Tri-band Frequency Selective Surface Research Articles

Design and analysis of a complementary structure-based high selectivity tri-band frequency selective surface

This work presents a novel tri-band bandpass frequency selective surface (FSS) that achieves high-order filtering responses in different frequency bands by means of a complementary structure. The proposed FSS is composed of three metal periodic arrays, which are separated by multilayer dielectric substrates. The gridded-double convoluted loop (G-DCL) structure, which is the middle layer structure, is a hybrid resonator that generates different resonant frequencies. The top and bottom layer structures are designed as complementary structures to the middle layer. To accurately describe the frequency responses, an equivalent circuit model (ECM) has been constructed over the entire band from 0 to 16 GHz. The results of the simulation indicate that the developed FSS can generate three pass-bands operating at 3.79 GHz, 8.34 GHz, and 12.52 GHz, respectively, and − 3 dB fractional bandwidths are 52.8%, 13.7%, and 19.7%. The transmission responses at the edges of each passband show a quick roll-off from the passband to the stopband, and there is significant out-of-band suppression between adjacent passbands. Moreover, the FSS maintains excellent angular and polarization stability within a 50° range. For verification, the tri-band FSS has been fabricated and tested. The experimental results match the simulation results, validating the accuracy of the FSS design.

Polarization-Insensitive Triband FSS for RF Shielding at Normal and Higher Temperatures by Retrofitting on Ordinary Glass Windows

A comprehensive novel framework for retrofitting frequency-selective surface (FSS) shields to any glass surface using low-cost copper foils has been proposed in this work. The realization technique is demonstrated through a novel triband FSS shield. Global System for Mobile Communication (GSM)-1800, Wi-Fi 2.5 GHz, and wireless local area network (WLAN) 5.6 GHz spectrum, with–10 dB bandwidth of 680, 190, and 1300 MHz, respectively, are suppressed by the shield. The unit cell is made up of a combination of square and circular concentric loops with some alterations. The design is entirely polarization-insensitive and has a steady frequency response for oblique angles up to 60°. The unit element is highly miniaturized for triband operation measuring <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> /9 at 1.8 GHz frequency. An equivalent circuit model (ECM) is also derived to better elaborate the working mechanism of the shield. The pattern is chemically etched on low-cost copper adhesive foil and affixed to ordinary glass as a sticker. The design retains the visual transparency of 72% allowing enough light to enter through windows while rejecting the intended frequencies by at least 28 dB or more in all three bands. The design exhibits a very high shielding efficiency of above 98% for all three bands. Experimental demonstration for single-layer glass, sandwiched glass, as well as air-filled double-glazed glass is carried out. The thermal stability of the proposed design is measured and found intact up to the ambient temperature of 50 °C.

Conformal Miniaturized Angular Stable Triband Frequency Selective Surface for EMI Shielding

This article presents single-layer conformal high angle stable miniaturized triband bandstop frequency selective surface (FSS) for microwave shielding. This new FSS is supported on an ultrathin dielectric substrate and has stable response with change in polarization and incidence angle. Via-less convoluted geometry is adopted in the unit cell design to increase spatial efficiency with a unit cell size of 0.091 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> , where <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> is the wavelength at lowest resonance. The proposed FSS exhibits three transmission zeros at 4, 6.95, 11.3 GHz with stopband bandwidth (BW) founds application for shielding the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> band frequencies for satellite communication. A prototype of the proposed FSS is fabricated. The filter response is measured on normal and on curved surfaces. Simulated and measured transmission coefficients confirm the operating principle of the FSS. Unit cell periodicity of the triband FSS is further reduced by using two layers based 2.5-D geometry. The modified unit cell has a periodicity of 0.038 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> and exhibits stopband BWs center at 0.8, 1.4, and 2.36 GHz.

Design and fabrication of miniaturized tri-band frequency selective surface with polarization-independent and angularly stable response

Abstract A single-layer miniaturized tri-band frequency selective surface (FSS) for bandstop filtering applications has been proposed in this work. The metallic layer with four-branched meandered pattern connected in the center is engraved on a dielectric FR-4 substrate. The three stopbands operating at 2.6, 5.6, and 7.1 GHz provides −10 dB bandwidth of 437, 447, and 552 MHz respectively. The size of the unit cell is 0.067 λ∘ × 0.067 λ∘, where λ∘ is the wavelength of the first resonance frequency. As a figure of merit, the symmetric FSS structure provides the advantage of polarization independence. The proposed compact FSS structure exhibits a stable angular response up to 60° in TE and TM mode. Moreover, measurements obtained from the fabricated prototype are compared with the simulated results and are found to be in close agreement.

