Type Frequency Selective Surface Research Articles

Infrared camouflage and radar compatible stealth structure based on metamaterial

In this study, an infrared camouflage and radar compatible stealth structure based on metamaterial is designed and fabricated. Two types of frequency selective surfaces (FSS) with different infrared emissivity values are arranged into a specific pattern, which is similar to a visible camouflage pattern. The different infrared emissivity regions in the infrared camouflage layer (IRCL) are 0.27, 0.55, and 0.93, and the radar waves transmittance within 18 GHz is greater than 98%. Below the IRCL is a wideband radar metamaterial absorber based on square-ring resonant elements, which can absorb the radar waves and dissipate them through ohmic loss. The particle swarm optimization algorithm combined with the equivalent circuit model rapidly optimises the structure of the radar metamaterial abosrber, achieving an absorption rate greater than 90% from 4.5 GHz-18 GHz. And the absorption efficiency still maintains 80% at an oblique incidence range of 45°. The Indium Tin Oxide (ITO) film was etched by laser to obtain the above microstructures. The combination of two layers of metamaterial structure realizes the compatible stealth capability of infrared camouflage and radar absorption.

Bandwidth control of loop type frequency selective surfaces using dual elements in various arrangements

Frequency selective surfaces (FSSs) have applications across multiple disciplines due to their unique electromagnetic properties. This paper investigates the use of both rounded square loops, and simple loop type dual elements arranged in unique patterns, to control the transmission and reflection bandwidth and resonant frequencies over KU and K frequency bands supported by equivalent circuit models. The FSSs were fabricated using laser engraving to create conductive loop type elements on a thin, flexible and optically transparent Mylar substrate (relative permittivity of 2.7 and thickness of 65 μm). The frequency response of the surfaces are controlled through the element self-inductance and capacitive coupling with neighbouring elements. This work shows that different arrangements result in the formation of multiple distinct resonances. The theoretical and experimental results were in good agreement where rounded squares and dual element arrays were employed to create broadband and multiband band-stop FSSs. A polarization sensitive surface exhibited stop-bands at 12 and 16 GHz in transverse electric polarization and a stop-band at 14.4 GHz in transverse magnetic polarization. This technique can be applied to any periodic array through careful selection of the individual elements in the array, as well as their arrangement.

Broadband RCS reduction for both microstrip array and Fabry‐Perot antenna based on the quasi‐ AMC superstrate

This article presents a new type of quasi-AMC superstrate (QAMCS), which can achieve wideband RCS reduction (RCSR) for both the microstrip array and Fabry-Perot (FP) antenna. The proposed QAMCS comprises of two-layer metallic patterns with a thin air gap. The top-layer consists of two types of frequency selective surfaces (FSSs) in a checkerboard layout, and the wideband RCSR is realized based on the phase cancelation principle. The bottom-layer consists of the slotted FSS, to reflect out-of-band signal while allowing the in-band signal to pass through with a low insertion loss. Besides, the reflection phase of the proposed QAMCS is about −180° around higher frequencies. Therefore, it can be regarded as a partially reflecting surface (PRS) to construct the FP antenna with a highgain and low-RCS. The simulation and measurement results show that the bandwidth of 10-dB RCSR is more than 76% (7.2-16.1 GHz). The 10-dB impedance bandwidth of the array antenna is ranging from 16.6 to 18.6 GHz. For the FP antenna, its aperture efficiency is 31.5% and the peak gain is 17.5 dBi at 20 GHz.

