Frequency Selective Surface Structure Research Articles

Design and analysis of frequency selective surface embedded broadband high gain miniaturized antenna

SummaryIncorporating the better impedance matching capability of planar curved radiating patch, a miniaturized broadband planar antenna has been designed, analyzed, and integrated with frequency selective surface (FSS) to accomplish higher gain for various short‐range and long‐range modern wireless communication applications. Physical and electrical volume of the presented antenna is 25 × 20 × 1.6 and 0.25 × 0.20 × 0.016, respectively. The proposed radiating patch is constructed from a conventional rectangular patch by transforming the upper side of the patch into a semi‐circular shape and the lower side of the patch into a staircase‐like shape. Measured outcomes of the designed antenna show a very large operating bandwidth of 19.8 GHz (3–22.8 GHz) with a fractional bandwidth (FBW) of 153.5% and bandwidth dimension ratio (BDR) of 3070. An equivalent circuit model (ECM) of the proposed antenna is developed using an advanced design system (ADS) circuit simulator. The frequency responses of the ECM are compared with the simulation done by CST Microwave Studio Suite software and measurement results, which show good agreement. An FSS structure with stop band from 2–28 GHz is positioned beneath the proposed antenna at optimal position (27 mm below the antenna) to enhance the gain up to 8.9 dBi. The presented antenna and FSS are fabricated on FR4 substrate and experimentally verified using standard microwave measurement setup.

Dual-polarized angle-selective surface based on double-layer frequency selective surface

In this Letter, we propose a dual-polarized angle-selective surface (ASS) based on a double-layer frequency selective surface (FSS) to achieve angular selectivity. By appropriately constructing the structure of the single-layer FSS, bandpass and band-stop are produced by the ASS under normal and oblique incidences, respectively, resulting in exceptional angular selectivity. Simulated results show that the proposed low-pass ASS achieves a bandpass (|S21| > −1 dB) from 0° to 10° and a band-stop (|S21| < −20 dB) from 31° to 85° with a profile thickness of 0.6 λ. A low-pass ASS prototype with an operating frequency of 10 GHz is fabricated to demonstrate the design concept. The measured results of the transmission coefficients are in good agreement with the simulated results. The proposed ASS can play an important role in many applications, as in minimizing the side lobes of the antenna.

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.

X-band frequency selective surface with low loss and angular stability

A bandpass frequency selective surface (FSS) with low loss and angular stability based on three metal layers is proposed in this paper. The top and bottom resonant layers are coupled through a metal ring layer to build the FSS structure. The equivalent circuit model is derived to explain the operation principle of the proposed FSS. In the design, two transmission zeros (TZs) are generated at both sides of the passband contributing to the high selectivity performance. Furthermore, current distributions are given to analyze the generation mechanism of the TZs. The performance of the proposed FSS is insensitive to the polarization and angle of the incident wave. To verify the performance, a prototype of the FSS is fabricated, whose measured results agree with the simulated ones. The FSS shows low-profile of about 0.07λ (λ is the free space wavelength at the center frequency).

Bandwidth-enhanced FSS-loaded Semi-circular Patch Antenna for C-band Applications

Aim: This study aimed to develop and analyse a bandwidth-enhanced C band antenna loaded with EBG and FSS Structures to improve the antenna performance. Methods: This paper illustrates the design of a semi-circular microstrip antenna with a modified circular ring Frequency Selective Surface (FSS) and an Electromagnetic Band Gap (EBG) structure for improved bandwidth and an omnidirectional pattern. The patch antenna is aimed at C-Band intersatellite communication links in a constellation. Results and Discussion: In literature, the application of EBG and FSS together is seldom used. The semicircular patch is aimed at retaining the omnidirectional antenna pattern at higher frequencies, as well as bandwidth, which is achieved through FSS and EBG structures. The modeling and simulation of the antenna have been carried out with 3D EM solvers. The simulated patch antenna operates in a wideband ranging from 4.1 GHz to 7.1 GHz with a gain of 1.9 dB at 5.33 GHz and 1.4 dB at 4.5 GHz. Conclusion: The proposed antenna design is vertically polarized. The simulation results are validated with measurement results.

