Paulo Henrique da Fonseca Silva

A new FSS design proposal for UWB applications

This work presents a new proposal for Frequency Selective Surface (FSS) design for Ultra-Wideband (UWB) applications. The new FSSs consist of an array composed by the association of two patch elements per cell: a square loop and a crossed dipole. These structures are called Crossed Loops and have the objective of increasing the bandwidth of the square loop and the crossed dipole, when analyzed separately. Simulated results of the transmission coefficients are obtained using the Ansoft Designer¿ commercial software. Some of the FSSs tested were fabricated in order to make an experimental analysis with the measured results and to validate the new proposal. In particular, the presented results for the transmission coefficient of a built FSS prototype indicate a percent bandwidth 52.4%.

Blending PSO and ANN for Optimal Design of FSS Filters With Koch Island Patch Elements

This work presents a new fast and accurate electromagnetic (EM) optimization technique blending the Particle Swarm Optimization (PSO) algorithm and a Multilayer Perceptrons (MLP) Artificial Neural Network (ANN). The proposed technique was applied for optimal design of Koch fractal Frequency Selective Surface (FSS) with desired stop-band filter specification. Initially, a full-wave parametric analysis was carried out for accurate EM-characterization of FSS filters. From obtained EM-dataset, a MLP network was trained with the first-order Resilient Backpropagation (RPROP) algorithm. The developed MLP model for FSS synthesis was used for efficient evaluation of cost function in PSO iterations. The advantages in the optimal design of FSS through the PSO-ANN technique were discussed in terms of convergence and computational cost. Two optimized FSS prototypes were built and measured. The accuracy of the proposed optimization technique was verified through the excellent agreement obtained by means of comparisons between theoretical and experimental results.

A comparative study of three ultra-wideband log-periodic microstrip antenna arrays

This paper described the design, simulation and fabrication of three ultra-wideband log-periodic microstrip antenna arrays. A comparative study is presented between arrays using rectangular, square and circular patch elements and varying the number of elements (5, 10 e 15). Electromagnetically coupled microstrip patches had been used as radiating element of arrays. The frequency responses of these arrays are analysed using the Ansoft Designer¿ commercial software that implements the method of moments. After the simulations were completed, three prototypes were constructed and measured using a vector network analyzer. The results for the -10 dB return loss bandwidth of the antenna arrays are presented. The good agreement between theoretical and experimental results for the built antenna prototypes validated the used methodology.

A compact frequency selective surface with angular stability based on the Sierpinski fractal geometry

The Sierpinski fractal geometry is used to design frequency-selective surface (FSS) band-stop filters for microwave applications. The design’s main goals are FSS structure size compactness and angular stability at the resonant frequencies, as well as dual-band and dual-polarized performance. The proposed FSS structure is composed of a periodic array of fractal patch elements printed on a dielectric substrate layer. A parametric investigation of the FSS frequency response is accomplished to find out the effect of the fractal patch element’s cell size and iteration-number (level). Tuning possibilities are observed at the FSS resonance bands when the fractal patch element level is increased. To validate the used methodology, three prototypes are built and measured in the frequency range from 3.0 to 14 GHz. It is shown that the proposed FSS structure presents the spatial filters’ most desired characteristics such as compactness, with high frequency compression factor values (up to 66.08%), dual-polarization, and excellent angular stability.

Simple, Compact, and Multiband Frequency Selective Surfaces Using Dissimilar Sierpinski Fractal Elements

This paper presents a design methodology for frequency selective surfaces (FSSs) using metallic patches with dissimilar Sierpinski fractal elements. The transmission properties of the spatial filters are investigated for FSS structures composed of two alternately integrated dissimilar Sierpinski fractal elements, corresponding to fractal levels , 2, and 3. Two FSS prototypes are fabricated and measured in the range from 2 to 12 GHz to validate the proposed fractal designs. The FSSs with dissimilar Sierpinski fractal patch elements are printed on RT/Duroid 6202 high frequency laminate. The experimental characterization of the FSS prototypes is accomplished through two different measurement setups composed of commercial horns and elliptical monopole microstrip antennas. The obtained results confirm the compactness and multiband performance of the proposed FSS geometries, caused by the integration of dissimilar fractal element. In addition, the proposed FSSs exhibited frequency tuning ability on the multiband frequency responses. Agreement between simulated and measured results is reported.

Analysis and design of frequency selective surfaces using teragon patch elements for WLAN applications

This paper describes a fractal design methodology for frequency selective surfaces (FSSs) composed of teragon metallic patches on a single-layer fiberglass dielectric. Shapes presented by teragons are exploited to design compact FSSs acting as dual-band band-stop spatial filters. An FSS parametric analysis is performed in terms of the fractal dimension and unit cell size of fractal patches. The transmission properties of the proposed periodic arrays are initially investigated through simulations performed by Ansoft DesignerTM commercial software. To validate the used methodology, three FSS prototypes are selected for fabrication, and one of them is designed to reject wireless local area network signals in the bands of 2.4–2.5 GHz (IEEE 802.11b) and 5.0–6.0 GHz (IEEE 802.11a). Experimental characterization of the FSS prototypes is accomplished through an alternative setup with elliptical monopole microstrip antennas for low-cost FSS measurements. The obtained results point to interesting features for FSS spatial filters: compactness, with high values of frequency compression factor (up to 80.4%); dual polarization; dual-band frequency responses; and stable resonance frequencies at oblique incidence.

A new configuration of planar monopole quasi-fractal antenna for wireless communications

An investigation of the bandwidth behavior of planar monopoles built with quasi-fractal patches based on the curves of Koch is presented. A rectangular monopole patch microstrip antenna is used as reference and generator for the proposed quasi-fractals antennas. Koch levels 1 and 2 geometries are developed. The analysis of the antenna structures is performed using Ansoft HFSS™. Prototypes are built to compare simulated and measured results.

Bio-inspired antenna for UWB systems

In this paper is presented a new printed monopole antenna, bio-inspired by jasmine flower, that meets the Federal Communications Commission parameters for ultra-wideband systems. The design of the printed monopole antenna in jasmine flower has developed from a printed monopole antenna with circular geometry, with comparison results. The measured results of bio-inspired antenna in the jasmine flower showed compatibility with the parameters required by the FCC for ultra-wideband technology. It obtained bandwidth of 9.75 GHz, half-power beamwidth of 148 degrees, omnidirectional radiation pattern, gain of 5.99 dBi, power spectral density below -41.3 dBm across the bandwidth of ultra-wideband technology, small pulse distortion, and constant group delay, with variations of less than 2ns.

Arrays of rectangular patch microstrip antennas for aerospace applications

This work presents an investigation on the performance of rectangular microstrip antenna arrays with m×n rectangular patch elements. Several rectangular antenna array geometries are investigated namely 2×1, 1×2, 2×2, 2×4 and 4×2 for aerospace microwave applications. Simulations are performed using Ansoft HFSS commercial software. Simulated results are shown for the antenna arrays return loss, resonant frequencies, bandwidth, and gain, taking into account the array geometry and number of patch elements. To validate the simulated results, several prototypes are built and measured. Agreement is observed between simulation and measurement results.

Analysis of frequency selective surfaces with T-shaped pre-fractals patch elements

This paper presents an analysis of spectral behavior in frequency selective surfaces (FSS). In these structures, which act as stop-band filters, T-shaped fractal patch elements with different levels were inserted. The analysis of new FSS configurations is performed using Ansoft Designer™ software. The proposed structures are composed by a 2-D periodic array of metal pre-fractals elements printed on a dielectric substrate. Some prototypes were built and measured to validate the theoretical results.