Frequency Selective Surface Array Research Articles

Interference effect of frequency selective surface on lightning attachment

Airborne electromagnetic functional devices represented by frequency selective surface (FSS) are receiving increasing attention due to the ever-growing complication of electromagnetic environment in air space. Previous investigations have highlighted the capability of FSS to induce the distorted electric field encompassing an airborne radome. This phenomenon interferes with lightning attachment behavior and compromises the effectiveness of anti-lightning devices. A current challenge is how to reveal the physical mechanism behind this interference. In this paper, a lightning model is established for a honeycomb sandwich composite-FSS structure and a single FSS array, respectively, to investigate the interference effect of FSS on lightning attachment. Arc behavior is verified by structural damage characteristics in relevant experiments. An equivalent circuit representing the process of an FSS array suffering a lightning strike is proposed to reveal the interference mechanism of FSS. The results indicate that the electrical connectivity of FSS has a significant impact on lightning attachment behavior. Patch FSS can induce partial discharge and exacerbate interface damage to a radome while aperture FSS eases energy accumulation, although the latter is prone to induce lightning leaders without integration with composites. The obtained results provide potential guidance for the structural and anti-lightning design of an airborne radome.

FSS inspired two port CP MIMO antenna with enhanced gain for X-band applications

In this work, a dual-port circularly polarized (CP) Multiple Input Multiple Output (MIMO) antenna equipped with frequency selective surface (FSS) for X-band applications is designed and analyzed. The antenna system aims to enhance gain, a critical parameter like isolation radiation pattern, etc. In wireless communication systems working in the X-band frequency range. The present MIMO antenna consists of two parts that provide coverage for the whole frequency band of 7.6–11.6 GHz, specifically for X-band communication applications. As a decoupled network, the meander line architecture greatly improves isolation. The MIMO antenna's measurements include 25 × 30 × 1 mm3. To improve the antenna's peak gain even further, a FSS is placed below the present MIMO antenna at 10.5 mm. The whole volume of the FSS-inspired composite structure is 50 × 60 × 11.6 mm3. By correctly incorporating the FSS array with the antenna's structure and utilizing its frequency-selective properties, gain improvement can be attained. Without FSS, the antenna's gain is 4.8 dBi and it is enhanced by 21 % and the maximum value of gain is 15 dBi in the desired frequency spectrum. The efficiency of the proposed FSS-inspired structure is >84.2% in the operating frequency band. To evaluate the MIMO performance of the current antenna, several attributes are evaluated. On the evaluation, it is found that the present MIMO antenna has an envelope correlation coefficient (ECC) < 0.004, a diversity gain (DG) over 9.99, measured mean effective gain (MEG) below 3 dB, and CCL of less than 0.4 bits/s/Hz throughout the resonant frequency spectrum. Through modeling and experimental testing, the current MIMO antenna model is created and verified.

Miniaturization of a Fully Metallic Bandpass Frequency Selective Surface for Millimeter-Wave Band Applications

This article presents a miniaturized all-metallic bandpass frequency selective surface (FSS) for millimeter-wave (mmWave) applications. The designed FSS is realized as a slot-type element that can be easily incorporated into all-metallic device architectures. The miniaturization is achieved by a convoluted or meander slot structure, i.e., a miniaturization technique borrowed from conventional substrate-based FSS design. It is demonstrated that the proposed FSS element provides a stable and wide bandpass performance from 24.9 to 31.4 GHz for both the transverse electric (TE) and the transverse magnetic (TM) polarizations at the broadside direction ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = 0^{\circ }$</tex-math></inline-formula> ). Adequate performance is maintained at oblique incidence angles up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = \pm \,45^{\circ }$</tex-math></inline-formula> . A 25 × 25-elements FSS array prototype has been manufactured using the cost-effective chemical etching technique and experimentally characterized utilizing a free-space measurement setup. The results demonstrate a remarkably good correlation between simulations and measurements. Hence, the proposed miniaturized FSS represents an excellent potential to realize an all-metallic FSS with low insertion loss, low profile, and wideband performance at low fabrication costs for mmWave applications.

