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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.

Full-Wave Analysis of Stable Cross Fractal Frequency Selective Surfaces Using an Iterative Procedure Based on Wave Concept

This work presents a full-wave analysis of stable frequency selective surfaces (FSSs) composed of periodic arrays of cross fractal patch elements. The shapes of these patch elements are defined conforming to a fractal concept, where the generator fractal geometry is successively subdivided into parts which are smaller copies of the previous ones (defined as fractal levels). The main objective of this work is to investigate the performance of FSSs with cross fractal patch element geometries including their frequency response and stability in relation to both the angle of incidence and polarization of the plane wave. The frequency response of FSS structures is obtained using the wave concept iterative procedure (WCIP). This method is based on a wave concept formulation and the boundary conditions for the FSS structure. Prototypes were manufactured and measured to verify the WCIP model accuracy. A good agreement between WCIP and measured results was observed for the proposed cross fractal FSSs. In addition, these FSSs exhibited good 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.

Iterative Full-Wave Analysis of Mandelbrot-Inspired Fractal Patch Antenna on Textile Substrate for UWB Applications

This work presents the analysis of monopole microstrip antennas with truncated ground plane and patch geometry inspired on the Mandelbrot fractal curve for applications in UWB systems. The proposed antenna geometry is analyzed using the Wave Concept Iterative Procedure (WCIP), a full-wave method. Results for the proposed antenna operating frequency, bandwidth, VSWR, gain, and radiation pattern are obtained and discussed. The WCIP results are compared with simulation results provided by HFSS software, for validation purpose. In addition, a prototype antenna is built and measured. A good match between WCIP theoretical and simulation, HFSS simulation, and measurement results is observed for the antenna frequency response.

Application of Bio-Inspired Algorithms and Neural Networks for Optimal Design of Fractal Frequency Selective Surfaces

Technological advances in the field of microwave and communication systems and the increase of their commercial applications in recent years have resulted in more stringent requirements for innovative design of microwave passive devices, such as: antennas, filters, power splitters and couplers, frequency selective surfaces, etc. To be competitive in the commercial marketplace, microwave engineers may be using computer-aided design (CAD) tools to minimize cost and design cycle times. Modern CAD tools have become an integral part of the microwave product cycle and demand powerful optimization techniques combined with fast and accurate models so that the optimal solutions can be achieved, eventually guaranteeing first-pass design success. The target of microwave device design is to determine a set of physical parameters to satisfy certain design specifications (Mohamed, 2005).

Software for project and analysis of frequency selective surfaces

In this paper, a software for design and analysis of frequency selective surfaces (FSS) based on the equivalent circuit model is presented, with emphasis on teaching students in the interaction between FSS parameters. Tools to design FSSs and a tutorial with theoretical elements of the equivalent circuit method, applied to FSS, compose this software. The software can be used at FSS analysis and design course to consolidate the first theoretical and illustrated concepts.