Prototype Of Frequency Selective Surface Research Articles

An ultra‐miniaturized single‐layer multiband frequency selective surface with vent for wireless communication

SummaryA novel single‐layer ultra‐miniaturized multi‐band Frequency Selective Surface (FSS) with a circular vent is designed for shielding LTE and ISM bands. The top layer of the proposed FSS unit cell incorporates a circular patch along with convoluted arms. The designed FSS unit cell exhibits band‐rejection characteristics with a resonance of 800 MHz, 2.45 GHz, and 5 GHz and bandwidths of 523 MHz, 687 MHz, and 725 MHz, respectively. The periodicity of an ultra‐miniaturized FSS unit cell is 0.024λօ x 0.024λօ, encompassing a spatial vent hole of 0.01λօ, where λօ corresponds to the lowest operating frequency. Moreover, the proposed FSS unit cell remains unaltered angular stability up to 75° with less than 1% frequency deviation in TE and TM modes. Good polarization insensitivity for the designed four‐fold symmetrical FSS unit cell is achieved. Further, an Equivalent Circuit Model (ECM) analysis is developed to infer the physical insight of the proposed FSS unit cell. The FSS prototype is measured for the assertion, and the good agreement between the findings from simulation and measurement is validated. For real‐time assertion, the FSS prototype is verified using the Amitech SDR04. Thus, FSS is a promising candidate with good ventilation for shielding the LTE, Bluetooth, and Wi‐Fi application bands.

A Dual-Band Polarization-Insensitive Frequency Selective Surface for Electromagnetic Shielding Applications.

This paper presents a novel polarization-insensitive dual-band frequency-selective surface (FSS)-based electromagnetic shield. The miniaturized FSS unit cell consists of a modified Jerusalem crossed loop and a corner-modified square loop. These FSS elements are arranged in a co-planner configuration over a single-layer Rogers 5880 substrate and simultaneously offer effective shielding in the X- and Ku-bands. Moreover, the FSS manifests polarization-independent and angularly stable band-reject filter characteristics over various oblique angles of incidence for both the TE and TM polarizations with virtuous attenuation at both resonances. In addition, the FSS structure is modelled into an equivalent lumped circuit to better analyze the phenomenon of EM wave suppression. A finite prototype of FSS is fabricated and tested. The simulated and measured results are in good agreement, thus making it a potential candidate for RF shielding/isolation applications.

A Novel Ultra-Miniaturized Angularly Stable Frequency Selective Surface for L-Band Shielding Applications

This paper presents a novel ultraminiaturized frequency selective surface (FSS) for L-band electromagnetic shielding applications. A basic square loop incorporated with folded arms in the top layer constructs the single-layer FSS design. Band-stop characteristics for the entire L-band operating frequency ranging from 1 GHz to 2 GHz are offered by the proposed design. An ultraminiaturized profile of 0.028λο × 0.028λο is achieved by the designed FSS, where λο corresponds to the lowest operating frequency, achieving at least 32.1% miniaturization when compared to the state-of-the-art FSS designs in the literature. Polarization insensitivity with a peak shielding effectiveness of 45.4 dB is manifested by the rotational symmetry of the proposed design. The proposed FSS exhibits excellent angular stability performance up to 80° with a frequency deviation of less than 1%. The equivalent circuit model helps to understand the working principle of the proposed FSS. The experimental results of the designed FSS prototype agree well with the simulation results. Hence, the proposed spatial filter is a suitable candidate for enhancing security in wireless communication at the carrier frequencies of GPS systems.

A Quad-Band Highly Selective Frequency Selective Surface with Ultra-Wideband Rejection.

In this paper, a highly selective quad-band frequency selective surface (FSS) with ultra-wideband rejection is presented. The proposed FSS structure was developed by cascading five metallic layers by three thin dielectric substrates. The five metallic layers are composed of two bent slot layers, two metallic square rings, and a metal patch. The dimensions of the unit cell are 0.13λ0× 0.13λ0× 0.18λ0 (λ0 is the free-space wavelength at the first operating frequency). The proposed structure achieves four transmission bands and has two wide stop-bands located at 1 to 5.5 GHz and 14 to 40 GHz, with a suppressed transmission coefficient below -20 dB. In order to verify the simulation results, an FSS prototype was fabricated and measured. It can be observed that the measured results are in favorable agreement with the simulation results. Its multiple narrow passbands and highly selective and ultra-wideband rejection properties ensure that our design can play a significant role in narrowband antennas, spatial filters, and many other fields.

