Single-layer Frequency Selective Surface Research Articles

Tunable liquid crystal double-layer frequency selective surface with wide transmission band and small insertion loss

ABSTRACT In this paper, a tunable Frequency Selective Surface (FSS) based on liquid crystal (LC) with a wide transmission band, large tuning range, high tuning rate, and miniaturization is designed. First, a single-layer FSS is developed with two frequency selective layers and one LC tunable layer. The simulation and experiment results show that the single-layer FSS has a transmission bandwidth greater than 4.25 GHz, and the LC change can make the center frequency of the transmitted band shift to the lower frequency by 576 MHz, with a tuning rate of 4.2%. Subsequently, a double-layer FSS is designed by adding a coupling layer to the single-layer FSS, achieving a flat-top passband and enhancing the tuning rate. Simulation and experimental validation show that altering the LC state enables continuous tuning of the center frequency of the double-layer FSS from 14.95 GHz to 13.86 GHz, with a tuning rate of 7.2%. This structure exhibits a flat-top passband wider than 5.7 GHz, a relative bandwidth of 41%, and a rectangular coefficient below 1.877. Moreover, the double-layer FSS demonstrates favorable polarization stabilization and wide incidence angle stabilisation properties in various states.

Enhanced Gain Dual-Port Compact Printed Meandered Log-Periodic Monopole Array Antenna Design with Octagonal-Ring Shaped FSS for Broadband 28 GHz Applications

AbstractIn this article, we propose a microstrip-fed printed meandered log-periodic monopole array (PMLPMA), and its dual-port configuration incorporating an octagonal ring frequency selective surface (FSS) layer. The dual-port PMLPMA antenna system has a compact structure with a total dimension of 18.75 × 18.75 mm2 and is designed to operate in the 5G n257 (28 GHz) band. The proposed PMLPMA radiator consists of five log-periodic monopole array elements, and the dual-port antenna system comprises two identical PMLPMAs placed vertically next to each other. Additionally, an octagonal ring-shaped single-layer FSS was implemented on the proposed antenna system to increase the gain across the operational band. Simulation results demonstrate that the dual-port PMLPMA antenna achieves a peak gain of about 3.5 dBi without the FSS layer, while a peak gain of 7.35 dBi is achieved when the FSS layer is augmented on the antenna. Moreover, isolation levels exceeding 30 dB are obtained for both cases between the 26.5–29.5 GHz frequency ranges. To verify the simulation results, the dual-port PMLPMA antenna system, and the octagonal ring-shaped FSS layer are also prototyped. The measurements align closely with the simulations in terms of performance criteria such as gain, bandwidth, and radiation patterns. Thus, the 28 GHz band antenna system exhibits great potential for 5G mobile applications.

Single-Layer Frequency-Selective Surface on Window Glass for 5G Indoor Communications

Single-Layer Frequency-Selective Surface on Window Glass for 5G Indoor Communications

Performance enhancement of Vivaldi-shaped planar UWB antenna using a single-layer FSS reflector

This work proposes the design of a frequency-selective surface (FSS)-based planar monopole antenna for ultra-wideband (UWB) communication applications. The UWB response is observed by integrating a Vivaldi-shaped slot and by introducing a stepped-like pattern on the bottom edges of the radiating patch, while the back side is composed of a partial ground plane. This configuration results in a broad impedance bandwidth spanning from 3.11 to 20 GHz. For radiation performance enhancement of the proposed antenna, a single-layer UWB FSS reflector is placed beneath the antenna element at an optimized distance. The proposed FSS reflector employs a 3 × 3 array of fractal structure with a unit cell size of 12.25 × 12.25 mm2. The designed FSS reflector exhibits a linear phase response over a frequency range of 3.28 to 14 GHz, with a stop-band transmission coefficient less than -10 dB. The incorporation of the FSS reflector results in an increased gain, elevating it from 1 to 4 dBi at low-band frequencies, while at mid-band frequencies, the gain is increased from 1 to 6 dBi. The structural configuration of the proposed antenna yields directional far-field patterns, making it well-suited for UWB radar applications.

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

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

Design of Wideband Two-Sided Bandpass Frequency Selective Surface for X, Ka, and Ku Band Application

A novel wideband bandpass frequency-selective surface functioning at X, Ku, and Ka bands is proposed in this article. The designed FSS has a metallic square loop and a circular ring, and they are printed on both sides of the FR4 substrate. The proposed design FR4-based single-layer FSS is operating from 11.075 GHz to 22.075 GHz with a fractional bandwidth of 66.36%. The parameters of the square loop and circular ring regulate the characteristics of the passband. The optimum dimension of these parameters is obtained with parametric analysis. The proposed structure is measured and fabricated. However, the measured results strongly agree with the simulated results, which authenticate the proposed design performance.