Performance analysis of frequency selective reflectors based on rectangular loop pair for wideband applications

This paper presents performance analysis of single layered bandstop frequency selective surfaces (FSSs) for C-band and ultra-wideband (UWB) frequency ranges respectively. These FSSs are based on polarization dependent (PD) single rectangular loop pair (RLP). RLP arrays in square and rectangular grids are developed and simulated to evaluate signal rejection and reflection for incident transverse electric (TE) and transverse magnetic (TM) waves. Further, orthogonal patterns are printed back-to-back (BTB) on dielectric substrate to study wave propagation and effect on wave polarization. Non-linearities in the reflection phase of BTB arrays are then mitigated by printing orthogonal FSS arrays on the same side of the dielectric substrate. The equivalent circuit models (ECMs) of these FSSs are also presented to predict their transmission characteristics. Later, two FSSs with wideband and ultra-wideband rejection capability are developed and experiments are carried out. The array of merged RLP arranged in square grid exhibits stopband from 4.5 GHz to 8.4 GHz with polarization independence (PI) and it is angularly stable while merged array of RLP arranged in rectangular grid exhibit ultra-wide stopband from 2.3 GHz to 11.5 GHz but it is not angularly stable. The measured transmission responses of all FSSs proposed here are close to simulated results.

Conformal Frequency Selective Surfaces for Arbitrary Curvature

An algorithm is introduced for generating frequency selective surfaces (FSSs) capable of conforming to any curvature while maintaining the proper size, shape, and spacing of the elements. Compared to traditional projection and mapping methods, the presented algorithm maintains the electromagnetic properties of the FSS array despite the curvature. The algorithm can be used to conform to radomes, parts of autonomous vehicles, or any surface. The algorithm is agnostic to both element design and surface curvature. This allows the user to design a FSS for any curved surface while maintaining its response comparable to a flat array. The algorithm outputs two standard tessellation language (STL) files, one describing the curved surface and the other the elements of the FSS placed onto the curved surface. This makes the algorithm suitable for 3-D printing using systems with more than three axes or for flexible electronics. Several examples of arbitrary surfaces are shown. Lastly, the algorithm was applied to a Jerusalem-cross (JC) FSS on a nonsymmetrical parabolic dome. The dimensions of the parabolic dome were chosen to test the response of the array on a rather extreme surface against a projected array on the same surface. Simulations were carried out using Ansys HFSS from the infinite array to finite arrays to confirm the operation. Three test surfaces were manufactured with measured results found to be in good agreement with the simulation.

Use of Thermochromic Properties of VO2 for Reconfigurable Frequency Selection

The thermochromic nature of vanadium dioxide (VO2) has facilitated many promising applications for reconfigurable frequency selectivity. The phase-changing property of VO2 was used to realise a reconfigurable frequency-selective surface (FSS) capable of manipulating electromagnetic waves for different functionalities. Diffractive optical elements (DOE) are used for diffracting laser beams to form conductive FSS images on the VO2 wafer for frequency selectivity. The dipoles on the VO2 wafer generate a stop band response of 12 dB and 10 dB for unit cells of the single dipole and double dipole at 3.5 GHz, respectively. A 10 GHz FSS array is projected by DOE on the 2-inch VO2 wafer with a filtering effect of 13 dB at 9.5–10.5 GHz. This solution is used to design a radar cross-section (RCS) modification FSS with reflected waves of about 20 dB higher reflectivity in the backscattering direction than in the specular direction.

An electromagnetic shield design using frequency selective surfaces on a textile substrate

In this paper, a flexible bandstop frequency selective surface (FSS) array fabricated on jeans substrate using silver-coated conductive yarn with a computerized embroidery machine is presented for X-band. The S parameters of the fabricated design are measured through the free space method. The measured S-parameters showed significant stopband characteristics between 8 GHz and 11.5 GHz for −30°–30° wide incident angles. Moreover, the transmission, reflection, absorption, and shielding effectiveness (SE) of the FSS array are also computed using measured S parameters. The prototype provides SE of more than 30 dB in X-band and has dominant absorption behavior for some frequencies within the band.

