Frequency Selective Surface Structure Research Articles

A simple frequency selective surface structure for performance improvement of ultra‐wideband antenna in frequency and time domains

This article demonstrates a new type of annular ring shaped cylindrical dielectric resonator (ARCDR) loaded printed ultra-wideband (UWB) antenna which is further loaded with a new type of two-layer UWB frequency selective surface (FSS) structure. The proposed FSS helps to improve the peak gain of the standalone hybrid antenna significantly (about 4.45 dB). The proposed FSS loaded hybrid antenna provides measured impedance bandwidth (IBW) and measured peak gain about 115.5% (S11 ≤ −10 dB, 3.75 to 14 GHz) and 10.3 dBi respectively. The top layer of FSS structure employs a square loop configuration integrated with “+” sign, staged in 45° angle. Bottom layer of FSS consists of a square loop. The standalone proposed FSS structure also provides large transmission (S21 ≤ −10 dB, 108%, measured) bandwidth (BW) from 3.5 to 11 .75 GHz. The behavior of the proposed UWB antenna geometry has been studied in both frequency and time domains. The newly proposed FSS structure and integrated antenna have been fabricated and there is a close agreement between the simulated and the measured performances.

A Comparison of Simulated and Measured Data for an FSS Structure using FEKO in the X-Band

The advent of Frequency Selective Surfaces (FSS) has appeal for applications that may need to inhibit or permit the transmission of a frequency band through a surface. This paper compares the simulated transmission and reflection properties of an FSS structure (i.e., a Jerusalem Cross) from the standpoint of simulated and measured data. All simulations were done using FEKO.

Design Optimization of Ultra Wide Band Vivaldi Antenna Using Artificial Intelligence

In this work, computationally efficient design optimization of Frequency Selective Surface (FSS) loaded Ultra-wide band Vivaldi antenna is studied. The proposed design consists of a multi-layer FSS structure aimed for performance improvement of the Vivaldi design, which makes the design a multi-objective multi dimension optimization problem. For having a fast and accurate optimization process, a data driven surrogate model alongside of meta-heurists optimizer Honey Bee Mating Optimization had been used. The obtained results are compared with 3D EM full wave simulator. Results show, the obtained FSS loaded structure have enhanced directivity compared with the design without FSS structure, without any performance losses in the return loss characteristics. The FSS loaded Vivaldi antenna operates at 2–12 GHZ band with a maximum gain of 10 dBi at 10 GHz which makes the design a good solution for RADAR applications.

Active Frequency Selective Surface Absorber With Point-to-Point Biasing Control System

A frequency selective surface (FSS) absorber with a biasing control system is presented in this letter. The absorber consists of the top-layer FSS structure, the bottom-layer metal sheet, and an air spacer in between. The biasing circuit is controlled by a single-chip microcomputer with constant current outputs and each output port is connected to one p-i-n diode, which is employed to realize different absorption bands by controlling the induced current distribution. Both simulated and measured results demonstrate that fast switching function can be realized within certain frequency ranges (3.62-5.35 GHz and 7.92-9.27 GHz) with the absorption depth below -10 dB.

Design of high gain broadband microstrip patch antenna for UWB/X/Ku band applications

A miniature (20 mm × 14 mm × 1.6 mm) microstrip line fed broadband antenna with high gain is proposed in this research work. The proposed antenna exhibits −10 dB impedance bandwidth of 19.5 GHz (5 GHz-24.5 GHz) with a fractional bandwidth of 132% which covers major portion of UWB band (3.1 GHz −10.6 GHz), X band (8 GHz-12 GHz), Ku band (12 GHz-18 GHz) and large part of K band (18 GHz-27 GHz).A single layer frequency selective surface (FSS) is integrated with the proposed antenna to enhance the gain of 5.9 dBi over the entire frequency band. 6 × 6 FSS layer (52.8 mm × 52.8 mm × 1.6 mm) is kept below the proposed antenna at suitable distance without hampering the reflection coefficient and flat gain characteristics of the antenna. Proposed antenna and FSS structure are designed and simulated by using CST Microwave Studio simulator and both are built on FR-4 substrate of 1.6 mm thickness with relative dielectric constant (εr) of 4.4, loss tangent (tanδ) of 0.02. The overall dimension of the proposed FSS integrated antenna is 52.8 mm × 52.8 mm × 21.2 mm, which is highly relevant for high-gain applications. Simulated results are validated experimentally by standard Microwave Test bench.