Gain Enhancement of CPW Antenna for IoT Applications using FSS with Miniaturize Unit Cell

Wireless connectivity is a critical enabler for many IoT applications. Antennas are often required to be installed inside the device cover, which usually occurs in small sizes with optimal performance. On the other hand, a suitable antenna should also have high efficiency, gain and adequate bandwidth covering the desired frequency range. Here, we proposed new type of Frequency Selective Surface (FSS) with miniaturized resonator element to enhance the gain of an CPW antenna. Furthermore, the miniaturization of the Frequency Selective Surface unit cell is attained by coupling the two meandered wire resonators. The wire resonator is separated by thin and single substrate layer. The structure of the FSS is shown to have a FSS unit cell dimension that is miniaturized to 0.057λ. The CPW antenna size is only 28.8mm × 46.5mm operating at 2.45 GHz frequency. With the additional of the FSS, the antenna’s gain reaches up from 1.8 dBi to 2.6 dBi with omnidirectional radiation pattern.

Wide-Angle Broadband Rasorber for Switchable and Conformal Application

A novel wide-angle and broadband rasorber is presented incorporating several advances. To broaden the bandwidth, we introduce a new type of frequency selective surface (FSS) in the bottom layer of the rasorber. This strategy increases the upper and lower absorption bandwidths while reducing the insertion loss at transmission window. Furthermore, a new top resistive layer is proposed via the loading of electric field coupled resonator elements on a cross-dipole structure. The proposed design offers both, an angularly stable performance and a thin structure that can be fabricated on a single dielectric substrate. To enable switchability, p-i-n diodes are employed and a reconfigurable rasorber/absorber is designed where a new concept of “lossy/lossless” top layer is investigated and established as the best choice among other switchable designs. Equivalent circuit models are constructed for both active and passive designs to provide physical insight into their operation. Finally, to enable deployment of the rasorber over curved geometries, these advances are incorporated into a conformal structure. Three separate prototypes are fabricated and good agreement is obtained between design predictions and experimental results.

A Large Angle Stability Frequency Selective Surface

In order to solve the problem that the stability of general frequency selective surface (FSS) is bad when the electromagnetic wave is irradiated by large incident angle, a tripole type FSS structure with large angle stability is designed. The frequency response characteristics of the FSS for different incident angles are simulated. The results show that the novel structure has good stability of large angle in X band. It has good practical value in the fields of curved radome.

Sharp Triple-Notched Ultra Wideband Antenna with Gain Augmentation Using FSS for Ground Penetrating Radar

A printed ultra-wideband antenna that provides wide bandwidth of 2.6–10.58 GHz, with sharp triple notches at 3.3–3.92, 5.1–5.4 and 5.68–6.02 GHz to eliminate the WiMAX and WLAN interferences, is proposed. Triple notches are implemented by embedding split ring shaped slot and unique circular split ring resonator pairs in the antenna. The antenna provides monopole like radiation patterns with gain variation of 2.5–5 dBi and average radiation efficiency of 86% in its pass band. Wide bandwidth of the antenna makes it well suited in low depth subsurface scanning ground penetrating radar (GPR) applications where better lateral resolution is desired. To improve the depth resolution, the antenna is integrated with reflective type frequency selective surfaces. Overall gain augmentation of 3 dBi with maximum gain increment of nearly 6 dBi at 5.5 GHz is achieved by adding the FSS. The antenna-FSS composite structure provides impedance band of 2.52–10.66 GHz with triple notches at 3.26–3.84, 5.1–5.38 and 5.66–5.95 GHz. Performance of the composite structure is evaluated in close proximity of sandy soil test bed by keeping thin aluminium sheet at the bottom of sand. Adequate VSWR, transfer function and group delay responses ensure the eligibility of proposed antenna to work for GPR.