Dual rhombic loop‐based frequency selective surfaces for X‐band applications

AbstractDual rhombic loop (DRL) based low‐cost X‐band frequency selective surfaces (FSSs) with stopband characteristics are presented in this study. Orthogonally oriented arrays of rhombic loop pairs are printed back‐to‐back (BTB) on both sides of dielectric substrate to achieve wide stopband characteristics with stable response under oblique incidences. The nonlinearities in the reflection phase of BTB DRL printed FSSs are compensated by printing orthogonally oriented rhombic loop pairs on the same side of the substrate. Merging orthogonally oriented rhombic loop pairs results in a single‐layer wide stopband FSS with linear reflection phase under normal incidence. Both polarization dependent merged DRL (MDRL) and independent BTB DRL FSSs are developed and experimentally validated. As per measurements, the BTB printed FSS array exhibits 4.3 GHz wide stopband with transmission nulls at 7.9 and 10 GHz while the single side printed FSS exhibits 3.7 GHz wide stopband with transmission null at 8.3 GHz.

On the Design of Ultralow-Profile Broadband Absorber Based on Non-Foster Circuit

In this letter, a novel and effective method for non-Foster active absorber with ultralow profile and wide absorption band is proposed. The three-layer absorber consists of a square loop frequency selective surface array printed on the FR-4 dielectric substrate, a non-Foster matching layer, and a backed metal plane.Equivalent circuit model for the active absorber is proposed and analyzed, providing great insight into the effect of non-Foster matching layer on breaking the Rozanov limit effectively. A 1×10 absorber absorbing structure sample is fabricated.It is shown by measurement that the absorber has a fractional bandwidth of 36.0%, with a total thickness of only 0.008 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> (wavelength at the lowest absorption frequency). The simulation and experimental results are in good agreement in the operating band, which verifies the accuracy of the design method.

A Frequency Selective Surface Loaded UWB Antenna for High Gain Applications

This paper presents the design of wideband and high gain Frequency Selective Surface (FSS) loaded antenna for ultra-wideband (UWB) wireless applications requiring high-gain. The antenna consists of a monopole and an FSS reflector. Initially, a conventional rectangular monopole antenna is modified using slot and stub to achieve wide operational bandwidth and size reduction. This modified antenna shows 50% miniaturization compared to a primary rectangular monopole, having a wide impedance bandwidth of 3.6–11.8 GHz. Afterward, an FSS is constructed by the combination of circular and square ring structures. The FSS array consisting of 8 × 8-unit cells are integrated with the antenna as a reflector to enhance the performance of the proposed miniaturized UWB antenna. The loading of FSS results in an improvement of at least 4 dBi gain in the entire operational bandwidth. Moreover, the antenna's bandwidth is also increased at the lower frequency band due to the presence of the FSS. A prototype of the antenna is fabricated and tested to verify the simulation results. The simulation and measurement results show that the antenna offers a wideband –10 dB impedance bandwidth ranging from 2.55–13 GHz with a stable peak gain of 8.6 dBi and retains the radiation pattern stability.

Directional and isolated UWB‐MIMO antenna‐based uniplanar UWB‐FSS array and T‐strip for bi‐static microwave imaging: Baggage‐scanner

This article presented a novel compact multi-input-multi-output (MIMO) hexagonal monopole antenna with a uniplanar compact frequency-selective-surface (FSS) array for microwave imaging (MWI). The ultra-wideband (UWB) dual-element linear MIMO antenna was designed on the FR4 substrate with 50 Ω coplanar waveguide feed, T-strip isolation, novel numerical calculation and equivalent circuit analyses. The main issues of realising high-resolution images based on planer UWB antenna for MWI are the low gain, omnidirectional pattern, design size and mutual coupling of MIMO design. A novel technique was proposed to solve a hybrid issue (mutual coupling) of the MIMO reflected-waves from the FSS array and direct-wave. The uniplanar UWB-FSS unit cell was compacted by combining a square-loop and cross-dipole with a size of 0.095λ × 0.095λ. The novel-isolated UWB-MIMO antenna and UWB-FSS array (IMAF) were integrated, after investigating the distance between the antenna and FSS. The fabricated IMAF with a stable gain improvement of 4.5 dBi higher than the antenna without FSS, directional radiation pattern, size of 30 × 73.8 × 21.6 mm3 observed that a low mutual coupling of −27 dB, and operation bandwidth of 3.0–11.7 GHz. Moreover, a handbag was scanned experimentally via the bi-static approach to detect a small concealed object. The MWI system based on the MIMO antenna with FSS was displayed image resolution of 55% higher than that of MIMO antenna without FSS. The new baggage-scanner approach confirmed that the proposed MIMO antenna with FSS array can lead the humanity for healthy MWI applications.

