George Kyriacou | Democritus University of Thrace (original) (raw)

Papers by George Kyriacou

Multiple feeding technique is herein used to provide wideband operation for a super-shaped patch ... more Multiple feeding technique is herein used to provide wideband operation for a super-shaped patch radiator. Four symmetrical feeding points are exploited to create an overlapping loss pattern, yielding a functional bandwidth of 2 GHz. The initial hypothesis is evaluated in terms of all appropriate antenna characteristics such as Return Loss, VSWR, input impedance, efficiency and corresponding radiation patterns.

IEEE Transactions on Antennas and Propagation, Dec 1, 2022

The goal of this paper is to investigate the performance of MIMO-WCDMA networks, where Principal ... more The goal of this paper is to investigate the performance of MIMO-WCDMA networks, where Principal Component Analysis (PCA) is employed at the reception. Multipath propagation is exploited, as the individual received signals can be seen as different instances of the same physical phenomenon (i.e. transmission and reception of WCDMA sequences). In this context, the received data are first transformed using an orthogonal representation. Afterwards, the constructed covariance matrix is used in order to reduce the overall complexity of a proposed transmission strategy for signal transmission in MIMO-WCDMA networks in diversity combining transmission mode. As results indicate, for a 2×2 MIMO orientation (i.e. two transmit and receive antennas) and six multipath components, the complexity of the proposed algorithm can be reduced up to 15%/60% for SNR equal to 0/5 dB, respectively.

In the present work, a new technique for ultra-wideband radio frequency beamform- ing, based on t... more In the present work, a new technique for ultra-wideband radio frequency beamform- ing, based on the microwave photonics techniques, is introduced. It makes use of high frequency microwave networks to process low radio frequency (RF) wideband signals. The general concept is elaborated, along with its applications to ultra-wideband RF phased arrays. Both transmit and receive modules are designed, concentrating on the beamforming networks, which are based on the well known Butler matrix. Simulation results are presented in detail, whereas comparisons and remarks on future work are given in the end. 1. INTRODUCTION Radio frequency systems have been used in a large variety of applications, such as communications, military, aviation and atmospheric (ionospheric) research. Throughout the years, the need for wideband operation has become more intense, since systems' requirements demand broadband operation in multiple octaves. Many radio frequency systems use phased arrays (or multibeam antennas) for transmit/receive operation, exploiting beamforming and directional beam-steering. This necessity became inevitable with the current trend towards Software Deflned Radio (SDR) and Cognitive Radio (CR). Their concepts ask for digitally (software) controllable and multifunctional radio frequency front-ends. Regarding the antenna this demand is translated to ultra-wideband structures able to precisely control their beam direction and radiation pattern shaping, but should be miniaturized to yield compact structures conformably integrated over the device package (e.g., mobile unit). Thus, a wideband phased array must be integrated in the system. However, nontrivial di-culties arise when trying to design a wideband array, since the operation frequency band of the components is always limited. Despite that, quite enough wideband systems have been operated, presenting an operational frequency range of a few octaves. In this study, a new technique for ultra-wideband radio frequency beamforming is presented. The technique mimics the principles of \microwave photonics" systems, where a microwave signal is translated into the optical regime, using an electro-optical modulator and an optical signal as a carrier (1,2). The modulated signal is processed with optical circuitry. The use of the optical carrier signal allows for the processing of ultra-wideband microwave signals, which occupy a very small fraction (percent) of bandwidth at the high optical frequencies, thus operational bandwidth extends up to many GHz. That means that an ultra-wideband microwave signal can be operated and processed, without the need for wideband techniques. As far as microwave phased arrays are concerned, the microwave signal modulates an optical carrier which is in turn split into a number of channels equal to the number of the antenna elements. The modulated optical signal in each channel undergoes the desired phase shift, which is the same independently of the microwave frequency (within a multiple GHz band), thus introducing the desired true-time delay (TTD). The signal of each channel is then demodulated by a simple diode detector, amplifled accordingly and fed to the corresponding antenna element. A similar approach is followed in the receiver. This technique is called photonic beamforming (2,3). The same design principle is used herein, to accomplish ultra-wideband operation for radio frequency signals. The carrier signal used now is a microwave one, which exhibits an operational bandwidth of about 5{10%, that is, a few hundreds of MHz. This operational bandwidth constitutes a multiple octave bandwidth for a radio frequency signal with a frequency of several MHz. Thus, the microwave carrier signal ofiers ultra-wideband operation to the radio frequency signal.