Tripole type wideband bandpass frequency selective surface for X‐band applications

The study presents a novel single dielectric layer wideband bandpass frequency selective surface (FSS) topology. The structure is designed using a kind of the tripole type FSS which has been analysed for its behaviour. Next, the operating bandwidth has been increased by using the meander lines in the middle of the unit-cell. The proposed FSS structure covers the X-band (45.03% fractional bandwidth) of the electromagnetic (EM) spectrum with a −3 dB transmission bandwidth. Its −1 dB bandwidth extends from 7.93 to 11.93 GHz. The wide operating bandwidth with a single dielectric layered structure makes it suitable for the hybrid radome applications. For the normally incident EM wave, adjacent to the lower and upper cut-off frequencies, the structure offers better than 18 dB attenuation which increases the out of the band rejection. Finally, the proposed structure is fabricated and experimentally verified for the dual polarisation and angle stability up to 45°. Eventually, to prove the novelty in terms of the operating bandwidth and the fabrication simplicity, an exhaustive state-of-the-art comparison is also presented.

Water-Based Reconfigurable Frequency Selective Rasorber With Thermally Tunable Absorption Band

In this paper, a novel water-based reconfigurable frequency selective rasorber (FSR) at microwave band is proposed, which has a thermally tunable absorption band above the transmission band. The water-based FSR consists of a bandpass type frequency selective surface (FSS) and a 3D printing container. The water substrate is filled into the sealed space constructed by the above two structures. The numerical simulation results show that the FSR can achieve absorption with high absorptivity from 8.3 to 15.2 GHz, and obtain a transmission band of 5.2 to 7.0 GHz. The minimum insertion loss of the transmission band reaches 0.72 dB at 6.14 GHz. In addition, the FSR has the reconfigurable characteristics of absorbing or reflecting electromagnetic waves by filling with water or not. The proposed water-based FSR shows its good transmission/absorption performance under different polarizations and oblique incident angles. Due to the Debye model of water, the absorption band can be adjusted by water temperature, while the passband remains stable. At last, prototype of the FSR based on water has been fabricated, and the experimental results are presented to demonstrate the validity of the proposed structure.

Compact ultra‐wideband antenna: improvement of gain and FBR across the entire bandwidth using FSS

In this paper, a highly compact ultra-wideband (UWB) monopole antenna with high gain is proposed. The UWB monopole antenna consists of U-shaped radiating patch. The ground plane comprises of edge-truncated partial rectangular metallic plane with a rectangular slot at the centre of the top edge. The proposed antenna having a very compact dimension of 16 mm × 22 mm × 1.6 mm is compatible and highly suitable for compact wireless systems. Further for enhancement of directivity of the UWB antenna, a patch type frequency selective surface (FSS) is placed below the antenna. The combined FSS-antenna structure operates with high gain (peak gain of 9.4 dBi) across the entire UWB range (3.1-18.6 GHz). The proposed design also offers an appreciably high front-to-back lobe ratio of ~10 dB across the entire UWB range. The simulated results are verified experimentally and the results are discussed in detail. The overall dimension of the proposed FSS integrated composite antenna is 52 mm × 62.5 mm × 23.2 mm, which is highly relevant for high-gain applications.

Chipless frequency selective rasorber with stable performance for oblique incidence

This Letter presents the design of a frequency-selective rasorber that selectively absorbs undesired (out-of-band) signals and selectively transmits desired (in-band) signals by using planar resistor technology without lumped elements. To implement the selective absorption characteristic on the upper surface, a lossy layer was implemented in the proposed structure by using a nickel-phosphorus metal alloy-based resistor–conductor material. Furthermore, stable transmissive/absorptive performance against polarisation and incidence angle was implemented by laminating a quarter-wavelength thickness of dielectric spacer and bandpass type frequency selective surface together. The resulting design was verified through experimental measurements.

Design and analysis of a tri-band frequency selective surface with a second-order response

AbstractIn this paper, a sandwiched type frequency selective surface (FSS) is designed and analyzed. The design procedure and operating principle is given based on the equivalent circuit model. The proposed FSS includes two identical layers of periodic metallic arrays, which are separated by a foam layer. In each layer of the periodic array, the unit cell is composed of a gridded-triple square loop structure. The FSS provides three pass-bands, in which a flat band response is presented. Three bands are separated by one or two transmission zeros, which leads to a sharp rejection on both sides of each pass-band. The central frequencies of the three pass-bands are 7.0, 10.9 and 14.0 GHz. To verify the simulated results, a prototype of the FSS is fabricated and measured. The simulated results agree well with the measured ones. This work can be used in area of a radar stealth or satellite communication system.

