Multiband 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.

Ultra-thin freestanding terahertz frequency selective surface on flexible cyclic olefin copolymer

Frequency selective surfaces (FSSs) are widely employed in spectrometers, selective absorbers, energy harvesting, and sensing devices. However, in the terahertz range, the performance of this ideal component is frequently constrained by the choice of material, which introduces a certain degree of attenuation, thereby diminishing the signal-to-noise ratio. Moreover, these FSS are often bulky and demonstrate a low extinction ratio, which limits their usage in wearables and miniaturised devices. In this work, a multi-band FSS composed of periodic microstructures on an ultrathin cyclic olefin copolymer sheet is proposed, analysed, fabricated, and evaluated using terahertz-time domain spectroscopy. The unit cell is composed of triple, evenly spaced, horizontal gold strips, linked around the middle by a fourth vertically oriented gold strip. By displacing the vertical strip, the asymmetric metasurface shows dual narrowband transmission at 1.04 THz and 1.67 THz. However, only a single narrowband transmission at 1.07 THz can be observed on a symmetric metasurface, with no displacement. The calculated Q factors are 4.52 and 16.63 at 1.04 THz and 1.67 THz, respectively, for the asymmetric metasurface. While for the symmetric metasurface, the calculated Q factor at 1.07 THz is 3.63. The proposed flexible metasurface can be tailored easily as single or dual narrowband frequency selective metasurface for channel filtering and broadband sources in emerging terahertz wireless systems.

Design and characteristic analysis of uniplanar multiband frequency selective surface for GSM, LTE, WLAN, ISM, WiMAX and X‐band applications

AbstractThe uniplanar compact, affordable, and unique slot‐based multiband frequency selective surface (FSS) of periodic cell size 0.14λc × 0.14λc (λc is wavelength at the initial stopband resonance) is presented in this article. The quadband FSS is analyzed using full‐wave simulation, circuit simulation (ECM), and experimental measurement where good agreement is attained. The FSS offers polarization independence with steady responses for all angular variations in the TE plane and up to 45° in the TM plane. The FSS offers dual stopbands at 2.75–4.15 and 9.45–12.48 GHz and dual passbands at 0.001–0.8 and 4.74–5.6 GHz that includes spectrum coverage of GSM, LTE, WLAN, ISM, WiMAX, and most part of X‐band communication.

A modified Jerusalem inspired bandpass FSS for multiband applications based on concentric ring slots

Abstract This paper presents the design of a multi-band planar bandpass Frequency Selective Surface with the novel rings and a modified Jerusalem cross integrated structure. To begin, the proposed FSS array geometry is defined by constructing a unit cell size of order of 0.57 λ 0 × 0.57 λ 0 where λ 0 represents free-space wavelength of the first resonant frequency of the FSS periodic structure using novel concentric rings, leading to low profile design. The array structure is fabricated on the substrate material FR4 with a permittivity of 4.4 and having a thickness of 0.8 mm. Combination of concentric rings and Jerusalem Integrated Structure is examined. Low-profile, simpler design, improved angular and polarization stability are all benefits of the proposed FSS. The proposed FSS structure is designed to obtain a stable frequency response over entire Ku band. The simulated and experimental results are measured in a free space measurement setup, which indicate resonances at 12.39 GHz, 14.63 GHz, 16.11 GHz and 17.82 GHz, exhibits supported band pass frequency ratio 1.43 for Ku band applications. The simulated, equivalent circuit model and experimental results showed that the experimental results agree well with the simulated results for both TE (Transverse Electric) mode and TM (Transverse Magnetic) mode of polarization.

Arbitrary polygon shape optimization applied to multiband frequency selective surface inverse design

An arbitrary polygon shape optimization method is proposed for multiband frequency selective surface (FSS) inverse design in this paper. Different from the traditional deterministic methods, our approach uses the relationship between lumped parameter of equivalent circuit model (ECM) and distribution parameter which can readily determine the search direction. Meanwhile, the iteration step size is determined by the normalized current density. Polygon representation of FSS element can improve the degree of freedom of structural optimization to a great extent compare with parameterized method. This approach has the ability to avoid the conflict of multi-objective optimization and optimize multiband FSS effectively and accurately. A dual-band FSS is taken as a case to verify the method. The simulation results of optimized structure meet the expectation and are basically coincident with measurement results, thus verifying the feasibility of the optimization method.