High Selectivity FSS With Three Independently Controllable Transmission Poles Using Matrix Synthesis

In this letter, a high selectivity frequency selective surface (FSS) with three independently controllable transmission poles (TPs) is proposed by using matrix synthesis. The response with three TPs and four transmission zeros is obtained by employing a triplet topology. The matrix synthesis method provides a theoretical analysis for coupling elements regarding to three independently controllable TPs. Also, the synthesized matrix gives a good prediction of flexile responses with allocated center frequency and bandwidth. To be verified, a finite FSS prototype with 15 × 15 unit cells is fabricated and tested. The measured results are mostly consistent with simulated and synthesized ones, manifesting merits of high selectivity, flexible design, and low profile.

Design and demonstration of a 2.5D frequency‐selective surface for sub‐6 GHz 5G wireless communication

AbstractThis paper presents an ultraminiaturized bandstop closed‐loop 2.5D frequency‐selective surface (FSS) for sub‐6 GHz 5G wireless communication. Four metallic vertical vias interconnect metallic elements present on both sides of the substrate to form a modified closed‐loop design. The proposed structure band stops the entire sub‐6 GHz 5G band (C‐band/NR N78 band/LTE 42/43 band) ranging from 3.2 to 3.9 GHz with a resonant notch at 3.62 GHz. This design supports polarization insensitivity and procures maximum relative deviation of 0.5% and 0.2% at 80°incident transverse electric (TE) and transverse magnetic (TM) polarized waves, respectively. The proposed FSS prototype has been fabricated and tested. Experimentally, the resonant notch is obtained at 3.55 and 3.68 GHz under TE and TM normal incident polarized waves, respectively. Moreover, good agreement in the frequency response curves is observed between simulated and measured results. The proposed unit cell is 3.6 × 3.6 mm2 in dimensions, which is 0.04λ × 0.04λ, where λ is the resonant wavelength.

Synthesis Design of Bandpass Frequency Selective Surface With Multiple Transmission Zeros Using Slotline Structures

This article presents a synthesis method to design a new type of bandpass frequency selective surfaces (FSSs) with multiple transmission zeros (TZs). To briefly show the concept of our synthesis method, a generalized topology of the bandpass FSS based on cascaded slotline sections paralleled with bandpass resonators is first presented to map with an alternative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> th-order bandpass filtering network with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$J$ </tex-math></inline-formula> -inverters and typical LC parallel resonators. Then, two kinds of composite LC parallel resonators, named as LC – LC and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula> – LC parallel resonators, are introduced and discussed to replace the typical LC parallel resonators, which can produce TZs at skirts of the passband and increase the out-of-band selectivity. The derivations of equivalent relationships between the composite and typical LC resonators are given. Furthermore, for the exploration of bandpass FSS with multiple out-of-band TZs, the realization of these two discussed composite LC parallel resonators is exhibited by inductive and capacitive strip lines loading on slotline structures. The design curves and guidelines are given and discussed correspondingly. To validate our design concept, two FSS examples, a second-order bandpass FSS with four out-of-band TZs and a third-order one with five out-of-band TZs, are synthesized and designed. In final, these two designed bandpass FSS prototypes are fabricated and then measured by the free-space measurement method. The measured results show that the desired stable bandpass filtering performance and independently multiple out-of-band TZs are successfully realized.

A design of broadband bandpass frequency selective surface

AbstractIn this paper, a broadband frequency selective surface (FSS) based on a multilayer coupling cascade is presented. The overall structure consists of three metallic layers and two dielectric substrates. In addition, a crosspatch terminated with an E‐shaped structure and a gradient cross structure with a slot is introduced in the middle metallic layer to control the transmission zero and extent of the current path, respectively. The unit cell periodicity is about 0.27 , and the overall thickness of the dielectric layer is about 0.087 . Prototypes of the proposed FSS are designed and simulated, and an equivalent circuit model is developed to explain the mechanism further. Finally, the FSS prototype works at the center frequency of 12.2 GHz with a relative −0.5 dB bandwidth of 70% and a relative −3dB bandwidth of 104%. The frequency responses are relatively stable with the variation of incidence angles from 0° to 60°.