Frequency selective surfaces on flexible thin plastic substrates

The capability of the flexible substrate of the frequency selective surface (FSS) to filter out particular frequency is discussed in this paper. A new type of FSS are applied using flexible thin plastic substrate to enhance the performance of the conventional FSS that lacks of flexibility and cannot be used in bending surface. A simulation based investigation shows that the diameter or length of the square has a significant effect on the band-stop selective characteristic of the FSS. The frequency response of the band-stop are at 2.45GHz that drop at -10dB.

FSS on energy saving glass for rf communication enhancement in modern building

<span>The use of energy saving glass has become very popular in the modern day building design. This energy saving property is achieved by applying a very thin tin oxide (SnO2) coating on one side of the glass. This coating can provide good thermal insulation to the buildings by blocking infrared rays while being transparent to visible part of the spectrum. Drawbacks of these energy saving windows is that it also attenuates the transmission of useful microwave signals through them. These signals fall within the frequency band of 0.8GHz to 2.2GHz. In order to pass these signals through the coated glass, the use of aperture type frequency selective surface (FSS) has being proposed. In the present work, SnO2 thin film with FSS structure was fabricated. Microwave transmission through SnO2 coated glass with FSS structure was also analyzed using network analyzer. The result of computer simulation was confirmed and consistent with the network analyzer results that showed the improvement of SnO2 coated glass with the FSS structure.</span>

Ultrawide Bandwidth Electromagnetic Wave Absorbers Composed of Double-Layer Frequency Selective Surfaces with Different Patterns

A novel design for an ultra-wide bandwidth and thin microwave absorber is introduced utilizing two frequency selective surfaces (FSSs) with different patterns of resonating frequencies. The circuit parameters, inductance and capacitance, of the three types of FSS (square loop, cross, square patch) were determined using an equivalent circuit and strip wire conductor model. The square loop FSS indicates a low frequency resonance (10 GHz) due to its high inductance and capacitance. On the other hand, the square patch of small inductance reveals a high resonating frequency (36 GHz). By optimizing the combination of the two FSSs, an ultra-wide absorption bandwidth (6.3–40.0 GHz for −10 dB reflection loss) was designed with a small total thickness of 5.5 mm, which is close to the theoretical limit. The free space measurement result with a test sample prepared by the screen printing method was in good agreement with the simulation result and verified the validity of the proposed design method. For these periodic array structures, however, the grating lobes were observed above the high frequency limit, and it needs to be emphasized that the further control of the unit cell periodicity is important, particularly for large oblique incidence angles.

Rapid and high-performance processing technology for large-area frequency selective surfaces

Frequency selective surfaces (FSSs) with periodic smart structures have widespread applications in many areas, especially in electromagnetic wave filters. In this paper, a rapid and high-performance processing technology for large-area FSSs was presented. This novel technology combined laser direct writing lithography (LDWL) with wet chemical etching (WCE) (i.e., LDWL + WCE). Basing on experiments and in the condition of optimal parameters (i.e., 40 mW laser power, 1000 mm/s scan speed, single scan, 20 μm hatch space, pattern-profile scan path, and ferric chloride aqueous solution as etchant) of LDWL + WCE, a large-area (200 × 200 mm2) aperture type FSS with 625 square-loop units was fabricated within 8 min on a FR-4 copper-clad plate (with 12 μm-thickness copper layer). When the same FSS was prepared by commonly-used laser direct ablation (LDA) technology with itself optimal processing parameters, it needed about 62 min (nearly 8 times as much time as the former). Scanning electron microscopy (SEM) and surface probe profilometry analyses showed that the edges of the square-loop patterns fabricated by LDWL + WCE were steeper and smoother, and the FR-4 substrate had no damage. In an anechoic chamber, the electromagnetic wave filtering performances of the as-prepared FSSs were tested, and the results indicated that the FSS fabricated by LDWL + WCE had a bandpass response at 7.08 GHz with a transmittance of 97.75%. Its frequency response curve was in better agreement with the simulation result. The technology of LDWL + WCE also has the potential to rapidly fabricate large-area and/or non-planar FSSs with high performance.