A Proposed Frequency Selective Surface (FSS) using Bio-Inspired Element for Wi-Fi 6E Applications

Recently bio-inspired elements with shapes or geometries found in nature have received special attention, both for applications in antennas and in electromagnetic filters, the unit cell of the proposed FSS consists of a modification in a bio-inspired shaped element. A single and multilayered band-stop Frequency Selective Surface (FSS), with polarization independence, is proposed to be used in frequency applications at 6.0 GHz (Wi-Fi 6E). In the industry, Wi-Fi 6E is the name that identifies those Wi-Fi devices that operate in the 6.0 GHz band, designed to improve efficiency and more capacity than previous standards. Band-stop frequency responses for the single and multilayer structures are presented. The simulated frequency responses show bandwidth values for inhibit transmission about of 1.75 GHz and 3.15 GHz, respectively for single and multilayer structures. Furthermore, good agreement between simulated and measured results is shown for the single bio-inspired FSS. The proposed FSS structure presents features that allow its use as an electromagnetic filter or its integration with microstrip antennas developed for applications in the same standard.

Design of single‐layer bandstop fractal frequency selective surface based on WLAN applications

AbstractIn this letter, we present a new frequency selective surface (FSS) for shielding 2.4–2.5 and 4.98–5.825 GHz wireless local area network (WLAN) bands. This FSS structure is based on the traditional Sierpinski octagon and we improve it. Compared with the traditional structure, the improved one has a smaller element size and better angular stability. The design is realized on float glass with a relative permittivity () of 8, and the unit cell size is 0.1152λ0 × 0.1152λ0 (λ0 is the free space wavelength at the first resonant frequency). Wide rejection bandwidths (−10 dB) of 910 and 1630 MHz are obtained at 2.4–2.5 and 4.98–5.825 GHz, respectively. The surface current distribution and the equivalent circuit model are illustrated to explain the resonance behavior of the proposed FSS. Furthermore, this FSS exhibits stable frequency response to incident angles of 0°–80° under transverse electric and transverse magnetic polarizations. Finally, this FSS structure was fabricated and measured. The measured results demonstrate that this FSS structure has good performance in WLAN applications.

A specialized partial discretized optimization algorithm for SLL suppression in FSS design

Side Lobe Level (SLL) suppression is a challenging but essential part of frequency selective surface (FSS) structural design. The SLL of the radiation pattern is a key parameter demonstrating the directional anti-interference ability and mainly depends on the geometry of the FSS. However, the correlation between SLL and FSS structural parameters is extremely complicated. A minor FSS structure change may result in a drastic diversion in the sidelobe’s direction or level, making the SLL the most difficult parameter to optimize. In this paper, an efficient optimization method specifically for SLL suppression is proposed. We discretized the edges of split square ring FSS structures by binary representation and generated new patterns based on the genetic algorithm. Optimization results showed that in the most optimal structure, the SLL was −23.41 dB, exhibiting a 5.17 dB reduction. Meanwhile, the center frequency variation was less than 2%. Moreover, the computation time cost was reduced by over 90% compared with that of the fully discretized pattern optimization method, showing that this novel method was truly effective in getting SLL suppressed FSS structures.

Design of Miniaturized FSS with High Angular Stability Utilizing a Novel Closed Loop

In this paper, we propose a miniaturized 2.5-dimensional (2.5D) frequency selective surface (FSS) structure with high angular stability. A novel closed-loop FSS is formed by combining the Jerusalem cross (JC) structure with the conventional rectangular closed loop using vias. This approach further enhances the coupling performance of the FSS and thus achieves miniaturized design. The unit cell size of the proposed FSS is 0.019λ0 × 0.019λ0 at the resonant frequency, and the metal is printed on a dielectric substrate with a thickness of 0.003λ0. The proposed FSS has a resonant frequency of 850 MHz and exhibits band-stop characteristics. It is insensitive to the incident angle with a good operating performance in both the TE and TM wave modes. Therefore, it can be well used as an electromagnetic shield for the GSM 850 band. In order to facilitate the rapid analysis and design of the FSS, the equivalent circuit model is further analyzed and established, and values of the corresponding lumped components are derived. In addition, a prototype FSS is fabricated using printed circuit board technology and is tested in a microwave anechoic chamber. The full-wave analysis simulation, equivalent circuit model simulation, and practical measurement results reflect a high level of consistency.

