2019 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2019
The magnetic tuning of a dual-frequency cylindrical magneto-dielectric antenna based on the YIG m... more The magnetic tuning of a dual-frequency cylindrical magneto-dielectric antenna based on the YIG matrix was studied. The antenna resonates at two frequency bands, 5.77 GHz and 6.74 GHz. An experimental analysis was carried out using an external magnetic field on the antenna to observe the tuning effect in the resonant frequencies as a function of the applied external magnetic field. And we observed an effect on bandwidth and impedance matching of the antenna. As the magnetic field increased, the bandwidth decreased. The tuning results at both resonant frequencies are presented and discussed.
As subestações concentram equipamentos essenciais para o funcionamento das redes de distribuição ... more As subestações concentram equipamentos essenciais para o funcionamento das redes de distribuição de energia elétrica. O diagnóstico do estado de degradação dos equipamentos é muito importante, em especial dos disjuntores que são os responsáveis por seccionar a rede. Uma técnica que tem se destacado é o diagnóstico de disjuntores a partir da análise do sinal irradiado pelo arco elétrico, que ocorre na comutação de estados nos disjuntores. Essa técnica compreende a captação do sinal irradiado, seu armazenamento em formato digital, e análise a partir de informações obtidas. Um problema que essa técnica enfrenta é a otimização dos cenários de medições, pois para isso é necessário estar em uma subestação, onde as comutações são realizadas sem controle dos pesquisadores, ou possuir disjuntores em laboratório. Porém, em laboratório existem limitações quanto aos tipos de disjuntores pela impossibilidade de ter vários disjuntores em laboratório. A metodologia de otimização proposta neste art...
This article presents the implementation of a dual band FSS for intelligent walls applications, c... more This article presents the implementation of a dual band FSS for intelligent walls applications, covering the WiFi frequency bands, 2.4 GHz and 5.8 GHz. The four arms star geometry, associated to trapezoidal rings, are used, which allows a more flexible frequency response adjust. Initial project equations are introduced and the frequency response characteristics discussed. Numerical and measured results are presented for four FSS, verifying a good agreement, achieving, for the x polarization, a transmission coefficient of, at least, 15 dB of atenuation for each WiFi band. Keywords— FSS, intelligent walls, WiFi.
2015 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2015
A band pass frequency selective surface, FSS, using the slot four arms star geometry is proposed ... more A band pass frequency selective surface, FSS, using the slot four arms star geometry is proposed in this paper. The design procedure used to obtain the slot four arms star geometry is described and an expression to estimate the first resonance frequency is presented. In order to numerically characterize the FSS, the commercial software ANSYS Designer, based on the Method of Moments, was employed and the frequency response of four slot arms star with width of 10 mm, 12 mm, 14 mm and 16 mm are presented and discussed. The band pass behaviour is verified and the resonance frequencies shown a very good agreement when compared to the obtained by using the proposed expression. Four FSS were experimentally characterized and the obtained results shown a very good agreement when compared to the simulated ones. The achieved characteristics of the FSS frequency response and its simplicity makes the slot four arms star a useful geometry for applications where a band pass behaviour is requested.
In this work, simulations and measurements are presented to the FSS with fractal elements, more s... more In this work, simulations and measurements are presented to the FSS with fractal elements, more specifically, Koch Island elements. The wave concept iterative procedure, WCIP, is employed to the simulations and the obtained results are compared to measured ones and to those obtained by the use of Ansoft Designer™ commercial software. Beyond these results, the behaviour of the electromagnetic fields and polarization effects are discussed. The contribution of some fractal details is questioned.