Multistate active control RCS signature for the continuous adjustment absorber/reflector transformation applications.

Smart structures with tunable electromagnetic characteristics are required for camouflaging high-value targets, such as land warfare moving equipment, in continuously changing complex electromagnetic environments. The targets must control their radar cross section (RCS) to avoid detection and tracking. Frequency selective surfaces (FSSs) are the next-generation smart structures in which active RCS control is realized via impedance loading. In this paper, a multistate transformable FSS absorber/reflector that operates in the 3.9-11.0 GHz band is introduced and analyzed. The reflectivity amplitude of this absorber/reflector could be smoothly changed from 0 to -10 dB in 6.0-8.0 GHz. Each unit cell of the FSS structure consisted of four symmetrical diamond-shaped patterns, and the adjacent units were connected by PIN diodes. The absorption intensity of the FSS could be changed from 0 to -10 dB by adjusting the PIN bias voltage, which was applied via a simple bias network. The multistate switching characteristic of the FSS was verified by simulations and measurements. The results showed that adjustable absorbing intensity and switchable working states are the desirable characteristics that allow high-value targets to adapt to changing electromagnetic environments. Our work will bridge the gap between the available stealth strategies and practical applications, such as moving stealth vehicles.

Design and Analysis of Frequency Selective Surface for Ism and Lower Ultra-Wideband Antenna

A Compact, dual-layer Frequency Selective Surface (FSS) is presented for electromagnetic shielding applications. The square loop FSS is modified to provide band rejection characteristics for ISM band and lower Ultra-Wide Band (UWB) covering from 2.2 GHz to 7.1 GHz with the bandwidth of (S21 < -20dB) 4.9 GHz. The novel design exhibits symmetric property due to which it achieves polarization-insensitive stable band rejection of the desired frequency band for various angles of incidences up to 60°. The proposed FSS structure has compact dimensions of 0.170λ x 0.170λ x 0.0117λ. The design was fabricated on either side of the substrate made of FR-4 with a dielectric constant of 4.4 and loss tangent of 0.02. The measured results are well per the simulation results. The proposed FSS in this paper has various applications, including the aerospace industry, hospitals, random, and in the scope of electromagnetic filters, etc.

Device modeling of RF varactor diodes for adjustable microwave reflectivity in active frequency selective surfaces

At present, the design of absorbers with broadband electromagnetic absorption performance in the P/L band (0.3 ∼ 2 GHz) is a huge challenge. The frequency selective surface (FSS) loaded with active RF devices utilizes the characteristics of electrically adjustable device parameters, thereby a P/L band broadband active FSS absorber can be designed. It is obvious that device parameter characteristics are crucial to design excellent absorbing performance. Unfortunately, due to the industrial packaging characteristics of the current application of surface mounted devices, there are parasitic parameters in addition to the main impedance parameters. Here, an equivalent circuit model of a varactor diode is proposed. We combine thru-reflect-line calibration technology and advanced design system fitting to obtain the parasitic parameter values. Then a classic FSS structure is used to verify the consistency of the simulation and measurement for the varactor diode model. We hope that the model of the varactor diode we proposed will help the design of the new broadband adjustable absorber in the P/L band.

Designed band-pass frequency selective surfaces with thermal transparency

Band-pass frequency selective surfaces (FSSs) have been wildly used to achieve stealth performance for radar electromagnetic wave detection. However, the existence of air slots will lower the effective thermal conductivity of the FSS structure that distorts the external temperature field and makes the FSS infrared visible. An interesting and practical challenge for the development of FSSs is the feasibility of empowerment of both microwave frequency and thermal transparency. Based on the mechanism of periodic interparticle interaction, a periodic filled region is introduced to achieve thermal transparency. The design principle is discussed in detail, and typical Jerusalem cross shape aperture samples are selected for modeling simulation and experimental verification. The results of frequency response and heat transfer characteristics confirm the designed band-pass FSSs have less-distortion frequency response and thermal transparency, which provide an effective approach for the design and fabrication of microwave and infrared camouflage with easy implementation in practical applications.

