates in the near field of breast and interacts with its boundary. The methods and conclusions can be extended to other MMWI applications. To the best of our knowledge, this is the first systematic study of the above antenna factors in the context of MMWI. Index Terms-Antenna calibration, antenna design, balanced antipodal Vivaldi antenna (BAVA), breast imaging, microwave imaging (MWI), near-field imaging, planar monopole antenna, slot antenna, ultrawideband antenna.

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Research paper thumbnail of Dual-Band Dual-Linear-to-Circular Polarization Converter in Transmission Mode Application to K /Ka-Band Satellite Communications

P. Naseri, S. Matos, J. Costa, C. Fernandes and, N. Fonseca, "Dual-Band Dual Linear to Circular Polarization Converter in Transmission Mode-Application to K/Ka-Band Satellite Communications", in IEEE Transactions on Antennas and Propagation, vol. 66, no. 12, pp. 7128-7137, Dec. 2018, Dec 2018

Many wireless communication applications such as satellite communications use circularly polarize... more Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications , the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm × 5.3 mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer. Index Terms— Antenna–filter–antenna, circular polarization (CP), dual-band antennas, frequency selective surfaces, periodic structures, polarization conversion.

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Research paper thumbnail of Synthesis of Shaped-Beam Radiation Patterns at Millimeter-Waves Using Transmit Arrays

C. C. Cruz, C. A. Fernandes, S. A. Matos and J. R. Costa, "Synthesis of Shaped-Beam Radiation Patterns at Millimeter-Waves Using Transmit Arrays," in IEEE Transactions on Antennas and Propagation, vol. 66, no. 8, pp. 4017-4024, Aug. 2018., Aug 2018

Transmit arrays have been mostly used for beam collimation applications, either with fixed or sca... more Transmit arrays have been mostly used for beam collimation applications, either with fixed or scanning beam capability. But transmit arrays can also be used to synthesize power radiation patterns complying with power pattern templates. A new analytical formulation is presented here to obtain a phase-only correction function corresponding to a given power template. The transmit-array transforms the known power radiation pattern of the primary source into a desired output power pattern. The proposed formulation, specialized for axial-symmetric structures, is based on geometrical optics and provides the solution directly from the evaluation of two closed-form first-order differential equations. As a proof of concept, a sec 2 with a roll-off at 45° is defined as the target power pattern, at the 30 GHz Ka-band. A 10.8 dBi radiation pattern with the circular polarization is used to illuminate a 180 mm × 180 mm transmit array with 60 mm focal distance. Previously designed 3.35 mm thick phase-delay unit cells are used as an example to implement the calculated phase distribution over the transmit-array aperture. The measured antenna radiation pattern matches quite well the template, with a steep fall of the radiation at the roll-off angle and low cross-polarization. This validates the concept, the formulation, and the fabricated prototype. Index Terms— Geometrical optics (GO), millimeter-wave antennas, planar lens antennas, radiation pattern shaping, secant squared power pattern, transmit arrays.

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Research paper thumbnail of Dual-Band Skin-Adhesive Repeater Antenna for Continuous Body Signals Monitoring

J. M. Felício, J. R. Costa and C. A. Fernandes, "Dual-Band Skin-Adhesive Repeater Antenna for Continuous Body Signals Monitoring," in IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, vol. 2, no. 1, pp. 25-32, March 2018., Mar 2018

We present a 35-mm diameter skin-adhesive antenna intended to operate as a gateway to relay the l... more We present a 35-mm diameter skin-adhesive antenna intended to operate as a gateway to relay the low power signals from a sensor implanted in the body to an external base station (BS). Such a device would be useful in the context of body area networks (BANs) for continuous body-signal monitoring. The proposed adhesive repeater is of very low profile, and it is designed for dual-band operation at the ISM band (2.4 GHz) and in the ultrawideband (UWB) spectrum (4–10.6 GHz) using a single exci-tation port. The ISM band is used for in-body communication with the implants and the UWB band for off-body burst communication with the BS. The antenna consists of three layers that grant it compactness and performance robustness. We assess the in-body link between the repeater and a custom-designed miniaturized im-plantable probe antenna. The study is performed in the frequency domain with results showing adequate input impedance matching (s 11 −10 dB) and robustness to different body parts. We extend the analysis to time domain by transmitting a synthetized medical signal between the two antennas. In addition, we evaluate the feasibility of an off-body link for burst communication. Again, the results indicate very good performance by the repeater antenna both in terms of impedance matching (s 11 −10 dB) and preservation of time signals (fidelity 75%), which is relevant in impulse radio systems. To the authors' best knowledge, this is the first time this kind of dual-band adhesive antenna is being proposed for BANs, complete with performance tests using frequency-and time-domain figures-of-merit. Index Terms—Body area network, body-centric communication, implantable antenna, in-body communication, off-body communication , on-body antenna, quadrature-phase shift keying (QPSK), time-domain measurement, ultrawideband antenna.