A tri-band Frequency-Selective Surface

A novel low-profile tri-band bandpass frequency-selective surface (FSS) is proposed in this paper. The structure is designed by the two-dimensional repetition of a unit cell consisting of four apertures. Each aperture is a combination of T-shaped, U-shaped and a rectangular-shaped aperture aligned horizontally or vertically. The performance of the designed FSS structure is independent of the angle of incidence of the incident wave due to the orientation of the apertures in the unit cell. The designed FSS structure operates at the desired frequency bands close to 8-14 GHz. The insertion loss is close to 3.26, 2.68 and 1.12 dB at the respective frequencies of 8.1, 9.8 and 11 GHz. The advantage of this design is that it exhibits tri-band characteristics for various angles of incidence of the incident wave even though it is a low-profile single layer structure. The total dimensions of the unit cell are approximately 0.55 λ0 × 0.55 λ0 at 8 GHz.

A Tri-band Second-order Frequency Selective Surface Designing and Analysis

In this paper, inspired from the technique of patch–aperture–patch, a novel tri-band frequency selective surface with second-order band-pass response in each operation band is presented. The design is implemented by cascading a two-dimensional periodic array of three square loops and an array of wire grids. The proposed structure composed of three metal and two dielectric layers acts as a spatial dual band microwave filter with large band separation. The predicted FSS has the merits of broadband response, excellent stability for different incident angles, and sharp roll-off at X-, Ku- and K-band, respectively. The simulation and measurement are carried out and discussed. The measured results agree well with the simulated ones.

Independently Tunable Closely Spaced Triband Frequency Selective Surface Unit Cell Using the Third Resonant Mode of Split Ring Slots

In this paper, a tunable triband frequency selective surface unit cell based on varactor-loaded split ring slots is presented. By using the third resonant mode, a considerable mutual coupling reduction between adjacent ring slots is obtained ensuring both close band response as well as independent band tuning. Simulated results show the tunable properties of the proposed approach by shifting the three passbands resonant frequencies from 8.368, 10.276, and 12.010 GHz (for the unloaded split ring slots), to 7.732, 9.202, and 10.900 GHz, respectively, when each split ring slot is loaded with a capacitance of 140 fF. Furthermore, the metal shorts that split the ring slots as well as the metal rings located in between the slots are used to build the conducting paths to bias each varactor with minimum disruption in the RF response. A demonstrator based on an X-band diaphragm was designed, fabricated, and experimentally tested. Measured results using a varactor with capacitance range of 30-65 fF show resonant frequencies for the unbiased varactors at 8.53, 9.70 and 11.47 GHz with insertion loss of 1.1, 2.3 and 2.4 dB, respectively, while biasing the diodes at maximum reverse voltages (24 V) provides resonant frequencies at 8.74, 10.03 and 11.77 GHz with insertion loss of 0.8, 1.4 and 1.7 dB, respectively. Frequency shifts of 210, 330 and 300 MHz for the first, second and third resonant frequencies were obtained, respectively. The -10 dB reflection coefficient bandwidths were 495 MHz for the first band, 436 MHz for the second band and 418 MHz for the third band. Close band response is verified obtaining frequency band ratios of 1.18 and 1.14 for the third to the second resonance, and for the second to the first resonance, respectively.

A Novel Tri-band Frequency Selective Surface

This paper presents a novel tri-band frequency miniaturized frequency selection surface (FSS). The proposed FSS consists of single-node folding and single-node folding bending. The single-layer FSS exhibits three stop bands centered at 2.45, 3.61 and 5.79 GHz, with bandwidths of 0.42, 0.48 and 0.70 GHz, respectively. The proposed FSS has better miniaturization characteristics, and its cell size is 0.126 λ×0.126 λ. The three stop band frequencies of the FSS can be independently controlled by simply changing the length of the corresponding branch. In addition, the proposed FSS is symmetrical about the center and exhibits good resonance stability in both TE and TM polarization. The prototype of the proposed FSS was fabricated and tested, compared with the simulation results, the FSS showed stable performance. This method provides ideas for designing multiband FSS in the future.

A Hybrid Element Triband Frequency Selective Surface With High Angular Stability and Polarization Insensitivity

In this article, a triband frequency selective surface (TBFSS) with narrow band separation is proposed. Pass band frequencies of this TBFSS are 6.9, 8.63 and 10.3 GHz with fractional band width (FBW) of $\text{15.8}\%$ , $\text{13.5}\%$ , and $\text{10.9}\%$ , respectively. Low insertion losses of 0.5, 0.2, and 0.4 dB are observed in the pass bands. These resonant frequencies are adjusted in C and X bands. The unit cell (UC) dimension is $0.2\lambda _0\times 0.2\lambda _0$ which is calculated at lowest transmission zero. Hybrid structural elements are etched on two sides of Rogers 4003 C substrate with $\varepsilon _r$ of 3.38 and thickness of substrate is selected to be 0.406 mm. This design is highly obliquely stable upto $\text{75}^\circ$ . It also shows polarization insensitivity to transverse electric (TE) and transverse magnetic (TM) modes of the plane wave. An equivalent circuit is presented for better understanding of the structure and tuning purpose. A prototype is fabricated to measure the frequency response of the TBFSS. Measured and simulated scattering parameter S $_{21}$ exhibit very good match.