Miniaturized Frequency Selective Surface for 6G Communication.

A single-layer, quartz-supported frequency selective surface (FSS) with a gear-shaped metallic array is proposed for 6G communication. Full-wave simulation, along with the method of equivalent circuit, is applied to investigate the transmission characteristics, while the distributions of surface current distribution, as well as electric field and magnetic fields, are studied to further interpret the transmission mechanism. The simulation indicates that the resonant frequency of 131 GHz with an attenuation of −40 dB can be obtained and the relative bandwidth approximates to 12%. The transmission response of the fabricated FSS prototype is measured using the free space measurement setup. The measured results show a good agreement with the simulated ones, which demonstrates the reliability of the design and fabrication. The proposed FSS with the advantages of simple structure, low cost, easy fabrication, and integration can be applied in enhancing the communication performance and anti-interference ability in the future 6G communication system.

Ultrathin narrowband frequency selective surface with high angular and polarization stability at X‐band frequencies

AbstractAn experimental investigation of an ultrathin and narrowband frequency selective surface (FSS) with polarization‐insensitive and high angular stability at X‐band is reported. A roll‐off and narrow‐passband behavior of the FSS spatial filter is designed by coupling two layers of periodic square slot loops of resonance, which are etched on the top and bottom metal surfaces of a two‐substrate‐stacked printed circuit board (PCB). The sandwiched interface between these two PCB substrates is also a metal surface with periodic square slots for proper coupling. The bandpass nature is numerically simulated by high‐frequency structure simulator and is further validated by experimental measurements on an FSS prototype. The prototype comprises 50 × 33 unit cells in an area of 40 cm × 26.4 cm, and the total thickness is 0.025 λ. The experimental results show a resonant frequency at 12.23 GHz with a 3 dB relative bandwidth of 6.1%. The maximum frequency deviation of bandwidth is less than 0.4% for the incident angles from 0° to 60°, exhibiting good frequency stability.

A Miniaturized Quad-Stopband Frequency Selective Surface with Convoluted and Interdigitated Stripe Based on Equivalent Circuit Model Analysis.

This paper presents a miniaturized frequency selective surface (FSS) based on the convoluted and interdigitated stripe with multiple narrow passbands/wide stopbands in the L-/S-/C-/X-/Ku-/K-band. By using the convoluted and interdigitated stripe, the coupling inside is well controlled, so that the spatial efficiency is maximized to provide a high miniaturization. An equivalent circuit model is presented to reveal the working mechanism of the proposed FSS. The proposed structure forms four transmission band rejections of 3 dB in 1–6.65 GHz, 8.35–16.9 GHz, 18.0–24 GHz, and 24.50–27.84 GHz. The size of the unit cell is 0.09λ0 × 0.09λ0, where λ0 is the wavelength of the first resonance frequency. The proposed FSS has a good angle stability and polarization stability in a scanning range up to 60°. For verification, an FSS prototype has been fabricated and measured. The measured results were in agreement with the simulated results. The proposed FSS can be used in practical applications such as radomes, antenna reflectors, and spatial filters.

Compact Dual-Passband Three-Dimensional FSS with Good Angular Stability and Both-Side Fast Roll-Off Characteristics

A compact dual-passband three-dimensional (3D) frequency selective surface (FSS) is proposed based on multiple square coaxial waveguides (SCWs), which exhibits good angular stability and both-side fast roll-off characteristics. The unit cell of the proposed 3D FSS is composed of one parallel plate waveguide (PPW) propagation path and two SCW propagation paths. By etching a centered annular slot, each SCW path forms two identical short SCWs. Each short SCW inherently generates one square slot resonance. In each SCW path, on the account of electromagnetic coupling between two square slot resonators provided by two short SCWs, the square slot resonant mode will split into even-/odd-resonant modes. Accordingly, each SCW path can provide a flat second-order passband with two transmission poles. Due to the reflection and out of phase of electromagnetic waves, four transmission zeros located at both sides of the passbands are introduced for high frequency selectivity, realizing both-side fast roll-off performances. In order to explain the operating principle, the electric-field distributions at transmission-zero/pole frequencies are investigated. Finally, an FSS prototype is fabricated and measured, and the results exhibit good angular stability for both TE and TM polarizations under incident angles from 0° to 60°. In addition, the proposed 3D FSS has a compact unit cell.