Iet Microwaves Antennas & Propagation, Dec 4, 2021

Progress in Electromagnetics Research B, 2020

This work aims at completing the Wiener-Hopf analysis of a canonical problem referring to an extr... more This work aims at completing the Wiener-Hopf analysis of a canonical problem referring to an extraordinary transverse electromagnetic wave propagating within a parallel plane waveguide loaded with magnetized plasma when incident normally at the truncated edge of its upper conductor. The complicated mathematical issues faced herein comes from the non-symmetric Kernel functions involved in the related integral equation. This property puts two challenging issues, first the rarely occurring factorization of non-symmetric Kernels and secondly the handling of unidirectional surface and leaky waves. Although the formulation of the Wiener-Hopf equations was carried out in our previous work, these two challenges were not confronted, since that work has been completed only in regard to the closed-shielded geometry which involves a symmetric Kernel. Thus, the novel contribution of this work refers to completing the analysis of the open geometry by handling the factorization of the related non-symmetric Kernel, evaluating the radiated field as well as studying the unidirectional waves for their near and far fields.

A slotted antenna array consisting of two rectangular cavities is introduced. The primary resonat... more A slotted antenna array consisting of two rectangular cavities is introduced. The primary resonating cavity is probe fed, while the second one is fed through a 45° obverted slot placed on the segregating surface between them. This technique results in enhanced bandwidth operation without the need for designing a special feeding network. The array operates throughout a bandwidth of 257.4 MHz centered around the frequency of 2.5 GHz, and presents omnidirectional patterns in the E and H-plane, making up a good choice for multipath environments.

Progress in Electromagnetics Research Symposium, 2015

This work elaborates on the design of an Ultra-Wideband (UWB) Butler matrix fed antenna array, im... more This work elaborates on the design of an Ultra-Wideband (UWB) Butler matrix fed antenna array, implementing a Multiple Input-Multiple Output (MIMO) configuration. The system aims at applications in ...

A novel quadruple feeding mechanism for a rectangular patch antenna is proposed. A successive pha... more A novel quadruple feeding mechanism for a rectangular patch antenna is proposed. A successive phase shift caused by path inequality between four possible symmetrical feeding points is introduced, in order to achieve wideband operation at the 2 GHz frequency band. This work is an extension to the idea of acquiring a pair of resonances and forcing them to behave in a consolidated way. This concept is verified in previous work and is herein stretched to the limit that a rectangular patch could provide speaking in terms of symmetry, i.e. using four feeding points. The proposed antenna exhibits a fractional bandwidth of 3.46 %, almost four times as much as the conventional single-fed patch does. Furthermore, the antenna presents circular polarization and an elevationuniform radiation pattern. VSWR, Impedance matching as well as Antenna and Radiation Efficiency are also presented and annotated.

A novel feeding mechanism for a rectangular patch antenna is introduced. A phase shift caused by ... more A novel feeding mechanism for a rectangular patch antenna is introduced. A phase shift caused by path inequality between two possible symmetrical feeding points is introduced, in order to achieve wideband operation at the 2.4 GHz WiFi band. The idea is to create two separate resonances, by exploiting a phase shift in one of the feeds. Simultaneously activating the two feeds yields to an envelope formed by the separate resonances. This leads to a fractional bandwidth enhancement from 0.9% to about 1.8%. The feeding mechanism is furthermore folded on the back side of the patch, thus constructing an appropriate design for cellular applications, reducing its size. This configuration leads to an even better fractional bandwidth enhancement (53.07 MHz, i.e. 2.18%). The results are verified in terms of Return Loss, Input Impedance, VSWR and Antenna and Radiation Efficiency, all exhibiting satisfactory behaviour.

2022 IEEE International Symposium on Phased Array Systems & Technology (PAST), Oct 11, 2022

Modern simulation applications that carry out large scale iterative processes, such as Monte-Carl... more Modern simulation applications that carry out large scale iterative processes, such as Monte-Carlo simulations, or manipulate large data structures, tend to be extremely timeconsuming due to the shortage of computational resources or the inherent nature of the simulation itself. Typical simulations can take up to several days to complete on conventional systems, while high-end supercomputers can be cost-prohibitive. Therefore, the need for effective parallelization of software execution and resource management is more imperative. The goal of this paper is to present a fully-distributed platform that enables software simulations to be executed within user-acceptable time periods, by predicting the resource requirements of each simulation. In this context, the platform analyzes files that contain historical data about past executions of the particular simulation. Processor and memory utilization, overall execution time, level of parallelization and distributed execution are some of the information collected and used by an efficient training algorithm, in order to determine the optimal amount of resources to be allocated in a particular simulation. The training algorithm applies several machine-learning techniques such as multi-linear regression in order to efficiently predict the resource vector that will satisfy the user requirements.