A 20/30 GHz Reflectarray Backed by FSS for Shared Aperture Ku/Ka-Band Satellite Communication Antennas

This letter presents a dual-polarized and dual-frequency reflectarray backed by a frequency selective surface (FSS) with application to shared aperture Ku / Ka -band satellite communication antennas. The reflectarray has been designed to operate simultaneously at 20 and 30 GHz (downlink and uplink frequencies in Ka -band) using a single-layer configuration, where the printed elements are etched on the upper substrate of a two-layer triband FSS. The FSS has been designed to be transmissive at 12 GHz (downlink frequency in Ku -band) and reflective at 20 and 30 GHz. An 18 × 18-cm2 prototype has been fabricated and tested, showing a good matching with the simulations. The measured gains are 28.5 dBi at 20 GHz and 32.25 dBi at 30 GHz.

Design and analysis of a tri-band frequency selective surface with a second-order response

AbstractIn this paper, a sandwiched type frequency selective surface (FSS) is designed and analyzed. The design procedure and operating principle is given based on the equivalent circuit model. The proposed FSS includes two identical layers of periodic metallic arrays, which are separated by a foam layer. In each layer of the periodic array, the unit cell is composed of a gridded-triple square loop structure. The FSS provides three pass-bands, in which a flat band response is presented. Three bands are separated by one or two transmission zeros, which leads to a sharp rejection on both sides of each pass-band. The central frequencies of the three pass-bands are 7.0, 10.9 and 14.0 GHz. To verify the simulated results, a prototype of the FSS is fabricated and measured. The simulated results agree well with the measured ones. This work can be used in area of a radar stealth or satellite communication system.

An FSS Structure Based on Parallel &lt;italic&gt;LC&lt;/italic&gt; Resonators for Multiband Applications

An frequency selective surface (FSS) structure based on parallel LC resonators is proposed to achieve multiband bandpass filtering responses. The parallel LC resonator, implemented by a via-connected metallic line and a parallel-plate capacitor (PPC), serves as the basic element for intentionally constructing FSS unit cell, which exhibits a single-band bandpass filtering response. As a result, the proposed FSS structure can provide a multiband performance by introducing multiple VCMLs and PPCs with different resonance frequencies. Because of the compact resonator resulting from a PPC, the proposed FSSs feature miniaturized unit cell size inherently, for example, the single-band FSS element is as compact as 4.8% of the operating wavelength. Moreover, this kind of FSS structure is also beneficial for independent control of the frequency performance under different polarizations, efficient optimal design of desired resonance frequencies, and easy realization of multiband response with wideband ratio range (e.g., 1.13 to 3.32 for the dual-band FSS). Equivalent circuits of these FSSs are established for explaining the resonating mechanisms and precisely modeling the frequency performances. Finally, prototypes of the dual- and tri-band FSSs are fabricated and measured. The measured results exhibit stable filtering performance under different polarizations and incidence angles (up to 60°).

A Miniaturized Triband Frequency Selective Surface Based on Convoluted Design

A novel miniaturized tri-band frequency selective surface (FSS) based on convoluted design has been proposed in this letter. The proposed FSS is a low-profile structure, and it is composed of two periodic metallic arrays separated by a thin dielectric substrate. The top metallic array is composed of four branched spiral triangles connected in the center, and the bottom one is consisting of gridded tortuous cross-dipole. The proposed FSS can provide three passbands operating at 3.28, 4.2, and 5.4 GHz, respectively. The unit cell is only 0.066 λ 0 × 0.066 λ 0 in size, where λ 0 is the wavelength of the first resonant frequency in free space. In addition, the proposed FSS provides a stable performance under oblique incidence for both TE and TM polarizations. For verification, an FSS prototype has been fabricated and measured. Good agreements between the simulated and the measured results can be observed.

A Tri-Band Frequency Selective Surface (FSS) to Diplex Widely Separated Bands for Millimeter Wave Remote Sensing

A substrate-backed frequency selective surface (FSS) is presented for diplexing the widely separated frequency spectrum centered at 55, 89, and 183 GHz with varying bandwidth for spatial separation in the quasi-optical feed network of the millimeter wave sounder. A unit cell composed of a crossed dipole integrated with a circular ring and loaded inside a square ring is optimized for tri-band frequency response with transmission window at 89 GHz and rejection windows at 55 and 183 GHz. The reflection and transmission losses predicted for the optimized unit cell (728 μm × 728 μm) composed of dissimilar resonant shapes is less than 0.5 dB for transverse electric (TE) and transverse magnetic (TM) polarizations and wide angle of incidence (0°–45°). The FSS is fabricated on a 175-μm-thick quartz substrate using microfabrication techniques. The transmission characteristics measured with continuous wave (CW) terahertz transmit receive system are in good agreement with the numerical simulations.