Resumo-Neste artigo é apresentado o desenvolvimento de um filtro rejeita faixa compacto com reduz... more Resumo-Neste artigo é apresentado o desenvolvimento de um filtro rejeita faixa compacto com reduzida banda de transição para aplicação na faixa de 2,4 GHz. O filtro proposto baseia-se na geometria matrioska, possibilitando uma considerável miniaturização. A geometria matrioska é descrita e são propostas equações iniciais de projeto, com as quais é possível estimar as frequências de ressonâncias. São comparados filtros em C, com um ressonador com dois anéis matrioskas, com dois ressonadores em série e, concluindo, um filtro que fica praticamente contido na linha de alimentação. São apresentados resultados numéricos e experimentais, observando-se uma boa concordância entre os mesmos.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2021
A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geome... more A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geometries is described in this paper. The proposed reconfigurable FSS uses as active element PIN diodes. With the associated geometries, three resonant frequencies are achieved, two fixed, related to the matryoshka geometry, and one that can be activated or not, related to the cross dipoles geometry. Differently from previous works, an inductor was inserted into the cross dipoles' horizontal arms, maintaining its resonance for polarization. The PIN diode inserted into cross dipoles' vertical arms controls the respective resonance. The design procedures for each geometry, in addition to PIN diode and RF inductor basics are outlined. The expected results are discussed based on the analysis of the resonances of each geometry and the associated geometries, as well as the different PIN diode bias states (OFF and ON). A prototype was fabricated and characterized, obtaining a good agreement between the numerical and experimental results, with a reconfiguration bandwidth of. , from. to. , for a variation of at least 푩 between the OFF and ON states. Index Terms-Cross dipoles, matryoshka, PIN diode, reconfigurable FSS. I. INTRODUCTION With increasing number of users and diversity of services, telecommunications systems, especially mobile communication systems, use the frequency spectrum more and more intensively. Artificial intelligence (AI), cloud-based computing, Internet of Things (IoT), big data, cyber security and resilience, robotic process automation and fifth-generation mobile communications system (5G) are just some examples of the existing demands, requiring an adequate management of the radio frequency spectrum, imposing restrictions both in the frequency bands to be used, as in the power levels [1]. These restrictions have required new solutions, such as reconfigurable antennas [2]-[4] and electromagnetically intelligent buildings [5], [6], in order to optimize the use of the spectrum and minimize interference. In the implementation of reconfigurable antennas, as well as electromagnetically intelligent buildings, one of the adopted approaches is the use of frequency selective surfaces, FSS, in its
2017 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications (APWC), 2017
This paper presents a proposal for the modification of the Elitist Non-dominated Sorting Genetic ... more This paper presents a proposal for the modification of the Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) whose operation is based on the concepts of dominance found in the principle of Pareto efficiency. The proposed modification is about the domain to be analyzed by the algorithm, which is then restricted to a region near the point of interest, thus being faster and with a lower computational cost due to the smaller search space.
This work presents the analysis of the tapered microstrip patch antenna by the Wave Concept Itera... more This work presents the analysis of the tapered microstrip patch antenna by the Wave Concept Iterative Procedure, WCIP. The resonant frequencies variation with the patch dimensions and how to include it as project flexibility is discussed. The behavior of the electric fields is presented and analyzed for the first two resonant frequencies. Numerical and measured results are compared and a good agreement is observed.
Microwave and Optoelectronics SBMO/IEEE MTT-S International Conference, 2011
This paper proposes the use of the wave concept iterative procedure, or WCIP method, for the char... more This paper proposes the use of the wave concept iterative procedure, or WCIP method, for the characterization of RFID tag antennas for microwave applications. The WCIP method has been considered as a very attractive alternative to the solution of electromagnetic problems due to its simplicity and accuracy. Numerical results for the considered tag antennas are compared to those obtained by
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
A Defected Ground Structure, DGS, based on matryoshka geometry is described in this paper. The pr... more A Defected Ground Structure, DGS, based on matryoshka geometry is described in this paper. The proposed DGS geometry is outlined and initial design equations are presented. Four prototypes, with resonant frequencies 2.17 GHz, 2.44 GHz, 2.99 GHz and 3.73 GHz, were designed, fabricated and characterized, observing a good agreement between measured and numerical results. Also, the obtained results demonstrated the initial design equations usefulness. The resonant behavior was analyzed in terms of the current density and it is possible to observe the current density blocked at the resonant frequency. When compared with dumbbell DGS, a reduction in the resonant frequency up to 47.19% is achieved, confirming the matryoshka geometry miniaturization properties. Furthermore, still comparing with dumbbell geometry, DGS based on matryoshka geometry are more selective.
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.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioin... more This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioinspired computing and a general regression neural network (GRNN). This hybrid computational method, which utilizes the multi-objective cuckoo search algorithm combined to a GRNN, determine the best physical dimensions of the FSS in order to achieve a multi-band filtering at the 2.4, 3.5 and 5.8 GHz spectrums. Therefore, the results are to be applied to aid the propagation of Wi-Fi, WLAN, WiMAX and future sub-6 GHz 5G systems. The resonant frequencies were measured and a-10 dB cutoff value has been considered for the transmission coefficient. The triple rectangular loop conductor geometry of the device is printed upon a glass epoxy (FR-4) substrate. Measurements were made for different wave incidence angles, from 0°up to 45°, to demonstrate how signal incidence would affect the device's functioning. The agreement between simulated and measured data display satisfactory results.