140 GHz Frequency Selective Surface Based on Hexagon Substrate Integrated Waveguide Cavity Using Normal PCB Process

A frequency selective surface (FSS) based on hexagon substrate integrated waveguide (HSIW) technology is proposed in this letter and designed at the center frequency of 140 GHz. The periodic element comprises a HSIW cavity and two circular slots etched on the top and bottom conductor claddings of the cavity. Based on the hexagon cavity, this type of FSS has a better polarization stability and a closer element arrangement compared with square cavity FSS and circular cavity FSS, respectively. Besides, circular slots are better than polygonal slots which have round corners at their corners when fabricated using normal printed circuit board process. Thus, the HSIW FSS can achieve a good and stable performance at terahertz band. The proposed structure is fabricated and the measured result has a good agreement with the simulated one.

Multiband and Miniaturized dual layer Antenna incorporated with FSS and DGS

A novel dual layer rectangular printed Antenna based on loop type Frequency selective surfaces with five concentric rings and I shaped defected ground structure (DGS) is designed and investigated. The deigned antenna is tested for application in C band, WiFi devices and some cordless telephones and X band radiolocation, airborne and naval radars as multiband operational frequencies are at 5.5GHz, 6.81GHz, 9.3GHz and thus covers two wireless communication band C Band (4 to 8GHz ) and X band (8 to 12 GHz) The bandwidth is 200MHz, 300MHz and 1GHz respectively and measured gain of this designed antenna are 2.42dBi against 5.5GHz, 2.80dBi against 6.81GHz, 6.76dBi against 9.3GHz. The proposed antenna in addition to multiband operation also exhibits minituarization.The Floquet port technique is used to analyse concentric rings. The Results comparison of proposed structure with the basic dual layer antenna resonaing at 5.5GHz shows the patch area is reduced by 58.15% while the volume of the antenna is reduced by 81.5%.

Study of pass band resonance characteristics of aperture type FSS

In this paper, the resonance characteristics of aperture type frequency selective surface (FSS) is presented. A systematic investigation is carried out to design the compact FSS. The optimized structure consists of rectangular Archimedean spiral with inter-digital capacitance. Resonance characteristics is verified in both single-layer as well as the double-layer approach by embedding FSS on one side of the dielectric substrate. The performances of the dual-layer are observed by varying air-gap between two FSS layers. The structure offers satisfactory resonance (transmission and reflection) characteristics at optimum air-gap of 7 mm between two layers with the 3 dB cutoff region over a frequency range (3.66–4.66 GHz). Finally, an array of 31 × 31 FSS elements of two layers is fabricated for experimental characterization. A close agreement between simulated and measured results is observed.

Resonant characteristics of aperture type FSS and its application in directivity improvement of microstrip antenna

In this paper, we propose an aperture type frequency selective surface (FSS) by employing an array of 12×12 unit cell elements and its resonant characteristics is analyzed. A resonant cavity antenna is then formed by the ground plane substrate and the FSS superstrate. The high reflective behavior of the proposed FSS at an offset of the resonance is then utilized for improving the performance of this cavity antenna. The impedance bandwidth and directivity are improved up to 0.66GHz and 8.95dBi, simultaneously at an optimum gap of 17.6mm between the antenna substrate and FSS superstrate. For validation purpose, prototypes of both patch antenna and FSS, are fabricated and characterized. A fairly good agreement is achieved between the measured and simulated results.