Closely spaced tri‐band frequency selective surfaces based on split ring slots

A tri-band frequency selective surface (FSS) with close band spacing based on split ring slots for y-polarised incident waves is investigated. The close band response is obtained by reducing the strong mutual coupling between the closely packed concentric rings through splitting the ring slots and redistributing the location of the surface currents at resonances. To validate the proposed FSS, a Ka band FSS was designed, fabricated and tested. Experimental results showed closely spaced resonances at 27.3, 31.7 and 36.2 GHz. Frequency ratios of 1.16 for the second to the first resonance, and 1.14 for the third to the second one were obtained. Also, good stability is observed for oblique incidence.

Multi‐layer tri‐band frequency selective surface using stepped‐ and uniform‐impedance resonators

A novel tri-band frequency selective surface (FSS) is proposed by using multi-layer printed circuit boards with a number of via holes. Three separate propagation paths with two stepped-impedance resonators (SIRs) and a uniform-impedance resonator (UIR) are constructed in each unit cell of the proposed FSS, thus leading to tri-band bandpass performance. The lowest and the middle frequency bands are achieved by two SIRs, respectively, and the highest frequency band is obtained by the resonance of the UIR. Therefore, these three passbands can be realised independently, which can increase the design freedom. The operating principle is explained by analysing the electric field distributions. To verify the design concept, a prototype of the proposed FSS is simulated and tested. Measured results show that the FSS features stable tri-band performance under a large variation of incident angle.

Triband Frequency-Selective Surface as Subreflector in Ku-, K-, and Ka-Bands

A novel triband frequency-selective surface (FSS) is designed to be a subreflector for reflector antennas. The element of the proposed FSS structure consists mainly of two identical layers of a square loop combined with a hexagonal ring and a hexagon. The designed FSS reflects electromagnetic waves in Ku-band (12–15.2 GHz), but transmits electromagnetic waves in K-band (18–21.6 GHz) and Ka-band (29.3–32 GHz). Moreover, such an FSS has the merit of stable performance for various incident angles within 50° for both TE and TM polarizations. Simulated results show that the insertion losses in K-band are less than 0.5 dB when the incident angles vary from 0° to 45°, and less than 1 dB for the incident angles from 45° to 50°. In Ka-band, the insertion losses are less than 0.5 dB when the incident angles vary from 0° to 30°, and less than 1 dB when the incident angles are from 30° to 50°. For both TE and TM polarizations, the incident angle is up to 50° with S 21 less than −15 dB in Ku-band. Both designed procedure and measured results of the FSS are presented and discussed.

Planar tri-band frequency selective surface with transmission in S-band and reflection in Ka/Ku-band

In this paper a novel low-profile single-layer tri-band frequency selective surface (FSS) unit-cell, which consists of dual concentric modified circular ring, is analyzed and simulated. It can be utilized in the satellite communication systems and electromagnetic shielding applications. The proposed structure has been developed using the modifications in the concentric circular rings FSS in order to obtain the significant percentage of fractional bandwidth and stable frequency response for the perpendicular (TE) and parallel (TM) polarized waves for incidence angles up to 50°. We have also compared the polarization and angular stability performance of the proposed FSS structure with that of the another reported in the literature.

A Triband Second-Order Frequency Selective Surface

In this letter, we propose a triband second-order fre-quency selective surface (FSS). Each second-order bandpass re-sponse is realized by a three-layer patch-aperture-patch (PAP) structure. The PAP elements with different sizes are then arranged to a unit cell that is to be repeated periodically. Based on this tech- nique, an FSS unit cell with triband second-order response is de- signed. There is a respective second-order bandpass response for each operation band. The triband FSS has the merits of high selec-tivity and stable performance for incident angles within 30° and for different polarizations.

Triband Frequency Selective Surface With Periodic Cell Perturbation

A novel triband frequency selective surface (FSS) constructed by square loop slots etched on substrate integrated waveguide cavities (SLS-SIWC) is investigated, in which each periodic cell consists of two neighboring SLS-SIWCs with different dimensions. Good selectivity performance of each passband can be easily achieved by tuning the dimensions of the SLS-SIWCs. Besides, the passbands are mainly determined by the corresponding SLS-SIWC in the neighboring perturbed cells and can be designed independently. The performance is verified by measured results, which is insensitive to the variation of incident angles. According to the explicit physical concept, some improved analytical formulas are adopted, which makes the design process straightforward and simple