Ku/Ka-Band Dual-Frequency Shared-Aperture Antenna Array With High Isolation Using Frequency Selective Surface

In this letter, a high-gain, high-efficiency, and high-isolation Ku/Ka-band dual-frequency shared-aperture antenna array using frequency selective surface (FSS) is investigated. The antenna consists of an 8×8 Ka-band and a 4×4 Ku-band printed double-sided dipole arrays in the upper and lower substrate layers, respectively. To realize high efficiency, the feeding networks are realized with double-sided parallel striplines. A low-pass FSS structure, sandwiched by the Ku-band array and the Ka-band array, works as the ground plane of the Ka-band array and is transparent to the Ku-band array, and it can also isolate the two antenna arrays for high isolations. In addition, a third-order impedance transform filter is integrated into the feed network of the Ka-band array. Ultimately, the antenna array has -10 dB impedance bandwidths of 14.47–17.52 GHz (19.07%) and 30.19–38.29 GHz (23.66%) with the peak antenna gain of 18.9 dBi at 16 GHz and 24.85 dBi at 35 GHz, respectively. High aperture efficiencies of 79% and 65% are realized. Meanwhile, the isolations between the two ports are better than 20 dB in low band and 30 dB in high band. For verification, a prototype is fabricated, and the measured results agree with the simulated ones.

A triple‐band frequency selective surface for 5G millimeter‐wave communications

AbstractIn this letter, a new triple‐band millimeter‐wave frequency selective surface (FSS) is presented. The proposed FSS structure consists of three slot‐based resonance mechanisms on the single layer of Rogers Diclad880 dielectric. It shows a high compactness with a unit cell surface area of 5.4 × 5.4 mm2. The proposed FSS exhibits a triple‐band bandpass filter characteristics for the allocated 5G millimeter‐wave frequency regions with sufficient bandwidths corresponding to 23.5–24.6, 27–28.5, and 37.5–41 GHz, respectively. Simulation outcomes reveal that the FSS poses polarization insensitive behavior, and maintains high transmission skill for a wide range of incident angles up to 40°. A 40 × 40 FSS panel is fabricated, and the experimental verification is carried out. The outcomes prove that the proposed FSS is suitable for multiband 5G millimeter‐wave filtering applications.

A Solution to the Dilemma for FSS Inverse Design Using Generative Models

Recently, artificial neural networks (ANNs) show a great potential in frequency selective surface (FSS) inverse design. However, it is inevitable to encounter the problem of non-unique mapping between inputs and outputs, which cannot be easily solved by the traditional ANNs framework. We analyze this existing dilemma from the perspective of information loss caused by data dimensionality reduction, and propose deploying generative models as a solution, for the first time. Specifically, two approaches with a novel model based on conditional Generative Adversarial Network (cGAN) are presented to achieve inverse design from the given indexes to FSS physical dimensions. By applying the proposed method, we can immediately obtain FSS design that meets the industrial demands without complex neural network processing or repeated iterations. Moreover, the proposed method is validated in closed-loop simulations and corresponding experiments, which also paves the way for designing complex FSS structures with desired electromagnetic responses using deep neural networks.

High gain and enhanced isolation MIMO antenna with FSS and metasurface

This research work proposes a high gain MIMO antenna with improved isolation. The present antenna is low profile and contains four elements built with FR-4 substrate. This antenna uses a superstrate based metasurface to reduce the coupling between antenna elements and frequency selective surface (FSS) to improve the antenna gain. The suggested antenna is topped with a superstrate-based metasurface, which is positioned at a height of 15 mm below the antenna. FSS structure consists of a concentric circular ring on a single-layered FR4 substrate. The present MIMO antenna has operating band of 1.18–2.89 GHz with a peak gain of 8.44 dBi and isolation of less than − 20 dB between each antenna element. This MIMO antenna provides maximum efficiency of 96% and 92.3% reduction in the correlation coefficient. Additionally, the current structure offers a diversity gain (DG) of 9.99 and an envelope correlation coefficient (ECC) of 0.01.