Miniaturized multiband frequency selective surface with wide frequency ratio

AbstractThis article presents the design of a novel miniaturized 2.5D frequency selective surface (FSS) for radiofrequency and microwave shielding applications is proposed. The proposed FSS is configured to offer multiple band‐stop characteristics with a wide frequency ratio. The unit cell is developed using traces that run on the top and bottom layers of the substrate with traces connected using vias. This proposed unit cell structure provides distinct operating modes at high and low frequencies. The proposed FSS unit cell has a compact geometry with a foot‐print of 0.059λo × 0.059λo where λo is the freespace wavelength. The FSS unit cell is polarization insensitive and exhibits good angular stability up to 45°. A prototype FSS is fabricated to validate the simulation results. The miniaturized FSS can be used as a shield at terrestrial frequencies and satellite frequencies making it usable for both indoor and outdoor environments.

Miniaturized multi-band frequency selective surface with angular and polarization independent characteristic

Abstract This paper presents a miniaturized multi-band frequency selective surface for band-stop applications. The proposed design is evolved from a modified swastik structure with L-shaped arms printed on FR4 substrate. The structure is designed to operate at 2.4, 5.8, 8.6, and 10.8 GHz covering Wifi, WiMAX, and X-band applications. The proposed quad-band FSS has an overall unit cell size of 0.084 λ0 × 0.084 λ0, where λ0 is the wavelength of the lower operational frequency. The symmetric FSS structure provides the advantage of polarization independency. It also exhibits a stable frequency response up to 60° for both the horizontally polarized EM waves (Transverse Magnetic Mode) and the vertically polarized EM waves (Transverse Electric Mode). Moreover, measurement results obtained from the fabricated prototype are compared with the simulation results and are found to be in close agreement with each other. Single layer structure, compact, and coverage of multiple applications are the advantages of the proposed multiband FSS.

A Novel Double-layer Low-profile Multiband Frequency Selective Surface for 4G Mobile Communication System

A novel double-layer multiband, low-profile frequency selective surface (FSS) for IMT-Advanced (4G) mobile communication system is presented in this article. On aspired to a minimum transmission coefficient of −10 dB for surface materials when the frequency bands targeted for blocking are stopped. For this project, we chose the dielectric substrate FR4 (loss-tangent = 0.02; dielectric constant = 4.54) and a thickness of 1 mm. Dodecagonal rings, upright bars, and square frame make up the FSS unit cell. The desired frequency responses of the FSS were intended to avoid being changed according to the angle of incidence of the electromagnetic waves. The FSS design is proposed as a symmetrical structure to make it polarization-independent and is aimed to stop 800, 900, 1800, 2100, and 2600 MHz frequencies to prevent harmful effects to human health and interference effects at these frequencies. With a cell size of 0.17λ, the planned FSS is quite small and, thus, has a low sensitivity at the angle of the incident wave. In addition, FSS geometry was manufactured by a printed circuit board (PCB) and measured in a non-reflective environment after being studied in Ansys high-frequency structure simulator (HFSS) software. By comparing the analysis and measurement results of the design, the success of the FSS to the frequencies to be stopped has been verified. The effect of each patch on different frequencies has been examined by drawing the surface current density graphs of the design.

A Multiband FSS Director Using Aperture Interdigital Structure for Wireless Communication Systems

This research paper proposes a multi-band frequency selective surface (FSS) director using the aperture interdigital technique. The FSS unit cell has been designed based on a basic bandpass filter (BPF) connected with an interdigital structure. With the proposed structure, the FSS unit cell size can be reduced from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /2 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /8 caused by the slow-wave effect of interdigital capacitance loaded at the end of the transmission line in the unit cell structure. Moreover, the capacitance loaded at the end of the transmission line can control the second and the third resonance frequencies to resonate as required. The unit cell has been designed at the fundamental frequency of 1.8 GHz and the controlled second and third resonance frequencies of 3.7 GHz and 5.2 GHz, respectively. The operating frequencies of the proposed FSS unit cell cover LTE band (0-1.9 GHz), Wi-MAX band (3.22GHz-4.7GHz), and WLAN band (5.15 GHz-5.95 GHz). The size of the unit cell is very compact which is 11.53 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times10.77$ </tex-math></inline-formula> mm. The designed unit cells are then connected as an array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> , resulting in an overall size of 92.31 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times86.16$ </tex-math></inline-formula> mm. This array has been used as a director for dipole antennas designed at the frequencies of 1.8 GHz, 2.45 GHz, 3.7 GHz, and 5.2 GHz. From the simulation, the dipole antennas with the proposed FSS director have directional gains of 4.52 dB at 1.8 GHz, 3.83 dB at 3.7 GHz, and 3.29 dB at 5.2 GHz, respectively. Measurement results show the directional gains of 3.67 dB at 1.8 GHz, 3.16 at 3.7 GHz, and 3.42 dB at 5.2 GHz, respectively. The proposed FSS director has properties of multi-band operation with a compact size that can be developed for antenna covers and radomes of multi-band wireless communications.

