Design of dual-polarised multiband frequency selectivesurfaces using fractal elements

Fractal geometries have been extensively implemented in the design of multiband antenna and frequency selective surface (FSS). For example, convoluted and Hilbert patch elements were first proposed to reduce the unit cell size of FSS (Parker and El Sheikh, IEE Proc.-H, 138, 19–22, 1991.) A fractal FSS with self-similar Sierpinski dipole array was shown to have two stop bands (J. Romeu and Y. Rahmat-Samii, IEEE Trans., AP-48, 1097–1104, 2000). However, its resonant frequencies are rather sensitive to incident angles and polarizations. Minkowski patch FSS and Sierpinski carpet fractals have been shown to provide two or three stop bands with dual polarization capability (J.P. Gianvittorio, et. al., IEEE Trans., AP-51, 3088–3096, 2003.) Recently miniature band-pass FSS with fractal antenna-filter-antenna arrays was designed and demonstrated with good frequency selectivity (S. Zheng, et. al., IEEE AWPL, 11, 240–243, 2012.) A dual band fractal FSS with a 3:1 reflection to pass band ratio and significantly improved resonant frequency stability was proposed by the author (T.K. Wu, Microwave Optical Tech. Letters, 54, 833–835, 2012).

A novel frequency selective surfaces (FSS) based on Y-loop fractal element is investigated using finite difference frequency domain (FDFD) method and verified with experiment in this paper. Numerical and experiment results show that the Y-loop fractal FSS has the advantages of low insertion loss in pass-band, good frequency selectivity and stability of bandwidth etc. Its performance is very stable at various incident angles and different polarization state. Besides, because over 90% of the surface covered with metal, the Y-loop fractal FSS obtains very high IR reflectivity, so the proposed FSS can also be used in MMW/IR compound system as dichroic beam combiner.

This work presents an electromagnetic optimization technique that blending full-wave method, artificial neural network, and population-based search algorithms for optimal design of frequency selective surfaces (FSSs) with fractal motifs. We consider a simple application of this technique in a single-layer FSS with Sierpinski island fractal patch elements. The optimization technique replaces the computational intensive full-wave method of moments simulations by a fast and accurate multilayer perceptrons neural network model of FSS spatial filter, which is used to compute the cost (or fitness) function in the search algorithms iterations. In the FSS optimization with specific resonant frequency and bandwidth, we use: bees algorithm, continuous genetic algorithm, and particle swarm optimization. A FSS prototype is built and measured for a first level of Sierpinski island fractal. The accuracy of the proposed optimization technique is verified through the excellent agreement (0.9%) obtained by means of comparisons between theoretical and experimental results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:827–831, 2014

In order to make the dual-band frequency-selective surface (FSS) used in the engineering conditions of thick substrate, wide band spacing and large incident angle, an FSS structure with dual-band at Ku-band and Ka-band is presented. The stable filtering condition of the FSS is analyzed by using the grating lobe diagram, and the transmission of the FSS with combination or fractal elements is calculated using the vector modal matching method. The design method of the dual-band FSS with thick substrate is obtained by analyzing the resonance mode of the element and the transmission of the FSS. By using those methods, an FSS with combination elements of the square and Y loops is designed. The simulated and tested results show that the dual-bands of the structure at Ku-band and Ka-band are stable and the transmissions of the two pass-bands are larger than 75% when the incident angle is varied from normal to 45. This paper provides some theoretical and experimental references for the design of the dual-band FSS with thick substrate, wide band spacing and large incident angle.

This work proposes the inverse design of bandstop Frequency Selective Surface using a Graph based Conditional Variational Autoencoder (G-CVAE) integrated with a Physics-Informed Neural Network (PINN). This inverse design involves the prediction of FSS geometry that exhibits ultra-wide stopband characteristics. Initially, the graph convolutional network precisely extracts the topological and spatial relationships within the FSS geometrical design. The features of the graph and simulation results of the FSS dataset are used to train the CVAE, which maps the FSS physical structure and its electromagnetic behavior. The trained CVAE predicts the FSS geometries with desired frequency responses, while the PINN is incorporated to ensure physical feasibility. By monitoring the average relative error values, the simulated and predicted transmission coefficients are brought closer to each other. Also, similar approach is followed to enhance the angular stability and to achieve polarization independence in both TE and TM modes. A G-CVAE-PINN is constructed and trained using various random combinations of graph attributes and simulation outcomes, achieving an average inaccuracy of 3%. Further, one of the best designs from the predicted FSS designs is chosen for experimental validation. This predicted and experimentally validated bandstop FSS exhibits wide band rejection of 20 GHz ranging from 8 GHz to 28 GHz. The fabricated design exhibits polarization independence up to 75°in both normal and oblique angles. Thus, the predicted FSS designs are ideal for radome, EMI shielding, and satellite communications, providing efficient frequency filtering for 5G and beyond 5G networks.

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 levelsk=1, 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.

This work reveals the Design and development of Dual wide band frequency selective surfaces (FSS). Dual-band FSS based on single and multi layers with or without or extra discrete components has been discussed and analyzed. Dual wide band-pass FSSs has been designed and developed by using two metallic layers for the wide targeted pass band frequency bands range of 3.53-5.3 GHz and 3.53-4.21 GHz. In the initial step of Development ultra thin double layer slotted FSS has been used. These generate resonance at 4.0 GHz and 4.8 GHz. Furthermore Hilbert shaped slotted resonator increase pass band width enhancement. Lastly the opposite alignment of similar FSS metallic plate to form the proposed dual layer FSS which exhibit the bandwidth enhancement of the frequency bands.