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Research paper thumbnail of Phase-Delay Versus Phase-Rotation Cells for Circular Polarization Transmit Arrays—Application to Satellite Ka-Band Beam Steering

P. Naseri, S. A. Matos, J. R. Costa and C. A. Fernandes, "Phase-Delay Versus Phase-Rotation Cells for Circular Polarization Transmit Arrays—Application to Satellite Ka-Band Beam Steering," in IEEE Transactions on Antennas and Propagation, vol. 66, no. 3, pp. 1236-1247, March 2018., 2018

Planar transmit arrays (TAs) have been an attractive solution as gain enhancers for various appli... more Planar transmit arrays (TAs) have been an attractive solution as gain enhancers for various applications, e.g., satellite communications. The TA performance directly depends on its composing unit-cell characteristics. Planar unit cells can be categorized into two main types: phase-rotation (PR) and phase-delay (PD) cells. There is no hint in the literature about the relative merits of these two types of cells for circular polarization when assessing the final TA performance. This paper offers a systematic comparison between the cells' working principles and analyzes their impacts on TA performance. Examples of a PR-based TA and a PD-based TA are designed for single-band wide-angle beam steering operating at the satellite Ka-band. They are evaluated by simulation and measurement to quantify performance differences. No previous work employed a PR TA for wide-angle beam steering. This paper shows that PR TA offers a filtering effect toward the cross-polarization component of the source. This leads to better axial ratio and combined 3 dB axial ratio and 3 dB gain bandwidth. However, PD cells are easier to design and insensitive to feed polarization. The analysis in this paper allows a more informed decision when selecting the unit-cell category for any given TA application. Index Terms— Circular polarization (CP), flat lens, frequency-selective surface (FSS), mechanical scanning, satellite on the move (SOTM), transmit arrays (TAs), wireless communication network.

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Research paper thumbnail of Three-dimensional printed ABS plastic peanut-lens with integrated ball grid array module for high-data-rate communications in F-band

A. Bisognin et al., "Three-dimensional printed ABS plastic peanut-lens with integrated ball grid array module for high-data-rate communications in F-band", IET Microwaves, Antennas & Propagation, vol. 11, no. 14, pp. 2021-2026, 2017, Nov 19, 2017

A ball grid array (BGA) module integrated within a three-dimensional printed peanut-shaped lens i... more A ball grid array (BGA) module integrated within a three-dimensional printed peanut-shaped lens is proposed for high-data-rate wireless communications in the F-band (116–140 GHz) between a video camera and a TV or a laptop. The module implements a 1 × 2 array antenna which radiates a wide beam in the horizontal plane (H-plane) and a narrower beam in the vertical plane (E-plane). The dielectric lens, fabricated in ABS-M30 plastic, is a shaped lens designed to achieve a fan-beam radiation pattern further narrowing the vertical plane and widening the horizontal plane of the BGA module. The realised gain of the full antenna system is required to exceed 5 dBi within a 120° angular interval in the horizontal plane and a 20° angular interval in the vertical plane. Measurements show a reflection coefficient below −9 dB from 116 to 140 GHz and a maximum realised gain of 8.5 dBi at 130 GHz demonstrating feasibility of the cost-effective proposed design for a high-data-rate communications.

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Research paper thumbnail of Experimental verification of 'waveguide' plasmonics

Surface plasmons polaritons are collective excitations of an electron gas that occur at an interf... more Surface plasmons polaritons are collective excitations of an electron gas that occur at an interface between negative-ε and positive-ε media. Here, we report the experimental observation of such surface waves using simple waveguide metamaterials filled only with available positive-ε media at microwave frequencies. In contrast to optical designs, in our setup the propagation length of the surface plasmons can be rather long as low loss conventional dielectrics are chosen to avoid typical losses from negative-ε media. Plasmonic phenomena have potential applications in enhancing light– matter interactions, implementing nanoscale photonic circuits and integrated photonics.

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Research paper thumbnail of Ball Grid Array Module With Integrated Shaped Lens for 5G Backhaul/Fronthaul Communications in F-Band

In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic l... more In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic lens antenna for application in a dedicated 130 GHz OOK transceiver that targets the area of 5G backhaul/fronthaul systems. The main design goal was the full integration of a small footprint antenna with an energy-efficient transceiver. The antenna system must be compact and cost effective while delivering an approximately 30 dBi gain in the working band, defined as 120 to 140 GHz. Accordingly, a 2 × 2 array of aperture-coupled patch antennas was designed in the 7 × 7 × 0.362 mm 3 BGA module as the feed antenna of the lens. This achieved a 7.8 dBi realized gain, broadside polarization purity above 20 dB, and over 55% total efficiency from 110 to 140 GHz (20% bandwidth). A plastic elliptical lens 40 mm in diameter and 42.3 mm in height was placed on top of the BGA module. The antenna achieved a return loss better than −10 dB and a 28 dBi realized gain from 114 to 140 GHz. Finally, active measurements demonstrated a >12 Gbps Tx/Rx link at 5 m with bit error rate (BER) < 10 −6 at 1.6 pJ/b/m. These results pave the way for future cost-effective, energy-efficient, high-data rate backhaul/fronthaul systems for 5G communications. Index Terms— 3-D printing, 5G, backhaul/fronthaul links, ball grid array (BGA), dielectric lens, millimeter-wave (mmw) antennas, organic module.