Tri-Band, Stable and Compact Patch Frequency Selective Surface Optimized via Hybrid Bioinspired Computing for Applications at 2.4, 3.5 and 5.8 GHz

This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioinspired computing and a general regression neural network (GRNN). This hybrid computational method, which utilizes the multi-objective cuckoo search algorithm combined to a GRNN, determine the best physical dimensions of the FSS in order to achieve a multi-band filtering at the 2.4, 3.5 and 5.8 GHz spectrums. Therefore, the results are to be applied to aid the propagation of Wi-Fi, WLAN, WiMAX and future sub-6 GHz 5G systems. The resonant frequencies were measured and a -10 dB cutoff value has been considered for the transmission coefficient. The triple rectangular loop conductor geometry of the device is printed upon a glass epoxy (FR-4) substrate. Measurements were made for different wave incidence angles, from 0° up to 45°, to demonstrate how signal incidence would affect the device’s functioning. The agreement between simulated and measured data display satisfactory results.

Synthesis of Multiband Frequency Selective Surfaces Using Machine Learning With the Decision Tree Algorithm

This paper presents the synthesis of multiband frequency selective surfaces (FSSs) using supervised machine learning (ML) with the decision tree (DT) algorithm. The proposed FSS structure is composed of an array of metallic patches printed on a dielectric substrate for stopband spatial filtering microwave applications. The shapes of the metallic patches are based on the sunflower (helianthus annus) geometry. In the first step, a parametric analysis is performed to investigate the use of different FSS geometries, including those with circular, annular and corolla integrated patch elements, to compose the sunflower geometry, regarding multiband and polarization independent performances with size reduction. Two bioinspired FSS geometries are synthesized using supervised machine learning with the decision tree algorithm. The random forest (RF) algorithm is used to validate the decision tree algorithm and to confirm the obtained results. The numerical analysis of the proposed FSS geometries is performed using Ansoft Designer software. Prototypes are fabricated and measured. The good agreement observed between simulated and measured results has validated the proposed approach. The use of supervised machine learning with the decision tree algorithm resulted in a particularly efficient and accurate synthesis procedure due to its intuitive implementation and simplified and effective data analysis modelling.

Design and analysis of angular stable antipodal F‐type frequency selective surface with multi‐band characteristics

This article presents frequency selective surface (FSS) with multi-band characteristics that features tri band band-stop and dual-band passband filter. The proposed FSS unit cell comprises the F-type resonance elements disposed of antipodal (diametrically opposed to) one to another on both layer and a square loop surrounding all resonators on the top layer of the dielectric substrate. The structure is specifically designed to filter out some extensively used broadband communication signals, such as, WiMAX and WLAN while enabling C-band satellite communication in the earth station and provides three stopbands operating at 2.4, 5.2, and 5.9 GHz besides two passbands of 4.1 and 5.5 GHz. Although this structure has a multi-band structure, it exhibits high stable performance for oblique incidence ranging from 0° to 60° for both transverse electric (TE) and transverse magnetic (TM) polarizations. Considering the resonant frequency deviation (RFD) at the incidence waves with different angles of arrivals, it was found that RFD at 60° is less than 0.6% on average and very low when compared with existing studies about multi-band FSS. The detailed equivalent-circuit model (ECM) is employed to predict and analyze the transmission characteristic of the proposed structure, and a good agreement between the simulated and measured transmission coefficients is obtained.

A Novel Fractal Multi-band Frequency Selective Surface

Abstract In this paper, a new multiband fractal frequency selective surface (MF-FSS) is proposed. The work presents a new fractal design methodology for FSSs with Swastika fractal patch elements. The proposed MF-FSS includes periodic arrays of metallic patches, printed on a single layer substrate. The structure parametric analysis is carried out in terms of fractal iterations, geometry elements, and unit-cell size. The simple controllable feature of the proposed structure lets us tune the given parameters of FSS geometry to achieve adjustable bandstop filter. The fractal geometry allows us to design compact structures (CP = 54%) that behave like dual-polarized bandstop filters. The designed structure is validated by means of an excellent agreement between the simulation and measurement results. Also, results show the proposed structure presents the most desirable features like fractal compactness, multiband response, dual polarization, excellent angular stability, and controllability. This work presents a fundamental structure that can be applied into the more complex and sophisticated designs in future.

Terahertz frequency selective surface based on metal‐graphene structure with independent frequency tuneability

This study proposes a set of tuneable terahertz (THz) frequency selective surfaces (FSSs) based on the metal-graphene structure. By the numerical technique, the transmission characteristics of the proposed FSSs are investigated in detail. In particular, the independent frequency tuneability of the proposed multiband FSS is demonstrated, i.e. the resonant frequency of each band can be tuned independently without affecting other bands. Such flexibility makes the proposed FSSs practical and potential for various THz applications including filters, radomes, polarisers, and sensors.