Tunable liquid crystal frequency selective surface with the compact unit cell, large tuning range, and the passband of flat-top and sharp roll-off

In this paper, a design method for tunable liquid crystal (LC)-based frequency selective surface (FSS) with the compact unit cell, large tuning range, and the passband of flat-top and sharp roll-off is proposed. A very compact LC-based bandpass FSS unit cell with the dimension of 0.077 λ × 0.077 λ is designed based on a pair of planar vortex-shaped metallic structure with two large parallel patches, between which the LC is sandwiched. Results show that the central frequency of the FSS is tuned from 11.56 to 12.58 GHz, and the tuning range reaches up to 8.5%. In order to obtain the transmission characteristics of flat-top and sharp roll-off, a double-layer structure is proposed and combined with the LC-based FSS design. Theoretical analyses are conducted to declare the working principle of the double-layer LC-based FSS. A prototype sample for the double-layer LC-based FSS is designed and fabricated. Results show that the double-layer LC-based FSS structure achieves frequency selective characteristics with a flat-top passband of about 450 MHz and sharp roll-off for arbitrary LC states with −15 dB rectangle coefficient of 2.44 for arbitrary LC states. Moreover, stable frequency responses of the double-layer LC-based FSS under various incident angles from 0° to 45° are obtained for arbitrary LC states.

A wideband high gain trapezoidal monopole antenna backed by frequency selective surface

AbstractIn this paper, a wideband, high gain planar trapezoidal monopole antenna based on single‐layer frequency selective surface (FSS) is presented. The antenna adopts an unconventional, dual‐metallic on a single‐layer FSS structure as a reflector layer to improve its performance. To validate the structure, the prototypes are fabricated and measured. The experimental results exhibit that the operating band of the proposed antenna covers 3.52–5.92 GHz, which corresponding to the impedance bandwidth of 50% with respect to the 5 GHz is the center frequency. Moreover, the proposed antenna offers a high gain with the maximum gain of 11.8 dBi at 5.1 GHz, and the gain is sustained higher 10.5 dBi for the entire bandwidth. The proposed antenna structure is a potential candidate for wideband applications and wireless local area network applications.

Enhancing 5G antenna performance by using 3D FSS structures

In this work, an enhanced 3D frequency selective surface (FSS) patch antenna is proposed for 5G applications. A 23 to 26 GHz patch antenna was first designed before improving its performance by adding a 3 × 5 unit cell two-layer 2D transmission FSS structure. Then, reflective walls were placed on the side edges of the obtained structure in order to focus the incident field towards the main lobe; the aim being to build a 3D FSS structure without requiring the 3D printing technique. The total size of the obtained antenna is of 40 × 40 × 14 mm3. A comparative study was carried out between the performances of the patch antenna, the 2D FSS antenna and the 3D FSS antenna. A good agreement was observed between simulated results and measurements. An improvement of almost 3 and 2 dBi was obtained compared to the 2D FSS case, respectively, in simulated and measured results, while the side lobes in radiation patterns were decreased by more than 4 dBi, which confirms the adequate proposed design in switching to 3D structures.

Synthesis analysis of frequency selective surface using the generalized sheet transition conditions

Based on the generalized sheet transition conditions (GSTCs), the surface electric/magnetic susceptibilities of frequency selective surface (FSS) are extracted and analyzed. Key factors that affect the FSS performance, including frequency variations, structure shapes, angular dependent, and bandwidth are studied through the susceptibility parameters. Based on the analysis of four typical FSS structures, potential automatic structure designs are suggested and several illustrative examples are given. Finally, the method is compared with the equivalent circuit method.

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.

Investigation on MIMO antenna for very low ECC and isolation characteristics using FSS and metal-wall

A closely coupled (minimum distance of 0.14 λ0) Multiple Input Multiple Output (MIMO) antenna with high isolation is proposed. The MIMO antenna comprises of two circular-shaped radiating elements, which are fed by two opposite directed microstrip lines. The ground plane consists of modified Z-shaped metallic plane. Two different techniques are explored for improvement of isolation of MIMO antenna. First, a double ring structured frequency selective surface (FSS) is positioned above the antenna. The combination of FSS & antenna structure works with high isolation (S21or S12) (peak isolation of 49 dB) across the entire operating range (3.8 GHz–5.3 GHz). Secondly,arectangular metallic plate of thickness 0.3 mm is placed vertically between the MIMO antenna, which covers 4 GHz–5.3 GHz bands with high isolation (peak isolation of 49.4 dB). The proposed design consists of the MIMO antenna with both FSS and metallic plate. The proposed structure provides an appreciably high isolation (peak isolation of 59.5 dB) and peak gain of 4 dBi with Envelope Correlation Co-efficient (ECC) lower than 0.004. The proposed antenna having dimension of 40 mm × 40 mm is tremendously suitable for high isolation wireless applications.