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Research paper thumbnail of High Gain Dual-Band Beam-Steering Transmit Array for Satcom Terminals at Ka-Band

Transmit array design is more challenging for dual-band operation than for single band, due to th... more Transmit array design is more challenging for dual-band operation than for single band, due to the independent 360° phase wrapping jumps needed at each band when large electrical length compensation is involved. This happens when aiming at large gains, typically above 25 dBi with beam scanning and F/ D ≤ 1. No such designs have been reported in the literature. A general method is presented here to reduce the complexity of dual-band transmit array design, valid for arbitrarily large phase error compensation and any band ratio, using a finite number of different unit cells. The procedure is demonstrated for two offset transmit array implementations operating in circular polarization at 20 GHz(Rx) and 30 GHz(Tx) for Ka-band satellite-on-the-move terminals with mechanical beam-steering. An appropriate set of 30 dual-band unit cells is developed with transmission coefficient greater than −0.9 dB. The full-size transmit array is characterized by full-wave simulation enabling elevation beam scanning over 0°−50° with gains reaching 26 dBi at 20 GHz and 29 dBi at 30 GHz. A smaller prototype was fabricated and measured, showing a measured gain of 24 dBi at 20 GHz and 27 dBi at 30 GHz. In both cases, the beam pointing direction is coincident over the two frequency bands, and thus confirming the proposed design procedure.

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Research paper thumbnail of Wideband and High-Selectivity Dual-Band Filter for Ka-Band Satellite Antennas

A dual-band miniaturized Ka-band filter is presented, taking advantage of transmission in cutoff ... more A dual-band miniaturized Ka-band filter is presented, taking advantage of transmission in cutoff rectangular waveguides periodically loaded in the E-plane with split-ring resonators (SRRs). High selectivity, wide bandwidth, and high out-of-band rejection are achieved in a compact form factor. The use of SRRs in a waveguide configuration proves to be a valid and promising solution for the design of dual-band filters. The filter is specifically designed for Ka-band, and a prototype was manufactured and its performance measured, providing a reasonably flat transmission at both 20-and 30-GHz subbands. For both bands, the power roll-off rate is higher than 55 dB/decade, translating into a sharper than 10-dB drop per 0.2 GHz in a 38 × 6.6 × 4.5-mm 3 device. The filter half-power bandwidth is B_20 = 1.1 GHz at 20 GHz (18.4–19.5 GHz) and B_30 = 1.2 GHz at 30 GHz (27.8–29.0 GHz).

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Research paper thumbnail of Stereolithography-Based Antennas for Satellite Communications in Ka-Band

This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize ... more This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize high-performance low-cost antennas for Ka-band applications. In addition to the inherent electromagnetic challenges implicit in the conception of such complex devices, this paper also points out the stringent limitations that appear when opting for classical fabrication techniques, based on assembled split-block models. AM emerges in this context as a change of paradigm, allowing mono-lithic fabrication and design freedom, which result in substantial improvements in terms of compactness, mass, simplicity, cost, and production time. Two different antennas for Ka-band satellite communications are presented here, namely a wideband horn and a dual-band circular cavity. Both prototypes are fabricated using a stereolithographic (SLA) AM process followed by metal coating. This fabrication approach is especially well suited to the implementation of these designs, since they have internal shapes that are inaccessible to conventional machining tools. The experimental results are not only in very good agreement with the theoretical predictions but also demonstrate improvements over the performances achieved by traditional milling and assembly fabrication approaches, thereby confirming the validity and great potential of SLA for Ka-band satellite communications.

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Research paper thumbnail of Double-shell modified extended hemispherical lens feed for reflectors in scanning applications

European Conference on Antennas and Propagation, Apr 11, 2011

A new dielectric lens antenna configuration is described, intended to feed a quasi-optical imagin... more A new dielectric lens antenna configuration is described, intended to feed a quasi-optical imaging reflector system. The lens is fed at its base by a 5 pixel array, each one producing an output beam after the reflector with near 61 dBi directivity. The lens is designed in such a way that it produces virtual foci outside the lens body, close to the reflector focal arch. The lens plus reflector system provides a maximum scanning angle of α = ±0.36º in elevation with gain scan loss below 1.1dB, while a mechanical rotation of the reflector produces azimuth scan.