Single layer miniaturized ultra-thin FSS with five closely spaced bands

AbstractThis Paper reveals a novel single layer five band frequency selective surface (FSS). Novelties of the proposed FSS lie in its five closely spaced stop bands at 2.4, 3.38, 4.82, 6.32, and 7.75 GHz as well as the reduced single layer structural thickness (0.0016 λ0) and the miniaturized unit cell size (0.0656 λ0) at lower resonant frequency as compared to the existing multiband FSS. The unit cell structure consists of six octagonal concentric interconnected loops. Adjacent loop interconnection technique reduces the cell size by more than 44%. Furthermore, arrow-shaped rings are also introduced on each corner of the outermost octagonal loop, and using this technique approximate 23% cell miniaturization can be achieved. In addition, the proposed FSS exhibits excellent angular stability.

A Triple-Band Absorber With Wide Absorption Bandwidths Using an Impedance Matching Theory

This letter presents multiband absorbers with wide absorption bandwidths based on an impedance matching theory. A wideband absorber with a good absorption performance is served as a matching load for multiband bandpass frequency selective surface (FSS) filters. As a result, the reflection coefficients of the proposed absorbers are in high accordance with the counterparts of the original bandpass FSS filters. For demonstration, a triple-band absorber with wide absorption bandwidths is designed and fabricated by cascading a triple-band bandpass FSS filter and a wideband absorber together. The simulated results reveal that the proposed absorber has wide fractional bandwidths of 5.2%, 8.0%, and 6.4%, which is experimentally validated by the measured results.

Analysis of Finite Size Nonuniform Stable and Multiband FSS Using a Generalization of the WCIP Method

A generalization of the wave concept iterative procedure method is proposed and used in the analysis of finite size and nonuniform frequency selective surfaces (FSS). The nonuniformity of the FSS is obtained by mixing different shapes of elements in the finite size FSS structures consisting of circular patch elements with and without radial slits. The shapes of the radial slit elements are defined according to a fractal-like formation rule, where the circular patch without radial slits is the generator. Single or multiband frequency performances can be obtained, enabling the design of reconfigurable FSS. In addition, a high stability of the incidence angle of the plane wave is confirmed. A good consistency is observed among theoretical, simulation, and experimental results.

Multiband FSS Analysis and Synthesis Based on Parallel Non Coupled Metallic Strips Using WCIP Method

A novel parallel coupled Metallic strips frequency selective surface (FSS) is presented. The design is based on a filter composed of horizontal and vertical metallic strips. The structure has the advantage of simplicity and gives multi resonant frequencies easily controlled by a simple variation in the strips length. The proposed FSS rejects frequencies at 7GHz, 9.4GHz with bandwidths of 0.646GHz, 0.793GHz respectively when the structure is excited with an x polarized plane wave, and two frequencies at 9.1GHz and 11.2 GHz with bandwidth of 280.3MHz, 63MHz respectively when the structure is excited with a y polarized plane wave. To suppress frequencies ideal diode on reverse bias are inserted. The simulated results obtained using WCIP (Wave Concept Iterative Method) are compared to the COMSOL Multiphysics 4.3b software results, and measurements, a good agreement is observed. Then, an FSS synthesis approach based on non coupled parallel metallic strips is presented. It allows the synthesis of FSS for resonant frequencies ranging from 4.5GHz and 12.25 GHz for strips lengths inversely varying from 5mm to 19mm. To validate the synthesis approach, measured resonant frequencies are used as desired resonant frequencies to determine the metallic strips lengths. As a result the metallic strips FSS dimensions are extracted. Then the WCIP method is used to characterize the synthesized FSS. Three FSSs are synthesized based on the fabricated FSS and good agreement between measurements and synthesized FSSs results is recorded.

Multiband FSS with Fractal Characteristic Based on Jerusalem Cross Geometry

This paper proposes a new device with modifications on the Jerusalem Cross (JC) geometry to provide a multiband Frequency Selective Surface (FSS). Fractal iterations are created by introducing concentric self-similar JC copies in the original unit cell. This modification results in new dipoles at the structure which allows for the appearance of new bands proportional to these diploles' lengths, while maintaining total unit cell size. Four iterations of the JC FSS are studied in this paper. Simulation results for the insertion loss (S 21 ), surface current distribution and measurement results are presented.

Tunable THz Multiband Frequency-Selective Surface Based on Hybrid Metal–Graphene Structures

In this letter, a tunable multiband THz frequency-selective surface (FSS) is developed based on hybrid metal–graphene structures. The tunability characteristics are realized by inserting graphene strips between metal patches. The proposed FSS is studied based on the equivalent circuit model, which is validated against the simulation results using numerical methods. It is shown that the proposed hybrid structure has good performance in terms of bandwidth, gain, and tunability, and it is easy to be built as a potential competitor for THz applications.