3-D Printed Dual-Band Frequency Selective Surfaces for Radome Applications

In this study, dual-band frequency selective surface (FSS) structures are designed by using 3-D printing technology for antenna radome applications. Four different configurations are studied to find the best alternative for FSS substrate not only for electromagnetic (EM) responses but also for its mechanical properties suitable for radomes. To ease the manufacturing process, a conductive paint is also studied instead of copper microstrip lines. In addition, graphite is also used for the comparison. Different 3-D printed configurations, various thickness values and three different materials for conductive part are examined and compared to find the most efficient radome structure.

Design of compact dual‐band shared‐aperture antenna system based on frequency selective surface

AbstractA miniaturized dual‐band dual‐polarization base station antenna array operating at 2.4–2.8 and 4.6–5.0 GHz is proposed in this paper. The upper‐band unit is embedded in the lower‐band unit to miniature the array size. The size of the proposed shared‐aperture antenna element is 0.28 × 0.28 . To ensure the normal radiation of dual‐band under the small frequency ratio, a meander slot frequency selective surface structure is introduced, which is electromagnetically transparent to the lower‐band unit and function as metal ground for the upper‐band unit to ensure the normal radiation of the upper and lower‐band units, respectively. Simulation and measured results show that the antenna array meets the following design specifications: dual‐band operating (voltage standing wave ratio [VSWR] < 2), mutual coupling less than −20 dB basically, satisfactory gain and radiation characteristics.

Bandwidth and Gain Enhancement of a CPW Antenna Using Frequency Selective Surface for UWB Applications

In this article, a single-layer frequency selective surface (FSS)-loaded compact coplanar waveguide (CPW)-fed antenna is proposed for very high-gain and ultra-wideband applications. At the initial stage, a geometrically simple ultra-wideband (UWB) antenna is designed which contains CPW feed lines and a multi-stub-loaded hexagonal patch. The various stubs are inserted to improve the bandwidth of the radiator. The antenna operates at 5-17 GHz and offers 6.5 dBi peak gain. Subsequently, the proposed FSS structure is designed and loaded beneath the proposed UWB antenna to improve bandwidth and enhance gain. The antenna loaded with FSS operates at an ultra-wideband of 3-18 GHz and offers a peak gain of 10.5 dBi. The FSS layer contains 5 × 5 unit cells with a total dimension of 50 mm × 50 mm. The gap between the FSS layer and UWB antenna is 9 mm, which is fixed to obtain maximum gain. The proposed UWB antenna and its results are compared with the fabricated prototype to verify the results. Moreover, the performance parameters such as bandwidth, gain, operational frequency, and the number of FSS layers used in the proposed antenna are compared with existing literature to show the significance of the proposed work. Overall, the proposed antenna is easy to fabricate and has a low profile and simple geometry with a compact size while offering a very wide bandwidth and high gain. Due to all of its performance properties, the proposed antenna system is a strong candidate for upcoming wideband and high-gain applications.

Flexible strain sensor based on a frequency selective surface.

Frequency selective surfaces (FSSs), modern artificial materials, show great potential in engineering applications due to their excellent frequency selection capabilities. In this paper, we introduce a flexible strain sensor based on FSS reflection characteristics, which can be well conformally attached to the surface of an object and bear mechanical deformation from a certain load. When the FSS structure changes, the original working frequency will be shifted. By measuring the difference in electromagnetic performance, the strain degree of the object can be monitored in real-time. In this study, we designed an FSS sensor with a working frequency of 31.4 GHz and amplitude that reaches -35 dB that exhibits favorable resonance properties in the Ka-band. The quality factor of FSS is 16.2, which indicates that the sensor has excellent sensing performance. The sensor was applied in the strain detection of a rocket engine case through statics and electromagnetic simulations. The analysis showed that the working frequency of the sensor shifted by approximately 200 MHz for 1.64% radial expansion of the engine case and the frequency shift exhibits an excellent linear relationship with the deformation in diverse loads, so it can be used for accurate strain detection of the case. Based on experiments, we carried out the uniaxial tensile test of the FSS sensor in this study. The sensor's sensitivity was 1.28 GHz/mm when the FSS was stretched by 0-3 mm in the test. Therefore, the FSS sensor has high sensitivity and strong mechanical properties, which verifies the practical value of the FSS structure designed in this paper. It has a broad development space in this field.