유동환경용 FSS 전극 유전체 장벽 방전 구조 플라즈마 발생기의 X-Band 내 RCS 감소 효과

In this study, an frequency selective surface (FSS) electrode of a dielectric barrier discharge (DBD) plasma generator, with a two-dimensional planar target, for radar cross section (RCS) reduction is proposed and measured. The electrode of the proposed plasma generator is based on a cross FSS array conductor. Therefore, it is possible to minimize the amount of RCS change according to the efficient plasma discharge and polarization of the signal from the radar. In addition, a frame of FR-4 dielectric material is placed between the 4.572 mm gap of the ground surface and the electrode to reduce RCS owing to stable plasma discharge in a fluid environment in which the aircraft operates. The proposed plasma generator is fabricated to determine the optimal plasma discharge and RCS measurement. The measurement results showed a 2.9 dB RCS reduction in the X-band.

On the Design of Wideband Absorber Based on Multilayer and Multiresonant FSS Array

In this letter, a novel and effective design method for multilayer and multiresonant absorbers is proposed. The two-layer absorber is composed of two resistor-loaded square loop frequency selective surface (FSS) arrays printed on the Rogers 4003 dielectric substrate and a backed metal plane. Equivalent circuits for two-layer absorbers with resistive sheets and resonant FSSs are proposed, analyzed, and further improved to provide great insight into the existence of the four resonances and ultrawide bandwidth. In the equivalent circuit model, the substrate is transformed to a parallel admittance and a positive susceptance is introduced in the whole operation band, which contributes to an extra resonance. After the measurement of a fabricated sample, a fractional bandwidth of 171.2% is obtained for at least 10 dB reflection reduction, with a total thickness of only 0.087λL (wavelength at the lowest absorption frequency). The good agreement between the calculated, simulated, and measured results validates the designed absorber.

Mechanically Reconfigurable Frequency Selective Surface for RF Shielding in Indoor Wireless Environment

A novel polarization-independent reconfigurable frequency selective surface (FSS) for RF shielding is proposed in this letter. The FSS is designed on a flexible and transparent polyester film for shielding Wi-Fi frequency. The symmetrical cross dumbbell design of FSS helps in achieving alike bandstop response for both TE and TM modes with wider angular stability up to 60°. A finite prototype containing 15 × 11 elements is fabricated and tested. The FSS provides the measured shielding effectiveness of 32 dB at 5.2 GHz. Additionally, for RF shielding in an indoor wireless environment, Venetian blind inspired shutter mechanism is introduced in the designed FSS array. By rotating the blinds of the array, frequency tuning is achieved.

Performance improvement of a slotted square patch antenna using FSS superstrate for wireless application

This paper presents a wideband planar antenna integrated with a frequency selective surface (FSS). Initially, the FSS array screen is investigated using a basic square ring to construct a unit cell of the FSS periodical structure with a (12x12) array. FR4 with a permittivity of 4.7 and a thickness of 1.6 mm is used as the substrate material for both FSS structure and antenna. Then, the antenna is placed closely parallel over the FSS configuration at a distance of 28 mm. After analyzing the performance of the antenna in terms of return loss, directivity and antenna gain, the design is integrated with the FSS structure in order to achieve a stable frequency response. Directivity and gain improvement of 6.5 dB and 5.1 dB respectively are observed along broadside direction.

Twenty‐eight‐gigahertz beam‐switching ridge gap dielectric resonator antenna based on FSS for 5G applications

A new design of the double dielectric resonator antenna (DRA) fed by a printed ridge gap waveguide for beam-switching applications based on frequency selective surfaces (FSSs) is presented here. The dual-sided printed FSS element works in its reflection mode and comprises a slotted square C-shaped patch on the top layer and a square strip on the back plane. Therefore, the beam switching can be implemented by loading the proposed FSS array over and in the middle of DRAs. Loading the antenna with two layers of 3 × 3 FSS unit cells results in ±77° beam switching and a 3.16 dBi gain enhancement at 28 GHz. Simulation and measurements confirm the operation of the proposed antenna, with good matching and gain observed.