Targeted Design of Single-Layer Frequency-Selective Surface With Angular Stability Based on Topology Optimization

Targeted Design of Single-Layer Frequency-Selective Surface With Angular Stability Based on Topology Optimization

A configuration to double the gain of pyramidal horn antenna using single layer frequency selective surface

AbstractA gain enhancement technique in pyramidal horn antenna using a slot type band pass frequency selective surface (FSS) is presented. The horn antenna without FSS has achieved a measured gain of 10.5 dBi at 10 GHz, while the antenna with the single layer slotted FSS yields an enhanced measured gain of 14.2 dBi (an improvement of 3.7 dB or 134%). Conventionally, such a gain enhancement would 5 times increase in its dimensions (flaring). However, the authors achieve the same with only 2 times increase in dimensions. Another interesting value addition of the proposed idea is that an FSS sheet can be added to the existing horn antenna to increase its gain without altering the antenna itself. Such a scheme is highly beneficial in strategic applications. The proposed gain enhanced horn antenna can be recommended to be utilised in several X‐band applications, such as radar systems (weather, surveillance, traffic control and military), satellite communications and point–point microwave links that require high gain and small form factor.

An Angle-Stable Ultra-Wideband Single-Layer Frequency Selective Surface Absorber

An ultra-wideband polarization-insensitive frequency selective surface (FSS) absorber is proposed for S to K-band applications. The absorber comprises two compensation slabs, a lossy FSS layer and a grounded dielectric plate. The FSS unit cell is a combination of a second-order Chinese knot and a cross. To enhance the bandwidth and angular stability of the single-layer FSS absorber, a compensation layer composed of FR4 and polymethyl methacrylate (PMMA) slabs is incorporated. The proposed FSS absorber demonstrates a remarkable absorption rate of over 90% within the frequency range of 3.1–22.1 GHz, exhibiting a fractional bandwidth of 150.8%. Even when subjected to an oblique incidence of 45°, the absorber maintains an 80% absorption rate in the frequency range of 4.4–19.1 GHz for both TE and TM polarizations. The total thickness of the FSS absorber is 0.0848 λL (the wavelength at the lowest cutoff frequency), and only 1.08 times the Rozanov limit. To validate the design, a prototype of the proposed absorber was fabricated and measured. Good agreements were observed between the simulations and measurements.

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.

Design of Broadband High-Gain Fabry-Pérot Antenna Using Frequency-Selective Surface.

In this paper, a broadband high-gain Fabry-Pérot (F-P) antenna composed of the air-loaded slot-coupled broadband microstrip antenna and the frequency selective surface (FSS) based positive gradient reflection phase structure is proposed. Taking advantage of the superposition effect of multiple reflections and transmissions occurring between layer structures, the gain enhancement was realized. Meanwhile, by cascading the single-layer FSS and the dielectric substrate, the positive gradient reflection phase over a wider frequency range was achieved. Simulated results show that the resonant frequency of the designed F-P antenna is 10 GHz, the impedance matching band (S11 < -10 dB) ranges from 8.3 GHz to 11.25 GHz with a bandwidth of 29.5%, and the antenna gain is improved significantly in the range of 8.1 GHz~11.25 GHz with a gain bandwidth of 31.5%. For further verification, a prototype was fabricated, and the experimental and simulated results are in good agreement.

Design of a Compact Single-Layer Frequency Selective Surface With High Oblique Stability

In this article, a compact single layer band stop frequency selective surface (FSS) with superior resonant stability is presented. The proposed FSS unit comprises of a symmetrically modified square loop. The square loop has been modified in order to increase the perimeter. Moreover, modified square loop is arranged in C4 rotational symmetry to ensure the polarization independence. The designed FSS exhibits highly stable response for the incident angle variation from 0° to 86°. At the resonant frequency of 5.54 GHz, its miniaturized unit cell size is 0.09 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> × 0.09 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> and the thickness is only 0.007 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> . The operating phenomenon of this FSS is explicated by analyzing the equivalent circuit model, electric field and surface current distributions at resonant frequency. A test sample of the designed FSS has been constructed for the validation purpose. The transmission coefficients response of the proposed FSS has been measured and found to be congruent with the simulated responses. The salient features that distinguish the proposed FSS design over others are low complexity, low thickness, compact unit cell and excellent angular stability.