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.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
In this paper, the authors present a proposal for an application of electromagnetic bandgap (EBG)... more In this paper, the authors present a proposal for an application of electromagnetic bandgap (EBG), for suppression of grating lobes, in frequency selective surfaces (FSS), not yet studied in the literature. An alternative type of EBG with square holes was proposed to reduce the computational effort in simulations. The study consists of an application of a rectangular periodic array of cylindrical and square holes in FSS dielectric substrate to create rejection bands and suppress specific resonant frequency modes. We built four prototypes and compared measured results with simulated results obtained with ANSYS HFSS. Simulations and measurements show suppression levels up to 6 dB. A good agreement between the results is observed. The FSS with EBG with square holes allows a simulation time 70 % lower than FSS with EBG with cylindrical holes.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
A modeling of the resonant behavior of a continuously reconfigurable frequency selective surface,... more A modeling of the resonant behavior of a continuously reconfigurable frequency selective surface, FSS, is described in this paper. The FSS is based on four arms star geometry and its reconfigurability is achieved by the use of varactors. FSS, four arms star geometry and varactor principles are explained. Considering available a set of measured or numerical data, with frequency responses for different varactor capacitance values, the FSS equivalent circuit is stablished. Then, the varactor capacitance effect is included and the resonant behavior can be easily determined. After stablished, the FSS equivalent circuit can be applied even for a different varactor. In order to validate the proposed modeling, the equivalent circuit of a reconfigurable FSS using the varactor SMV1231 (. ≤ ≤ .) is obtained. The equivalent circuit results are compared to numerical (ANSYS) and measured results, verifying a good agreement. Following, for the same geometry, the equivalent circuit is applied to a reconfigurable FSS using the SMV1234 varactor (. ≤ ≤ .) and once more a good agreement between the results is observed, indicating the applicability of the proposed modeling, which is especially attractive for optimization process.
2019 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2019
The magnetic tuning of a dual-frequency cylindrical magneto-dielectric antenna based on the YIG m... more The magnetic tuning of a dual-frequency cylindrical magneto-dielectric antenna based on the YIG matrix was studied. The antenna resonates at two frequency bands, 5.77 GHz and 6.74 GHz. An experimental analysis was carried out using an external magnetic field on the antenna to observe the tuning effect in the resonant frequencies as a function of the applied external magnetic field. And we observed an effect on bandwidth and impedance matching of the antenna. As the magnetic field increased, the bandwidth decreased. The tuning results at both resonant frequencies are presented and discussed.
As subestações concentram equipamentos essenciais para o funcionamento das redes de distribuição ... more As subestações concentram equipamentos essenciais para o funcionamento das redes de distribuição de energia elétrica. O diagnóstico do estado de degradação dos equipamentos é muito importante, em especial dos disjuntores que são os responsáveis por seccionar a rede. Uma técnica que tem se destacado é o diagnóstico de disjuntores a partir da análise do sinal irradiado pelo arco elétrico, que ocorre na comutação de estados nos disjuntores. Essa técnica compreende a captação do sinal irradiado, seu armazenamento em formato digital, e análise a partir de informações obtidas. Um problema que essa técnica enfrenta é a otimização dos cenários de medições, pois para isso é necessário estar em uma subestação, onde as comutações são realizadas sem controle dos pesquisadores, ou possuir disjuntores em laboratório. Porém, em laboratório existem limitações quanto aos tipos de disjuntores pela impossibilidade de ter vários disjuntores em laboratório. A metodologia de otimização proposta neste art...
This article presents the implementation of a dual band FSS for intelligent walls applications, c... more This article presents the implementation of a dual band FSS for intelligent walls applications, covering the WiFi frequency bands, 2.4 GHz and 5.8 GHz. The four arms star geometry, associated to trapezoidal rings, are used, which allows a more flexible frequency response adjust. Initial project equations are introduced and the frequency response characteristics discussed. Numerical and measured results are presented for four FSS, verifying a good agreement, achieving, for the x polarization, a transmission coefficient of, at least, 15 dB of atenuation for each WiFi band. Keywords— FSS, intelligent walls, WiFi.