Design of a hybrid A-sandwich radome using a strongly coupled frequency selective surface element

AbstractThe airborne radomes have to cater superior electromagnetic (EM) performance with bandpass characteristics of stealth application. In this regard, a hybrid A-sandwich radome is proposed in this paper. The proposed radome consists of a novel strongly coupled frequency selective surface (FSS) core sandwiched between two dielectric layers (acts as skin) to form an A-sandwich structure. The dielectric layers are cascaded in such a way that the middle layer has less dielectric parameters than the skin dielectric. The core layer comprises a modified FSS array using strongly coupled FSS layers through a series of metallic vias. This strongly-coupled FSS element will have the advantage of eliminating inter-element interference and improves the EM performance characteristics of the structure. The structure exhibits very good band-pass characteristics (&gt;90%) at a normal impinging angle with sharp roll-off characteristics. To show the efficacy of the proposed structure, the transmission loss has been compared with that of conventional A-sandwich radomes at 0°, 50° incidence angle for both TE and TM polarization. Conformal analysis of the unit cell has been carried out, and sector-wise thickness optimization was performed to analyze the structure for the conformal shaped radome application. Finally, a physical prototype has been fabricated and measured its scattering parameters, radiation characteristics in a fully shielded anechoic chamber. The results are encouraging and prove its suitability for radome application.

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.

Reducing the RCS of a MIMO antenna using an angularly stable FSS

A systematic design procedure for reducing the radar cross section (RCS) of a multiple-input multiple-output (MIMO) antenna is presented in this paper. The RCS reduction was achieved at 11.3 GHz, which was out-of-band compared to the antenna's working frequency of 2.18 GHz. The design flow started with developing an isolation-enhancement network for the MIMO antenna that did not disturb the RCS reduction process. An incident- and polarization-angle-insensitive frequency-selective surface (FSS) was next designed. The conventional ground plane of the MIMO antenna was replaced by an FSS array. The designed FSS was introduced in such a way that the antenna's characteristics and isolation among the antenna ports were preserved by achieving the RCS reduction of an antenna at the bandpass frequency of the FSS. The proposed FSS was angularly stable, and hence an almost constant RCS reduction was found for most of the incident angles. The final proposed low-RCS MIMO antenna was fabricated and measured to validate the simulation results.

Reconfigurable RCS Reduction from Curved Structures Using Plasma Based FSS

The radar cross section (RCS) reduction from curved surfaces using plasma based frequency selective surfaces (FSS) is investigated. A frequency reconfigurable plasma based FSS unit-cell element with target-shaped structure is proposed. The operating frequency of the FSS is governed by the plasma ionization degree (i.e. plasma frequency). zero crossing frequency of the FSS unit-cell has a tuning range extending from 9.6 GHz to 11.3 GHz with an average bandwidth of 1.1 GHz. Planar and curved metallic surfaces are investigated. The curves structures include cylindrical (convex and concave), and spherical (convex and concave) surfaces. Single ionization source is applied at the rare end of the plasma FSS array design is optimized to maintain uniform plasma flow over the metallic surfaces by applying a single ionization source at the rare end of the array. The plasma FSS arrangement with ωp = 9 × 1011 rad/Sec loading a planar sheet reduces the RCS by 23 dB at 10.2 GHz and the (− 5 dB) frequency band of 14.7% for planar plate compared with the unloaded plate case. Different hybrid arrangements are investigated for wideband RCS reduction of 36.4% by superimposing reduction bands of three different plasma frequencies. A 21.5 dB reduction is achieved at 9.8 GHz for FSS arrangements (III). The effect of changing the radii of curvature for convex and concave cylindrical and spherical metallic surfaces is studied at different plasma frequencies. A full-wave analysis of the loaded metallic plates with plasma FSS is used to calculate the backscattered and bistatic RCS for different surfaces.