Jefferson Costa e Silva - Academia.edu (original) (raw)

Papers by Jefferson Costa e Silva

Micromachines, Mar 29, 2024

IEEE access, 2024

In this paper, a compact matryoshka DGS using dielectric resonator (DR) is proposed. Despite the ... more In this paper, a compact matryoshka DGS using dielectric resonator (DR) is proposed. Despite the use of dielectric resonators to obtain band-stop frequency response not being a new idea, the proposed compact matryoshka DGS is an original contribution, since only recently the matryoshka geometry was used in DGS applications. Furthermore, a numerical analysis of the positioning of the DR is presented, which makes it possible to determine the region of the DGS for which the minimum resonant frequency is reached, and the resonant frequency range that can be obtained. To the best of the authors' knowledge, this numerical analysis is an unpublished result, even more so, for the matryoshka DGS. The matryoshka geometry was described, including initial design equations. To verify the expected characteristics (miniaturization, selectivity, and resonant frequency tunability), two compact matryoshka DGSs (DGS1 and DGS2) were designed using a high permittivity ceramic (MCT-115) as DR. The obtained numerical and experimental results showed good agreement, and the initial design equations proved to be applicable, which allows new dimensions to be determined for other resonant frequencies, according to the application requirements. Resonant frequencies ranging from the maximum value to 33% (DGS1) and 27% (DGS2) were achieved, depending on the DR position. Considering 0 the wavelength in free space, corresponding to the resonant frequency, DGS1 and DGS2 achieved an occupied area of 0.04 0 × 0.04 0 , and 0.05 0 × 0.05 0 , respectively, a good miniaturization. The proposed compact matryoshka DGS may be especially attractive for applications that require a very selective band-stop frequency response. If a wider band-stop is required, the proposed DGS can be cascaded. INDEX TERMS Defected ground structure, DGS, dielectric resonator, high permittivity ceramic, matryoshka.

Revista Principia, Apr 7, 2023

Journal of Microwaves, Optoelectronics and Electromagnetic Applications, Mar 1, 2023

This work presents the development of a reconfigurable frequency selective surface (RFSS) for app... more This work presents the development of a reconfigurable frequency selective surface (RFSS) for application in the 2400-2483.5 MHz band, standard IEEE 802.11b/g/n (Wi-Fi). The proposed RFSS is based on the four-arms star geometry and PIN diodes were used as switching elements. In the initial design, numerical and measured results, especially for y polarization, PIN diode on-state, shown a difference of 15% for the resonant frequency. To overcome this drawback, a scaling factor was adopted and RFSS was redesigned and characterized, achieving the desired frequency response. The RFSS reconfigurability is confirmed, with a variation of at least 15 dB, when switching the states of the PIN diode. Moreover, the signal strength was measured directly on a notebook, confirming the reconfiguration of the RFSS. Finally, for the � polarization, it was found that for this polarization the frequency response remains virtually unchanged, even for angles of incidence up to 45°. In addition to the Wi-Fi signal control, the observed features make the developed RFSS especially attractive for reconfigurable antennas applications.

Microwave and Optical Technology Letters, Mar 21, 2016

Editora Conhecimento Livre eBooks, 2021

Federal do Rio Grande do Norte, como parte dos requisitos necessários para a obtenção do título d... more Federal do Rio Grande do Norte, como parte dos requisitos necessários para a obtenção do título de Doutor em Engenharia Elétrica.

In this work, we present a multiband FSS with open matryoshka elements obtained by the insertion ... more In this work, we present a multiband FSS with open matryoshka elements obtained by the insertion of a gap in the matryoshka ring. Taking into account the unit cell dimensions, very low resonant frequencies, up to Wx / λ 0 ≈. 0.065, and multiband behavior are observed, which are regarded as considerable advantages. The influence of the polarization is investigated and an approximate expression for the first resonance of the open matryoshka FSS is proposed. The frequency response for double rings, matryoshka and open matryoshka FSS are discussed. Three FSS, 2, 3 and 4 rings, were designed and fabricated using a low cost fiberglass substrate FR-4. The FSS were numerically and experimentally characterized, from 1.0 GHz to 18.0 GHz, considering both polarizations, x and y. Experimental results, when compared to numerical ones, present a very good agreement. Potential applications and the shown characteristics instigate other research groups to investigate the open matryoshka geometry.

This paper presents a parametric analysis of the use of angular inset-feed in different types of ... more This paper presents a parametric analysis of the use of angular inset-feed in different types of circular microstrip patch antennas, and its influence on the impedance matching of these structures. The proposed angular inset technique consists in make an opening in the conventional inset feed in order to improve the return loss (|S11| Parameter) and the impedance matching consequently. Also a modified expression is proposed for calculating the antenna input resistance having as reference the expression used for a conventional inset feed. It was simulated and measured antennas operating at frequencies of 1.4 GHz, 2.4 GHz and 5.0 GHz with good results. With the application of the proposed technique it was possible to obtain an improvement in the impedance matching of up to 33%. Numerical and experimental results are presented, being observed a good agreement between them.