Thicknesses of window glasses, radomes, plastic cases of wireless systems are comparable with the wavelength in the millimeter-wave band. The reflections from the dielectric plate surfaces are canceled out of phase when the thickness is identical to a half of the wavelength. However, they are not canceled at any other frequencies except integer multiple of a half wavelength. Therefore, return loss is a serious problem in the millimeter-wave band. A frequency selective surface (FSS) loaded to the dielectric plate controls reflection amplitude and phase, thus, return loss is canceled for various dielectric thickness and frequency. A complex scattering matrix (S-matrix) of FSS is represented by only reflection amplitude |S 11 | from the condition of zero thickness of FSS expressed by shunt suceptance. The total reflection is calculated by converting S-matrices of FSS and a dielectric plate to a transfer matrices (T-matrix) and synthesizing them. We propose to find the required characteristics of FSS from the desired characteristic of whole structure. Broadband characteristic was designed by inserting FSS at the center of the dielectric plate.

Frequency Selective Surface (FSS) is a specialized structure used in the field of electromagnetic waves and radio frequency (RF) engineering. It is designed to exhibit selective transmission or reflection properties based on the frequency of the incident electromagnetic waves. This article describes the design, construction, and analysis of a textile-based band-stop frequency selective surface for use in the highly EM-polluted GSM, Wi-Fi, LTE, and WiMAX bands. A full-wave EM solver called CST Microwave Studio was used to develop and simulate the unit cell of the proposed FSS at the relevant frequency. In this study, embroidered and screen-printed textile based FSSs were designed. According to the results of this study, it was demonstrated that both embroidery and screen printing FSSs exhibit resonance at a frequency of 3.5 GHz. The screen printing method yielded the best results in terms of resonance frequency sensitivity, while the embroidery method showed a resonance frequency shift. It was observed that the stitch directions and density are important parameters in the embroidery method. Gaps between the embroidery paths in the production of embroidered FSSs resulted in differences from simulations due to the disruption of the structural integrity of the unit cell. Consequently, textile-based FSSs offer advantages over traditional FSSs. This study highlights the potential of textile FSSs as an effective means of reducing electromagnetic pollution, and suggests that further improvements in the design and production processes of textile FSSs can be made.

In this paper, the Minkowski fractal is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not eliminate angular and polarization stabilities. The dimensions of the unit cell are 5 mm × 5 mm and miniaturized 0.095λ0×0.095λ0. The resonance frequency is specified as 5.75 GHz with 155 MHz bandwidth. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

The requirements of frequency-selective surface (FSS) between high transparency in pass band and high reflectance in stop band are contradictory, when they have loaded medium on one side and receive a large range of illumination. In order to solve the contradiction, this paper employs a discrete particle swarm optimization approach (hereafter referred to as a DPSO). In order to seek a balanced FSS with high transparency in pass band and high reflectance in stop band, the periodic intervals and geometrical dimensions of FSS-structures are optimized and designed by using the DPSO method. Simulation and test results indicate that the FSS of super dense Y loop elements in a half-loaded medium structure is presented in this paper: the transparency in pass band and stop band are 80% and 30% respectively. The DPSO method will offer an excellent FSS for the radome which receives a large range of illumination, and on the other hand, it provides a theoretical guidance for the requirements of FSS between high transparency in pass band and high reflectance in stop band.

A methodology is presented for the design synthesis of metamaterials that act as thin multifrequency artificial magnetic conductors. These structures are realized by placing a frequency‐selective surface above a conventional prefect electric conductor, separated by a thin dielectric layer. The frequency‐selective surface design is optimized using a micro‐genetic algorithm to operate at multiple, narrow frequency bands. Two examples of genetically engineered multiband high‐impedance frequency‐selective surfaces (that is, artificial magnetic conductors) are presented and discussed. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 400–403, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11073

The uniplanar compact, affordable, and unique slot‐based multiband frequency selective surface (FSS) of periodic cell size 0.14λc × 0.14λc (λc is wavelength at the initial stopband resonance) is presented in this article. The quadband FSS is analyzed using full‐wave simulation, circuit simulation (ECM), and experimental measurement where good agreement is attained. The FSS offers polarization independence with steady responses for all angular variations in the TE plane and up to 45° in the TM plane. The FSS offers dual stopbands at 2.75–4.15 and 9.45–12.48 GHz and dual passbands at 0.001–0.8 and 4.74–5.6 GHz that includes spectrum coverage of GSM, LTE, WLAN, ISM, WiMAX, and most part of X‐band communication.

Purpose The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were implemented with the ECM and compared with those obtained via Ansys – high frequency structure simulator commercial software simulations. Originality/value The lack of a model of dielectric effective permittivity for the ECM causes a restricted search space in the stochastic FSS design process limited to only geometric parameters, as it is reported in the available literature. The proposed approach simplifies and makes more flexible the design process, and allows guiding the FSS design to unit cell surface and/or dielectric thickness of small dimensions.

A novel method of designing the frequency selective surface (FSS) based on spoof surface plasmon polariton (SSPP) modes is proposed and demonstrated. The high-efficiency transmission and a stopband with a steep falling edge can be mediated by the SSPP modes below and above the cutoff frequency, respectively. So the prolific filtering performances can be customized by integrating with the traditional FSSs. As examples, the two kinds of FSSs were designed and demonstrated by simulations and experiments. A bandstop FSS with the suppression level more than 28 dB is first realized in the frequency region of 9.0–14.7 GHz with the steep rising and falling edges. Then, a dual bandpass FSS is designed by sandwiching the SSPP structure array between the two layers of traditional FSSs. It is indicated that the designed FSS shows two passbands in the frequency ranges of 4.2–4.3 GHz and 8.7–10.3 GHz, and the insert loss is less than 0.5 dB.