Angle and polarization-independent miniaturized UWB FSS design

AbstractA single-layer ultra-wideband (UWB) stop-band frequency selective surface (FSS) has several advantages in wireless systems, including a simple design, low debugging complexity, and an appropriate thickness. This study proposes a miniaturized UWB stop-band FSS design. The proposed FSS structure consists of a square-loop and metalized vias that are arranged on a single layer substrate; it has an excellent angle and polarization-independent characteristics. At an incident angle of 60°, the polarization response frequencies of the transverse electric and magnetic modes only shifted by 0.003 f0 and 0.007 f0, respectively. The equivalent circuit models of the square-loop and metallized vias structure are analysed and the accuracy of the calculation is evaluated by comparing the electromagnetic simulation. The 20 × 20 array constitutes an FSS reflector with a unit size of 4.2 mm × 4.2 mm (less than one-twentieth of the wavelength of 3 GHz), which realizes an UWB quasi-constant gain enhancement (in-band flatness is &lt;0.5 dB). Finally, the simulation results were verified through sample processing and measurement; consistent results were obtained. The FSS miniaturization design method proposed in this study could be applied to the design of passband FSS (complementary structure), antennas and filters, among other applications.

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.

FSS superstrate antenna for satellite cynosure on IoT to combat COVID-19 pandemic

The global pandemic, COVID-19 needs joint techniques and technology to combat it. The internet of things (IoT) has been at the forefront in solving problems, not only in the health care sector but in other sectors. It delivers accuracy with robustness in the developing service and application. However, it remains clear that the use of IoT is limited to coverage, longevity, security, connectivity issue, immediacy, and multicasting, we proposed in this paper frequency selective surface (FSS) as superstrate for rectangular microstrip antenna. An FSS design combine with the rectangular microstrip antenna for better performance is placed over FSS parallel configuration. The rectangular microstrip antenna was titled 45 degrees to change the band-stop. Analysis of the proposed performance in terms of gain, return loss, and directivity shows that the FSS structure's integration brings better results. With the help of a 3D electromagnetic computer simulation technology CST studio suite, we model the proposed antenna, perform the simulation with a frequency-domain solver, and validate it with a time-domain solver. The proposed impressive result is suitable for satellite networks, which hybrid with IoT can provide a sustainable long-time solution in fighting the COVID-19 pandemic.

A Dual‐Frequency Miniaturized Frequency Selective Surface Structure Suitable for Antenna Stealth

A tiny dual‐band frequency selective surface structure is proposed in this paper. With dual‐band rejection characteristics at the corresponding frequency points of the S‐band and C‐band, suitable for antenna stealth. To achieve miniaturization, the unit‐cell architecture resembles the shape of a “S.” First of all, the author describes the parameters of the surface element, and then, the transmission characteristics of the surface element are analyzed by the equivalent circuit method. By maintaining a constant response to TE and TM polarization patterns and oblique incident angles, the suggested device ensures angular independence. The measured findings from the constructed FSS are used to validate the computed results. Finally, a new unit structure is provided for the application of FSS in antenna stealth.

A Novel Miniaturized Ultra-Wideband Frequency Selective Surface With Rapid Band Edge

This paper presents a novel frequency selective surface (FSS) structure with miniaturized, rapid band edge, ultra-wideband passband, and ultra-wideband out of band shielding. The proposed FSS is formed by using two air foam layers to cascade three single layers with the unit cell dimension in 6mm×6mm(0.0234λ×0.0234λ). The corresponding equivalent circuit models are developed for interpretation on the physical mechanism and formulate the relevant design equations. Finally, a prototype of the proposed structure is fabricated and measured to verify the full-wave simulation, and theoretical analysis results. The measured results show the proposed FSS has a -3 dB passband from 1.17 GHz to 7.08 GHz and a -10 dB stopband from 7.34 GHz to 15.0 GHz. The calculated relative bandwidth is 143.3% and 68.6%, respectively, which exhibits the stable performance against the variation of the incident angles from 0° to 45° for both TE and TM polarizations. All these results demonstrate that the proposed FSS is suitable for the actual miniatur-ized EMI shielding scene application.