DOAJ (DOAJ: Directory of Open Access Journals), Aug 1, 2015

F r a n c i s c o Od é c i o S a l e s (Or g a n i z a d o r) An o 2 0 2 1

Journal of Communication and Information Systems, 2020

This paper presents the development of a frequency selective surface, FSS, with three bands of re... more This paper presents the development of a frequency selective surface, FSS, with three bands of rejection, with the central bandwidth applied to the 2.4 GHz frequency band. Despite the fact that the main applications are in the 2.4 GHz frequency band, as emphasized in this paper, to reduce costs with scale production, it is interesting to note when the same FSS can be used for different applications such as wireless and cellular communications (1.71 GHz-1.93 GHz) and radio frequency localization (3.1 GHz-3.3GHz). The three rejection bands are obtained from the association of crossed-dipoles and matryoshka ring geometries. For each geometry the initial design equations are proposed. The procedure to obtain the matryoshka geometry is described step by step. Numerical results are presented for each geometry, and also to the associated geometries, considering different incident angles (θ=0°, 15°, 30° and 45°). The current distribution of each resonant frequency was shown, making it possible to visualize the respective excited geometry. After the numerical results, we verified that the resonant frequencies associated to the respective geometry remained practically unchanged even for the associated geometries. A FSS prototype with the associated geometries was designed, fabricated, and characterized, with a very good agreement between numerical and experimental results, obtaining an attenuation of at least 15 dB in the 2.4 GHz frequency band.

Iet Microwaves Antennas & Propagation, Apr 9, 2018

Reconfigurable frequency-selective surfaces (RFSSs) are of significant interest in applications, ... more Reconfigurable frequency-selective surfaces (RFSSs) are of significant interest in applications, such as secure communication systems or tunable radomes, to improve indoor communication and smart antennas. In order to change the frequency-selective surface (FSS) characteristics, and therefore its frequency response, conventional methods include loading with active semiconductor devices such as varactors, PIN diodes, Schottky diodes and radio-frequency microelectromechanical system. Another possibility is the use of mechanical adjusts, such as spring resonators or mechanical rotation. When PIN diodes are used, commonly only the reverse and forward regions, OFF and ON states, respectively, are considered. In this study, the implementation of an RFSS is described, using PIN diodes as active components. The RFSS is based on the fourarms star geometry, and initial design equations and procedures are presented. Numerical and measured results are shown for different project stages, with a very good agreement. In addition to obtaining two distinct resonant frequencies, due to the OFF and ON states, a third situation is included, considering the PIN diode threshold region when the FSS becomes practically transparent, which is an interesting feature with potential applications.

Revista Principia, Dec 2, 2015

&amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;gt;Este trabalho te... more &amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;gt;Este trabalho teve como objetivo o desenvolvimento de uma antena com pequenas dimensões que atue na faixa de frequência utilizada pelo sistema de quarta geração de telefonia móvel (4G) – 2,5 GHz a 2,69 GHz. As simulações foram realizadas utilizando o software comercial Ansoft Designer. A estrutura escolhida para a simulação foi uma antena planar, que devido a algumas de suas características – tais como baixo perfil, pequenas dimensões e custo reduzido –, é importante para sistemas que demandam conectividade aliada à mobilidade, como é o caso do sistema 4G.&amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;gt;

In this paper a frequency selective surface, FSS, based on open trapezoidal rings geometry is pre... more In this paper a frequency selective surface, FSS, based on open trapezoidal rings geometry is presented. Composed of four independent open rings, the geometry's characteristics are described and its frequency response discussed, including the polarization effects and how the pairs of rings are excited. Initial project equations are proposed for the first two resonant frequencies. Although these equations are an approximation, a first step for a numerical optimization, differences less than 6% were obtained, when compared to measured resonant frequencies. One advantage of the proposed FSS is the possibility of adjust almost separately the frequency response associated to each pair of open trapezoidal rings. Four FSS were fabricated and characterized, with numerical and measured results verifying a very good agreement. The ease of design, the achieved results, as well the possibility of integrating the open trapezoidal rings with other geometries, instigate the use of the proposed FSS in application such as smart electromagnetic buildings, reconfigurable FSS and so forth.

This paper reports the analysis of U-slot rectangular patch FSS. The numerical results were obtai... more This paper reports the analysis of U-slot rectangular patch FSS. The numerical results were obtained using the Wave Concept Iterative Procedure, WCIP. Initially, a conventional rectangular patch is considered and after a single slot is inserted. Then, the U-slot arms are increased and the frequency behavior discussed. In order to validate the numerical results, three FSS were selected, fabricated and experimentally characterized. When compared to simulations, the experimental results present a very good agreement. Considering conventional rectangular patch, the reduction of first frequency of resonance achieve up 63.2%. The proposed FSS frequency behavior may be suitable in the design of multiband structures. In addition, the reduction of the first frequency of resonance also implies miniaturization advantages. These characteristics instigates other research groups to pursuit this investigation.

VII CONNEPI - Congresso Norte Nordeste de Pesquisa e Inovação, Aug 15, 2012

Nos dias atuais, ha um aumento na demanda por dispositivos moveis e/ou portateis, como notebook e... more Nos dias atuais, ha um aumento na demanda por dispositivos moveis e/ou portateis, como notebook e tablet . Esse interesse surgiu principalmente pelo aumento da quantidade de servicos que utilizam sistemas de comunicacao sem fio (ou wireless ). Uma tendencia do mercado e a integracao de diferentes tecnologias sem fio em um unico dispositivo portatil, de baixo custo, com design leve e compacto. Este trabalho tem como objetivo o desenvolvimento de uma antena com pequenas dimensoes (mas com eficiencia aceitavel) e que atue na faixa de frequencia para aplicacoes em TV digital (470 a 806 MHz). As simulacoes foram realizadas utilizando o software comercial Ansoft HFSS ( High Frequency Structure Simulator ), que utiliza o metodo numerico das diferencas finitas. A estrutra escolhida para a simulacao foi uma antena de microfita planar. Os resultados obtidos, a partir das simulacoes, apontam para a eficiencia do processo de miniaturizacao (insercao de fendas) empregado na antena, permitindo a mesma funcionar na faixa de frequencia utilizada pela aplicacao de TV Digital.