European Conference on Antennas and Propagation, May 13, 2015

A patch antenna with two rectangular elements is presented. The feeding mechanism introduces a ph... more A patch antenna with two rectangular elements is presented. The feeding mechanism introduces a phase shift between the elements excitation, as well as between the feeding points of each element. The Return Loss versus Frequency envelope which is then formed extends greatly as each feeding point contributes to the creation of a separate resonance. In this way, wideband operation at the 2.4 GHz WiFi band is achieved. Specifically, this new configuration exhibits a bandwidth of 84.69 MHz which is a fair improvement concerning the size - bandwidth tradeoff. The results are verified in terms of Return Loss, VSWR, Input Impedance, Antenna and Radiation Efficiency, all demonstrating compensatory behaviour.

Computing of wave propagation and radiation through periodic band gap structures and their unique... more Computing of wave propagation and radiation through periodic band gap structures and their unique electromagnetic features attracted a huge research interest during the last decades. These features enabled the development of novel metamaterials and were exploited in frequency selective surfaces, phased arrays and numerous electromagnetic bandgap applications. Moreover, the metamaterials including photonic crystals are extensively investigated in the fields of optics, microwave, and antenna engineering due to their inherent possibility to develop novel devices that may not be found until now, [Huan Xie and Ya Yan Lu, J. Opt. Soc. Am. A 26, 2009, pp. 1606-1614]. Thus, the analysis and design of such structures have received particular attention which is almost exclusively directed toward the deterministic numerical simulations. Even though this analysis served as a very useful tool, it does not offer the required physical insight, while it does not provide any means to devise novel structures.

The technique of multiple points feeding in order to achieve improved bandwidth performance is he... more The technique of multiple points feeding in order to achieve improved bandwidth performance is here exploited and used to feed a supershape structured radiator. The achieved operating bandwidth, is an important advancement compared to the performance of the usual, single fed and regularly shaped patch antennas. The proposed antenna operates from 2.5 to 3.9 GHz with linear polarization and its behavior is investigated in terms of Return Loss, VSWR, input impedance, radiation pattern, electric field and efficiency.

Multiple feeding technique is herein used to provide wideband operation for a super-shaped patch ... more Multiple feeding technique is herein used to provide wideband operation for a super-shaped patch radiator. Four symmetrical feeding points are exploited to create an overlapping loss pattern, yielding a functional bandwidth of 2 GHz. The initial hypothesis is evaluated in terms of all appropriate antenna characteristics such as Return Loss, VSWR, input impedance, efficiency and corresponding radiation patterns.

IEEE Transactions on Antennas and Propagation, Dec 1, 2022

The goal of this paper is to investigate the performance of MIMO-WCDMA networks, where Principal ... more The goal of this paper is to investigate the performance of MIMO-WCDMA networks, where Principal Component Analysis (PCA) is employed at the reception. Multipath propagation is exploited, as the individual received signals can be seen as different instances of the same physical phenomenon (i.e. transmission and reception of WCDMA sequences). In this context, the received data are first transformed using an orthogonal representation. Afterwards, the constructed covariance matrix is used in order to reduce the overall complexity of a proposed transmission strategy for signal transmission in MIMO-WCDMA networks in diversity combining transmission mode. As results indicate, for a 2×2 MIMO orientation (i.e. two transmit and receive antennas) and six multipath components, the complexity of the proposed algorithm can be reduced up to 15%/60% for SNR equal to 0/5 dB, respectively.