2015 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2015
A band pass frequency selective surface, FSS, using the slot four arms star geometry is proposed ... more A band pass frequency selective surface, FSS, using the slot four arms star geometry is proposed in this paper. The design procedure used to obtain the slot four arms star geometry is described and an expression to estimate the first resonance frequency is presented. In order to numerically characterize the FSS, the commercial software ANSYS Designer, based on the Method of Moments, was employed and the frequency response of four slot arms star with width of 10 mm, 12 mm, 14 mm and 16 mm are presented and discussed. The band pass behaviour is verified and the resonance frequencies shown a very good agreement when compared to the obtained by using the proposed expression. Four FSS were experimentally characterized and the obtained results shown a very good agreement when compared to the simulated ones. The achieved characteristics of the FSS frequency response and its simplicity makes the slot four arms star a useful geometry for applications where a band pass behaviour is requested.
In this work, simulations and measurements are presented to the FSS with fractal elements, more s... more In this work, simulations and measurements are presented to the FSS with fractal elements, more specifically, Koch Island elements. The wave concept iterative procedure, WCIP, is employed to the simulations and the obtained results are compared to measured ones and to those obtained by the use of Ansoft Designer™ commercial software. Beyond these results, the behaviour of the electromagnetic fields and polarization effects are discussed. The contribution of some fractal details is questioned.
Resumo-Neste artigo é apresentado o desenvolvimento de um filtro rejeita faixa compacto com reduz... more Resumo-Neste artigo é apresentado o desenvolvimento de um filtro rejeita faixa compacto com reduzida banda de transição para aplicação na faixa de 2,4 GHz. O filtro proposto baseia-se na geometria matrioska, possibilitando uma considerável miniaturização. A geometria matrioska é descrita e são propostas equações iniciais de projeto, com as quais é possível estimar as frequências de ressonâncias. São comparados filtros em C, com um ressonador com dois anéis matrioskas, com dois ressonadores em série e, concluindo, um filtro que fica praticamente contido na linha de alimentação. São apresentados resultados numéricos e experimentais, observando-se uma boa concordância entre os mesmos.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2021
A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geome... more A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geometries is described in this paper. The proposed reconfigurable FSS uses as active element PIN diodes. With the associated geometries, three resonant frequencies are achieved, two fixed, related to the matryoshka geometry, and one that can be activated or not, related to the cross dipoles geometry. Differently from previous works, an inductor was inserted into the cross dipoles' horizontal arms, maintaining its resonance for polarization. The PIN diode inserted into cross dipoles' vertical arms controls the respective resonance. The design procedures for each geometry, in addition to PIN diode and RF inductor basics are outlined. The expected results are discussed based on the analysis of the resonances of each geometry and the associated geometries, as well as the different PIN diode bias states (OFF and ON). A prototype was fabricated and characterized, obtaining a good agreement between the numerical and experimental results, with a reconfiguration bandwidth of. , from. to. , for a variation of at least 푩 between the OFF and ON states. Index Terms-Cross dipoles, matryoshka, PIN diode, reconfigurable FSS. I. INTRODUCTION With increasing number of users and diversity of services, telecommunications systems, especially mobile communication systems, use the frequency spectrum more and more intensively. Artificial intelligence (AI), cloud-based computing, Internet of Things (IoT), big data, cyber security and resilience, robotic process automation and fifth-generation mobile communications system (5G) are just some examples of the existing demands, requiring an adequate management of the radio frequency spectrum, imposing restrictions both in the frequency bands to be used, as in the power levels [1]. These restrictions have required new solutions, such as reconfigurable antennas [2]-[4] and electromagnetically intelligent buildings [5], [6], in order to optimize the use of the spectrum and minimize interference. In the implementation of reconfigurable antennas, as well as electromagnetically intelligent buildings, one of the adopted approaches is the use of frequency selective surfaces, FSS, in its
2017 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications (APWC), 2017
This paper presents a proposal for the modification of the Elitist Non-dominated Sorting Genetic ... more This paper presents a proposal for the modification of the Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) whose operation is based on the concepts of dominance found in the principle of Pareto efficiency. The proposed modification is about the domain to be analyzed by the algorithm, which is then restricted to a region near the point of interest, thus being faster and with a lower computational cost due to the smaller search space.