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Research paper thumbnail of Amplification of Wavelength Division Multiplexing in Multi-Core Erbium Doped Fiber Amplifiers

Abstract This paper presents a study of multi-core erbium doped couplers as an alternative to con... more Abstract This paper presents a study of multi-core erbium doped couplers as an alternative to conventional erbium-doped fiber amplifiers. The couplers can reduce the power unbalance between WDM channels along an optical communication link. Different configurations of couplers are analyzed and the influence of the number of cores is studied.

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Research paper thumbnail of Permittivity measurement and anisotropy evaluation of dielectric materials at millimeter-waves

Abstract− This paper describes the design and use of an open Fabry-Perot resonator to evaluate th... more Abstract− This paper describes the design and use of an open Fabry-Perot resonator to evaluate the degree of anisotropy of dielectric material samples at millimeterwaves. The proposed implementation not only allows identifying the orientation of the dielectric principal axes but also determining the complex permittivity values along these axes. Keywords Dielectric permittivity measurements, Anisotropy, Fabry-Perot resonator.

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Research paper thumbnail of Integrated imaging lens antenna with broadband feeds

Abstract The paper explores the use of a recently introduced printed broadband antenna based on c... more Abstract The paper explores the use of a recently introduced printed broadband antenna based on crossed exponential slot configuration for multiple-feed excitation of an integrated lens antenna. The new patch is compact, it presents very good linear polarisation and it is especially adequate for integrated lens antenna feeding at millimetre waves and sub-millimetre waves, even allowing for convenient integration of a mixer at the back-face of the antenna substrate.

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Research paper thumbnail of Double-shell axial-symmetric imaging lens antenna for space applications

Abstract This paper describes the design of a double-material imaging lens that focuses incoming ... more Abstract This paper describes the design of a double-material imaging lens that focuses incoming off-axis beams into narrowband sensors distributed at the lens base. A shaped double-shell approach is adopted as a strategy for increasing design degrees of freedom as opposed to the classical single-material extended hemispherical lens configuration.

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Research paper thumbnail of Calculation of the near-field from axial symmetric apertures using Gaussian-like discretization of the aperture field

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Research paper thumbnail of An array of crossed metallic wires as a metamaterial with extreme index of refraction

Abstract In a recent work [Phys. Rev. B, 78, 033108, 2008] we have suggested that an array of cro... more Abstract In a recent work [Phys. Rev. B, 78, 033108, 2008] we have suggested that an array of crossed metallic wires may interact with an electromagnetic wave as a material with an extreme index of refraction. Here, we will present our ongoing work on such metamaterials, and discuss the physics of the extreme index of refraction property and possible applications.

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Research paper thumbnail of Pulse Switching in Nonlinear Fiber Bragg Gratings

Abstract The influence of the Kerr-like nonlinearity in the switching characteristics of fiber Br... more Abstract The influence of the Kerr-like nonlinearity in the switching characteristics of fiber Bragg gratings is studied. Two types of apodization profiles are considered: uniform and raisedcosine apodized gratings. The influence of the bit-rate and the wavelength detuning of the incident pulses in the nonlinear response of the grating is analyzed. The deterioration in the pulses caused by the nonlinear effects is also observed.

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Research paper thumbnail of A numerical study of WDM pulse equalization in twin-core fiber amplifiers

Abstract We present a numerical study of twin-core fiber amplifiers to be used in WDM soliton com... more Abstract We present a numerical study of twin-core fiber amplifiers to be used in WDM soliton communication systems. The equalization capability and the influence on the shape of soliton-like pulses are both investigated. Different pulse widths, corresponding to different bit-rate systems, are also considered

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Research paper thumbnail of Integrated Lens Antennas

Aperture Antennas for Millimeter and Sub-Millimeter Wave Applications, 2017

This chapter presents the Integrated Lens Antenna (ILA) technology as it evolved since its introd... more This chapter presents the Integrated Lens Antenna (ILA) technology as it evolved since its introduction aiming to respond to the needs of emerging applications such as high-data-rate communication, intelligent transport, and mm-wave imaging. The topics covered include the ILA design concepts as well as the electromagnetic phenomena intrinsic to dielectric lenses that may affect ILA performance. The aspects of the ILA technology related to selection of the primary feeds, lens materials, and fabrication methods are also revised. A few practical examples are provided to illustrate the current and future trends of this technology.

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Research paper thumbnail of Dielectric Lens Antennas

Handbook of Antenna Technologies, 2016

Dielectric lens antennas are attracting a renewed interest for millimetre-and sub-millimetre wave... more Dielectric lens antennas are attracting a renewed interest for millimetre-and sub-millimetre wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications. This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discuss ion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas.

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