In the present work, a new technique for ultra-wideband radio frequency beamform- ing, based on t... more In the present work, a new technique for ultra-wideband radio frequency beamform- ing, based on the microwave photonics techniques, is introduced. It makes use of high frequency microwave networks to process low radio frequency (RF) wideband signals. The general concept is elaborated, along with its applications to ultra-wideband RF phased arrays. Both transmit and receive modules are designed, concentrating on the beamforming networks, which are based on the well known Butler matrix. Simulation results are presented in detail, whereas comparisons and remarks on future work are given in the end. 1. INTRODUCTION Radio frequency systems have been used in a large variety of applications, such as communications, military, aviation and atmospheric (ionospheric) research. Throughout the years, the need for wideband operation has become more intense, since systems' requirements demand broadband operation in multiple octaves. Many radio frequency systems use phased arrays (or multibeam antennas) for transmit/receive operation, exploiting beamforming and directional beam-steering. This necessity became inevitable with the current trend towards Software Deflned Radio (SDR) and Cognitive Radio (CR). Their concepts ask for digitally (software) controllable and multifunctional radio frequency front-ends. Regarding the antenna this demand is translated to ultra-wideband structures able to precisely control their beam direction and radiation pattern shaping, but should be miniaturized to yield compact structures conformably integrated over the device package (e.g., mobile unit). Thus, a wideband phased array must be integrated in the system. However, nontrivial di-culties arise when trying to design a wideband array, since the operation frequency band of the components is always limited. Despite that, quite enough wideband systems have been operated, presenting an operational frequency range of a few octaves. In this study, a new technique for ultra-wideband radio frequency beamforming is presented. The technique mimics the principles of \microwave photonics" systems, where a microwave signal is translated into the optical regime, using an electro-optical modulator and an optical signal as a carrier (1,2). The modulated signal is processed with optical circuitry. The use of the optical carrier signal allows for the processing of ultra-wideband microwave signals, which occupy a very small fraction (percent) of bandwidth at the high optical frequencies, thus operational bandwidth extends up to many GHz. That means that an ultra-wideband microwave signal can be operated and processed, without the need for wideband techniques. As far as microwave phased arrays are concerned, the microwave signal modulates an optical carrier which is in turn split into a number of channels equal to the number of the antenna elements. The modulated optical signal in each channel undergoes the desired phase shift, which is the same independently of the microwave frequency (within a multiple GHz band), thus introducing the desired true-time delay (TTD). The signal of each channel is then demodulated by a simple diode detector, amplifled accordingly and fed to the corresponding antenna element. A similar approach is followed in the receiver. This technique is called photonic beamforming (2,3). The same design principle is used herein, to accomplish ultra-wideband operation for radio frequency signals. The carrier signal used now is a microwave one, which exhibits an operational bandwidth of about 5{10%, that is, a few hundreds of MHz. This operational bandwidth constitutes a multiple octave bandwidth for a radio frequency signal with a frequency of several MHz. Thus, the microwave carrier signal ofiers ultra-wideband operation to the radio frequency signal.

Iet Microwaves Antennas & Propagation, Dec 4, 2021

Progress in Electromagnetics Research B, 2020

This work aims at completing the Wiener-Hopf analysis of a canonical problem referring to an extr... more This work aims at completing the Wiener-Hopf analysis of a canonical problem referring to an extraordinary transverse electromagnetic wave propagating within a parallel plane waveguide loaded with magnetized plasma when incident normally at the truncated edge of its upper conductor. The complicated mathematical issues faced herein comes from the non-symmetric Kernel functions involved in the related integral equation. This property puts two challenging issues, first the rarely occurring factorization of non-symmetric Kernels and secondly the handling of unidirectional surface and leaky waves. Although the formulation of the Wiener-Hopf equations was carried out in our previous work, these two challenges were not confronted, since that work has been completed only in regard to the closed-shielded geometry which involves a symmetric Kernel. Thus, the novel contribution of this work refers to completing the analysis of the open geometry by handling the factorization of the related non-symmetric Kernel, evaluating the radiated field as well as studying the unidirectional waves for their near and far fields.

A slotted antenna array consisting of two rectangular cavities is introduced. The primary resonat... more A slotted antenna array consisting of two rectangular cavities is introduced. The primary resonating cavity is probe fed, while the second one is fed through a 45° obverted slot placed on the segregating surface between them. This technique results in enhanced bandwidth operation without the need for designing a special feeding network. The array operates throughout a bandwidth of 257.4 MHz centered around the frequency of 2.5 GHz, and presents omnidirectional patterns in the E and H-plane, making up a good choice for multipath environments.

Progress in Electromagnetics Research Symposium, 2015

This work elaborates on the design of an Ultra-Wideband (UWB) Butler matrix fed antenna array, im... more This work elaborates on the design of an Ultra-Wideband (UWB) Butler matrix fed antenna array, implementing a Multiple Input-Multiple Output (MIMO) configuration. The system aims at applications in ...

A novel quadruple feeding mechanism for a rectangular patch antenna is proposed. A successive pha... more A novel quadruple feeding mechanism for a rectangular patch antenna is proposed. A successive phase shift caused by path inequality between four possible symmetrical feeding points is introduced, in order to achieve wideband operation at the 2 GHz frequency band. This work is an extension to the idea of acquiring a pair of resonances and forcing them to behave in a consolidated way. This concept is verified in previous work and is herein stretched to the limit that a rectangular patch could provide speaking in terms of symmetry, i.e. using four feeding points. The proposed antenna exhibits a fractional bandwidth of 3.46 %, almost four times as much as the conventional single-fed patch does. Furthermore, the antenna presents circular polarization and an elevationuniform radiation pattern. VSWR, Impedance matching as well as Antenna and Radiation Efficiency are also presented and annotated.