A dual‐polarized wideband gain enhancement Fabry–Perot antenna by adopting a wedge‐shaped phase correcting structure

A dual-polarized wideband Fabry-Perot (FP) antenna based on a wedge-shaped phase correcting structure (WPCS) is proposed. The antenna adopts a wideband dual-linear polarized slot-coupled antenna as a primary antenna, and adopts a single-layer FSS structure with positive reflection phase gradient characteristics as a partially reflecting surface (PRS) of the FP resonator, to optimally excite the FP cavity resonances within a wide operating band. Moreover, a small circular metal patch array is printed on the other side of the FSS unit structure. The small circular patch array effectively increases the reflection amplitude without changing the positive reflection phase gradient characteristics of the PRS, which improves the FP antenna gain. In addition, a highly graded WPCS is loaded in the resonant cavity to properly compensate the phase between different reflection paths inside the resonant cavity, which enhances the gain of the FP antenna in a wide band. Finally, the measured peak gains of the FP antenna under the excitation of Port 1 and Port 2 are 16.0 dBi and 15.89 dBi, respectively, and the gain enhancement can reach up to 3 dBi after loading the WPCS. The measured 10-dB impedance-matching operating bandwidth of dual-polarized common coverage is 14.08 to 16.45 GHz (15.53%).

Electromagnetic Characteristics Calculation of FSS by the Mixed Method FDTD/Extrapolation/Cascade Method

In this paper, a mixed method (MM) combining the advantages of finite difference time domain (FDTD), extrapolation, and matrix cascade methods is proposed. First, the hybrid algorithm combining the FDTD and extrapolation method is used to compute the electromagnetic characteristics of the single-layer frequency selective surface (FSS). Subsequently, matrix cascade method is used to calculate the electromagnetic characteristics of the multi-layer FSS. By introducing the Floquet theorem and considering the periodic boundary condition (PBC), absorbing boundary conditions (ABC) of the FSS, a three-dimensional model, is established. The computational results show that, while maintaining the same level of accuracy, the hybrid method greatly improves the computation speed and reduces the computer memory compared with the simulation software. It can provide an important reference for the subsequent study of the electromagnetic characteristics ofthe FSS.

A broadband Fabry–Perot resonator antenna using partially reflecting surface with positive reflection phase gradient

A novel Fabry–Perot resonator antenna with a wide impedance- and gain-bandwidth is proposed in this paper. A wideband aperture-coupled microstrip antenna is used as the primary source, and a single-layer frequency selective surface with a positive reflection phase gradient is designed as a partially reflective surface. To validate the proposed approach, a prototype antenna operating in the X-band is designed, fabricated, and measured. Both simulation and measured results indicate that the proposed antenna exhibits wideband characteristics. The measured impedance bandwidth (|S11| &amp;lt; −10 dB) is 64.4%, ranging from 8.68 to 15.12 GHz. The experiments demonstrate that a 3 dB gain bandwidth of 31.9% from 8.61 to 11.80 GHz with a peak gain of 14.0 dBi at 10 GHz is achieved. In addition, the proposed antenna reveals good directional radiation patterns, low side-lobe level, and low cross-polarization over the whole working band.

An FSS Based Broadband Elliptical Tree Shaped Antenna with Augmented Gain for Wireless Applications

This research presents a coplanar waveguide fed elliptical-based second iterative antenna for dual-broadband applications. The antenna radiator is formed after implementing two iterations of an elliptical-shaped patch in a tree-shaped manner and a modified semi-elliptical CPW plane. The antenna provides a bandwidth of 1.87 GHz (2.49–4.36 GHz) in the lower resonating band and 1.96 GHz (7.96–9.92 GHz) in the upper resonating band with peak gains of 2.84 and 6.15 dBi, respectively. An augmented gain of 9.48 dBi is obtained by implementing a single-layer FSS (frequency selective surface) beneath the designed antenna. The simulated and experimental results of the antenna with and without FSS are very similar regarding gain, impedance bandwidth, and directional radiation patterns. The antenna described in this article is simple, inexpensive, and low profile in nature. It can be used for Wi-MAX, lower sub-6 GHz 5G (n78), and x-band applications.

Wideband and High Gain Array Antenna for 5G Smart Phone Applications Using Frequency Selective Surface

This work presents an eight element array antenna with single layer frequency selective surface (FSS) to obtain high gain. The eight elements are fed by single port. The FSS consists of 14x6 unit cells with one unit cell size is 5&#x00D7;5 <i>mm</i>² having wideband behavior. The antenna uses Rogers RT Duroid 5880 substrate and giving very wide bandwidth from 20 GHz to 65 GHz, covering mm-wave 5G bands (including 28 GHz, 38 GHz and 60 GHz). The designed FSS is showing stop band transmission characteristics below -10 dB threshold from 25 GHz to 42 GHz and 59 GHz to 61 GHz. The eight element antenna integrated with the FSS reflector, which results an improvement in the gain level from 12 dB to 15 dB at 28 GHz, from 10 dB to 12 dB at 38 GHz, and from 9.5 to 11 dB at 60 GHz. The dimensions of the antenna are 33&#x00D7;27&#x00D7;0.787 <i>mm</i>³. The proposed antenna shows stable gain and directional radiation patterns. The simulation findings are experimentally confirmed, by testing the fabricated prototypes of the proposed antenna system.

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.

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

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