This work presents the analysis of the tapered microstrip patch antenna by the Wave Concept Itera... more This work presents the analysis of the tapered microstrip patch antenna by the Wave Concept Iterative Procedure, WCIP. The resonant frequencies variation with the patch dimensions and how to include it as project flexibility is discussed. The behavior of the electric fields is presented and analyzed for the first two resonant frequencies. Numerical and measured results are compared and a good agreement is observed.
Microwave and Optoelectronics SBMO/IEEE MTT-S International Conference, 2011
This paper proposes the use of the wave concept iterative procedure, or WCIP method, for the char... more This paper proposes the use of the wave concept iterative procedure, or WCIP method, for the characterization of RFID tag antennas for microwave applications. The WCIP method has been considered as a very attractive alternative to the solution of electromagnetic problems due to its simplicity and accuracy. Numerical results for the considered tag antennas are compared to those obtained by
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
A Defected Ground Structure, DGS, based on matryoshka geometry is described in this paper. The pr... more A Defected Ground Structure, DGS, based on matryoshka geometry is described in this paper. The proposed DGS geometry is outlined and initial design equations are presented. Four prototypes, with resonant frequencies 2.17 GHz, 2.44 GHz, 2.99 GHz and 3.73 GHz, were designed, fabricated and characterized, observing a good agreement between measured and numerical results. Also, the obtained results demonstrated the initial design equations usefulness. The resonant behavior was analyzed in terms of the current density and it is possible to observe the current density blocked at the resonant frequency. When compared with dumbbell DGS, a reduction in the resonant frequency up to 47.19% is achieved, confirming the matryoshka geometry miniaturization properties. Furthermore, still comparing with dumbbell geometry, DGS based on matryoshka geometry are more selective.
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.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioin... more This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioinspired computing and a general regression neural network (GRNN). This hybrid computational method, which utilizes the multi-objective cuckoo search algorithm combined to a GRNN, determine the best physical dimensions of the FSS in order to achieve a multi-band filtering at the 2.4, 3.5 and 5.8 GHz spectrums. Therefore, the results are to be applied to aid the propagation of Wi-Fi, WLAN, WiMAX and future sub-6 GHz 5G systems. The resonant frequencies were measured and a-10 dB cutoff value has been considered for the transmission coefficient. The triple rectangular loop conductor geometry of the device is printed upon a glass epoxy (FR-4) substrate. Measurements were made for different wave incidence angles, from 0°up to 45°, to demonstrate how signal incidence would affect the device's functioning. The agreement between simulated and measured data display satisfactory results.
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.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
In this paper, the authors present a proposal for an application of electromagnetic bandgap (EBG)... more In this paper, the authors present a proposal for an application of electromagnetic bandgap (EBG), for suppression of grating lobes, in frequency selective surfaces (FSS), not yet studied in the literature. An alternative type of EBG with square holes was proposed to reduce the computational effort in simulations. The study consists of an application of a rectangular periodic array of cylindrical and square holes in FSS dielectric substrate to create rejection bands and suppress specific resonant frequency modes. We built four prototypes and compared measured results with simulated results obtained with ANSYS HFSS. Simulations and measurements show suppression levels up to 6 dB. A good agreement between the results is observed. The FSS with EBG with square holes allows a simulation time 70 % lower than FSS with EBG with cylindrical holes.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
A modeling of the resonant behavior of a continuously reconfigurable frequency selective surface,... more A modeling of the resonant behavior of a continuously reconfigurable frequency selective surface, FSS, is described in this paper. The FSS is based on four arms star geometry and its reconfigurability is achieved by the use of varactors. FSS, four arms star geometry and varactor principles are explained. Considering available a set of measured or numerical data, with frequency responses for different varactor capacitance values, the FSS equivalent circuit is stablished. Then, the varactor capacitance effect is included and the resonant behavior can be easily determined. After stablished, the FSS equivalent circuit can be applied even for a different varactor. In order to validate the proposed modeling, the equivalent circuit of a reconfigurable FSS using the varactor SMV1231 (. ≤ ≤ .) is obtained. The equivalent circuit results are compared to numerical (ANSYS) and measured results, verifying a good agreement. Following, for the same geometry, the equivalent circuit is applied to a reconfigurable FSS using the SMV1234 varactor (. ≤ ≤ .) and once more a good agreement between the results is observed, indicating the applicability of the proposed modeling, which is especially attractive for optimization process.
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Papers by Alfredo Gomes