A novel feeding mechanism for a rectangular patch antenna is introduced. A phase shift caused by ... more A novel feeding mechanism for a rectangular patch antenna is introduced. A phase shift caused by path inequality between two possible symmetrical feeding points is introduced, in order to achieve wideband operation at the 2.4 GHz WiFi band. The idea is to create two separate resonances, by exploiting a phase shift in one of the feeds. Simultaneously activating the two feeds yields to an envelope formed by the separate resonances. This leads to a fractional bandwidth enhancement from 0.9% to about 1.8%. The feeding mechanism is furthermore folded on the back side of the patch, thus constructing an appropriate design for cellular applications, reducing its size. This configuration leads to an even better fractional bandwidth enhancement (53.07 MHz, i.e. 2.18%). The results are verified in terms of Return Loss, Input Impedance, VSWR and Antenna and Radiation Efficiency, all exhibiting satisfactory behaviour.

2022 IEEE International Symposium on Phased Array Systems & Technology (PAST), Oct 11, 2022

Modern simulation applications that carry out large scale iterative processes, such as Monte-Carl... more Modern simulation applications that carry out large scale iterative processes, such as Monte-Carlo simulations, or manipulate large data structures, tend to be extremely timeconsuming due to the shortage of computational resources or the inherent nature of the simulation itself. Typical simulations can take up to several days to complete on conventional systems, while high-end supercomputers can be cost-prohibitive. Therefore, the need for effective parallelization of software execution and resource management is more imperative. The goal of this paper is to present a fully-distributed platform that enables software simulations to be executed within user-acceptable time periods, by predicting the resource requirements of each simulation. In this context, the platform analyzes files that contain historical data about past executions of the particular simulation. Processor and memory utilization, overall execution time, level of parallelization and distributed execution are some of the information collected and used by an efficient training algorithm, in order to determine the optimal amount of resources to be allocated in a particular simulation. The training algorithm applies several machine-learning techniques such as multi-linear regression in order to efficiently predict the resource vector that will satisfy the user requirements.

European Conference on Antennas and Propagation, May 13, 2015

A patch antenna with two rectangular elements is presented. The feeding mechanism introduces a ph... more A patch antenna with two rectangular elements is presented. The feeding mechanism introduces a phase shift between the elements excitation, as well as between the feeding points of each element. The Return Loss versus Frequency envelope which is then formed extends greatly as each feeding point contributes to the creation of a separate resonance. In this way, wideband operation at the 2.4 GHz WiFi band is achieved. Specifically, this new configuration exhibits a bandwidth of 84.69 MHz which is a fair improvement concerning the size - bandwidth tradeoff. The results are verified in terms of Return Loss, VSWR, Input Impedance, Antenna and Radiation Efficiency, all demonstrating compensatory behaviour.

Computing of wave propagation and radiation through periodic band gap structures and their unique... more Computing of wave propagation and radiation through periodic band gap structures and their unique electromagnetic features attracted a huge research interest during the last decades. These features enabled the development of novel metamaterials and were exploited in frequency selective surfaces, phased arrays and numerous electromagnetic bandgap applications. Moreover, the metamaterials including photonic crystals are extensively investigated in the fields of optics, microwave, and antenna engineering due to their inherent possibility to develop novel devices that may not be found until now, [Huan Xie and Ya Yan Lu, J. Opt. Soc. Am. A 26, 2009, pp. 1606-1614]. Thus, the analysis and design of such structures have received particular attention which is almost exclusively directed toward the deterministic numerical simulations. Even though this analysis served as a very useful tool, it does not offer the required physical insight, while it does not provide any means to devise novel structures.

The technique of multiple points feeding in order to achieve improved bandwidth performance is he... more The technique of multiple points feeding in order to achieve improved bandwidth performance is here exploited and used to feed a supershape structured radiator. The achieved operating bandwidth, is an important advancement compared to the performance of the usual, single fed and regularly shaped patch antennas. The proposed antenna operates from 2.5 to 3.9 GHz with linear polarization and its behavior is investigated in terms of Return Loss, VSWR, input impedance, radiation pattern, electric field and efficiency.