A New Ultraminiaturized Low-profile and Stable FSS with 2.5D Structure for 900 MHz ISM Band

This paper presents a new 2.5D ultraminiaturized frequency selective surface (FSS) structure to operate in the 900 MHz ISM band (902 to 928 MHz), for application in the Wi-Fi HaLow. The proposed FSS simulation and design are performed using ANSYS HFSS software and equivalent circuit model (ECM). The development of the proposed 2.5D FSS is based on meander-line-based conducting patches and has required the simulation and design of typical (2D) and 2.5D structures. An equivalent circuit model was proposed and presented very accurate results. For comparison purpose, a prototype is fabricated and measured. Agreement is observed between simulation and measurement results.

FSS embedded high gain ‘N’ shaped miniaturized broadband antenna

This research work represents a broadband (3.3 GHz − 17.85 GHz) high gain miniaturized (16 mm × 24 mm × 1.6 mm) microstrip patch antenna. Initially multiband property is achieved through ‘N’ shaped radiating patch surface and ‘I’ shaped ground plane surface. Finally broadband property is attained through better impedance matching by modifying feeding structure with a single step matching staircase structure. The presented antenna shows large −10 dB impedance bandwidth of 14.55 GHz with a percentage bandwidth of 138 %, Bandwidth Dimension Ratio (BDR) of 2970 and a peak gain of 4.45 dBi at 9.5 GHz. By embedding FSS (Frequency Selective Surface) structure having FSS unit cell dimension of 13 mm × 13 mm × 1.6 mm with the antenna at suitable distance, antenna gain has been elevated successfully across the entire operating frequency range (3.25 GHz–17.8 GHz). FSS coupled antenna exhibits highest gain improvement of 7.5 dBi at 3.5 GHz and peak gain of 9.1 dBi at 9.3 GHz. The FSS integrated antenna structure operates with elevated gain (peak gain of 9.1 dBi at 9.3 GHz) across the entire operating frequency range (3.25 GHz–17.8 GHz). All inclusive volume of the presented FSS coupled antenna is 52 mm × 52 mm × 21.2 mm, which can be successfully utilized in high gain broadband wireless applications. The antenna patch area miniaturization is calculated as 65 % with respect to lowest frequency of operation. The proposed FSS and antenna are developed and simulated by utilizing CST Studio Suite Software and equivalent circuit of the presented antenna is simulated utilizing ADS software. Both FSS and antenna are fabricated using inexpensive FR 4 substrate (1.6 mm thick, relative dielectric constant of 4.4 and loss tangent of 0.02) and Standard Microwave Test Bench is used to validate the antenna and composite antenna structure simulation results.

Development of a metamaterial‐based compact applicator for hyperthermia

AbstractA compact focused metamaterial‐based applicator is investigated for hyperthermia cancer treatment in this letter. The metamaterial‐based applicator consists of a double spiral antenna (DSA), an artificial magnetic conductor (AMC) as a reflector, and a frequency selective surface (FSS) as a lens. An AMC structure (64 × 64 mm2) is placed in the back of the antenna at a 5 mm distance that converges the bidirectional field pattern of the antenna into the directional field pattern. Further, to increase penetration inside the tissue, an FSS structure (64 × 64 mm2) is placed at the top of DSA at a distance of 4 mm. The FSS directs the energy toward the tumor location and provides a uniform heating pattern. The field and temperature distribution are numerically obtained for the proposed applicator in the heterogeneous phantom (layers of skin, fat, and muscles), and the performance of the applicator is evaluated in terms of the specific absorption rate, penetration depth, and effective field size. The performance of the applicator is also analyzed for a deeply placed (at 16 mm from the skin surface) irregular‐shaped tumor. The temperature profile calculates 44°C at an input power of 2.5 W. The results show that the applicator is capable of heating sufficiently deep‐seated tumors.