Design of miniaturized FSS using equivalent circuit model and multi-objective particle swarm optimization

A method for designing miniaturized frequency selective surface (FSS) using equivalent circuit model (ECM) and multi-objective particle swarm optimization (MOPSO) algorithm is proposed in this paper. In the proposed method, ECM describing the desired frequency response is established, and parameters of the ECM are determined using the MOPSO algorithm. Combining the ECM analysis and the MOPSO algorithm, the requirements of desired frequency response can be converted into the constraints of equivalent circuit parameters, which simplifies the optimization process of FSS design. For verification, a single-layer bandstop-bandpass FSS composed of convoluted elements with the unit cell size of 0.073λ 0 × 0.073λ 0 is designed. Simulation results show that the −15 dB bandwidth is from 2.62 to 2.83 GHz, and the −0.5 dB bandwidth is from 3.84 to 5 GHz. Meanwhile, the resonant frequency is stable at different incident angles (up to 80°) under TE and TM polarization. Finally, the proposed FSS prototype is fabricated and measured. The measured results agree well with the simulated ones.

Narrow Bandpass Frequency Selective Surface With High Level of Angular Stability at Ka-Band

In this letter, a novel design of a narrow bandpass frequency selective surface (FSS) based on the utilization of the coupled method, which resonates at Ka-band frequencies between 29 and 30.3 GHz, is proposed and experimentally evaluated. A high selectivity was achieved, by coupling two metallic layers, which were based on the structure of a cross aperture and a rectangle grid patch, respectively. The simple symmetric patterns used in the proposed work have also made the FSS independent of polarization properties. Moreover, a high angular stability was also achieved since for electromagnetic (EM) wave incident at degrees from 0° to 75°, the frequency deviations were only 0.1% and 0.4% for TE and TM polarizations, respectively. For performance evaluation, an experimental FSS prototype was fabricated by a double-sided printed circuit board (PCB), which was composed of 50×50 unit cells in a dimension of 18 cm ×18 cm. A Keysight N5227A PNA and two-horn antennas in a chamber were setup to measure the performance. The experimental measurement results have shown a good agreement with the numerical simulations.

Close Band Spacing Pentaband Frequency Selective Surfaces Based on Concentric Ring Slots

This paper presents a polarization insensitive frequency selective surface (FSS) based on concentric ring slots with five closely spaced passbands. The proposed FSS unit cell contains five ring slots coupled with a supplementary innermost ring slot. The close band response within the first five transmission bands is achieved by the influence of the modified geometry obtained with the inclusion of the sixth ring slot. This added ring slot causes the appearance of a stopband, due to the conductive ring between the fifth and the sixth ring apertures, and a passband produced inherently by the sixth ring aperture. The effect of the additional stopband and passband in the FSS response has been investigated in the paper. Full-wave simulations reveal that a modified geometry with proper sizes effectively enables the close band response of the pentaband FSS. To validate the proposed approach, a 729-element penta-bandpass FSS prototype operating at millimeter-wave frequencies has been designed, fabricated, and tested. Experimental results in a free-space measurement setup indicate resonances at $f_{1} =26.7$ , $f_{2} =29.8$ , $f_{3} =33.6$ , $f_{4} =38.1$ , and $f_{5} =44.2$ GHz, with resonant frequency ratios of $f_{2} / f_{1} =1.12$ , $f_{3} / f_{2} =1.13$ , $f_{4} / f_{3} =1.13$ , and $f_{5} / f_{4} =1.16$ . This FSS demonstrates an extremely low ratio of the highest and the lowest resonant frequencies ( $f_{5} / f_{1} =1.66$ ) for a penta-band operation. This polarization insensitive FSS demonstrates good performance at oblique angular incidence for elevation angles up to 45°.

High‐order bandpass frequency selective surface based on aperture‐coupled patch resonators under dual resonance

A bandpass frequency selective surface (FSS) with fourth-order bandpass filtering response is proposed based on aperture-coupled patch resonators (ACPRs) under the operation of TM010 and TM030 resonant modes. An initial bandpass ACPRs FSS with second-order filtering response is firstly realised by periodically arranging the back-to-back patch resonators with coupling apertures etched on the common ground. In order to combine the resonant modes TM010 and TM030 for a higher-order filtering response, seven pairs of shorting pins are properly loaded based on the cavity model theory for the microstrip patch resonator. The loaded shorting pins make the TM010 mode of the ACPRs shift towards the higher frequency, while the TM030 mode keeps nearly unchanged. As a result, these two resonant modes can be allocated in proximity to each other to finally realise a fourth-order bandpass filtering response. To validate the design concept, an FSS prototype is designed and fabricated. Reasonable agreement between the measured and simulated results validates the conceptual design.

An Improved Fabrication Technique for the 3-D Frequency Selective Surface based on Water Transfer Printing Technology

Manufacturing an array of high-quality metallic pattern layers on a dielectric substrate remains a major challenge in the development of flexible and 3-D frequency selective surfaces (FSS). This paper proposes an improved fabrication solution for the 3-D FSS based on water transfer printing (WTP) technology. The main advantages of the proposed solution are its ability to transform complicated 2-D planar FSS patterns into 3-D structures while improving both manufacturing quality and production costs. WTP technology makes use of water surface tension to keep the thin metallic patterns of the proposed FSS floating flat with the absence of a solid planar substrate. This feature enables these metallic FSS patterns to be transferred onto 3-D structures through a dipping process. To test the effectiveness of the proposed technique, the FSS was designed using computer simulation software Microwave Studio to obtain the numerical performance of the FSS structure. The WTP technology was then used to fabricate the proposed FSS prototype before its performance was tested experimentally. The measurement results agreed well with the numerical results, indicating the proposed manufacturing solution would support the development of complicated 3-D electronics devices, such as conformal antenna arrays and metamaterials.

Design and Synthesis of Band-Pass Frequency Selective Surface With Wideband Rejection and Fast Roll-Off Characteristics for Radome Applications

In this article, we proposed an equivalent circuit-based design to synthesizing second-order band-pass frequency selective surfaces (FSSs) with wide out-of-band rejection and fast roll-off characteristics. An equivalent circuit model (ECM) is established in order to depict the desired frequency response. Then, based on the ECM, a generalized composite structure comprised of three FSS arrays separated by two dielectric substrates is proposed. The main advantage of this method is that it allows us to acquire optimized structural parameters according to the desired frequency response. With this method, an FSS based on the proposed composite structure is designed. The designed FSS can provide a second-order pass-band within the stop-band ranging from 1 to 40 GHz and the pass-band is operating at 10 GHz with 12% fractional bandwidth. Meanwhile, the bandwidth of the two transitional bands on both sides of the pass-band is only 0.26 and 0.6 GHz, respectively. Also, the frequency response of the designed FSS is stable at 60° for both TE and TM polarizations. For further verification, an FSS prototype is fabricated and experimentally characterized. Good agreements between the simulated and measured results can be observed.

A New Conductive Ink for Microstrip Antenna and Bioinspired FSS Designs on Glass and Fiberglass Substrates

Abstract This paper describes an investigation of the possibility of using a new conductive ink, insted of copper clad laminates, in the manufacturing of microstrip patch antennas on glass and fiberglass substrates and of bioinspired frequency selective surfaces (FSSs) on fiberglass substrates for wireless communication systems. The new conductive ink is developed using synthesized nitrocellulose which, in ethyl acetate solution, works as a bonding agent and carrier for the formation of a conductive film. The load used in the fabrication process is silver metallic powder. Simulation and analysis are performed using Ansoft Designer and HFSS softwares. Microstrip antenna and FSS prototypes are fabricated and measured for comparison purpose. An agreement is observed between simulation and measurements results.

Graphene-based active frequency selective surface in microwave frequency

Electrical controllable charge density in graphene films has recently attracted considerable research interest for its potential applications in various active devices. In this letter, we demonstrate that graphene acts as an effective tunable loss resource to manipulate the electromagnetic response of a metallic resonant structure at microwave frequency. A transmission-tunable frequency selective surface (FSS) is realized by introducing a graphene sandwich into its near-field region. Remarkable transmission tuning from 81.7% to 25.2% at a resonant frequency of about 6.5 GHz is observed when applying bias voltage from 0 to 3.6 V. The graphene FSS prototype may open up a way for realizing electromagnetic active devices in the microwave range.