Wideband Frequency Selective Surface Research Articles

Design of Wideband Frequency Selective Surface Based on the Combination of the Equivalent Circuit Model and Deep Learning

In this letter, a design method for frequency selective surface (FSS) based on the equivalent circuit model (ECM) and deep learning is proposed. In the proposed method, the ECM depicting the target transmission characteristic is first established. Then, with the aid of the established ECM, the target transmission characteristic is converted into the desired transmission curve and the initial topology of the FSS structure is determined. The cascade network is adopted to realize the rapid inverse design of the FSS structure. Benefiting from the established ECM, the high quality of the training data and proper description of the design target can be ensured in deep learning. For verification, an ultra-wideband FSS structure with a passband ranging from 3.1 to 12.05GHz and a stopband ranging from 12.85 to 20GHz is designed. Both simulated and experimental results show that the designed FSS provides an ultra-wide passband with flat-top and fast roll-off characteristics, covering 98.9% target passband and 95.3% target stopband.

Design of miniaturize flexible wideband frequency selective surface for electromagnetic shielding application

In this paper, a flexible, ultra-thin, miniaturized broadband frequency selective surface (FSS) is demonstrated for wideband electromagnetic shielding application. The unit cell of the proposed FSS structure consists of cross dipoles loaded with the metallic circular strip. The proposed miniaturized FSS structure has an extremely low profile with a thickness of and a unit cell size of . This FSS structure provides wideband shielding of more than 20 dB from 1.1 to 2.6 GHz frequency region. Besides this wide stopband, the FSS structure acts as a transparent window in the frequency band which can be used for the 5G communication purpose. Moreover, by comprehending the interaction between the incident electromagnetic wave and unit cell, a conceptual equivalent circuit model is developed that helps to interpret the mechanism of the miniaturization as well as the broadband response of FSS structure. We also compared the proposed FSS with other recently reported structures and observed more than 55% improvement in size reduction with several other miniaturized flexible FSS structure. Furthermore, this FSS structure exhibits 20 dB attenuation over a wide frequency region with a fractional bandwidth of 111%. Moreover, excellent resonant stability is achieved in regards to different polarization and incident angle up to .

Frequency-Selective Surface Stopband Designed with a Genetic Algorithm for Gain Enhancement of a Broadband Monopole Antenna

This paper presents an unusual, high-performance, cost-efficient, wideband frequency-selective surface (FSS) designed with a genetic algorithm (GA) and its effect on the performance of a broadband M-shaped monopole antenna. Each FSS unit cell with the dimensions of 0.2λ<sub>0</sub> × 0.2λ<sub>0</sub> × 0.01λ<sub>0</sub> acts as a stopband filter for a wide bandwidth of 5.5 GHz (105%, 2.6–8.1 GHz). The FSS properties and advantages to antennas were tested via numerical simulations and measurements, respectively. Using the 6×6 array of the designed FSS unit cell as a reflector, the antenna impedance bandwidth improved from 96.1% (3.1–8.1 GHz) to 98.07% (3.3–8.4 GHz), with a center frequency of 5.2 GHz. In addition, the antenna gain improved at the maximum of 7.8 dBi, which was sustained from 9 dBi to 10.1 dBi for the entire bandwidth.

A compact super wideband antenna with stable and improved radiation using super wideband frequency selective surface

A small bulb shaped planar super wideband (SWB) antenna with the dimension of 35 × 30 × 0.8 mm3 operating over 2.8–40 GHz (14.28:1) spectrum is proposed. The antenna offers a fractional bandwidth of 173.8%, bandwidth dimension ratio (BDR) of 1904, measured peak gain of 5.5 dBi and radiation efficiency of 80%. The proposed antenna is unified to an unique SWB frequency selective surface (FSS), having unit cell size equal to 0.114λL × 0.114λL × 0.008λL (λL is the wavelength at 3.1 GHz). The FSS operates in 3.05 to 35.92 GHz spectrum (168.7%) with transmission level S21 ≤ -10 dB and reflection S11 near 0 dB for TE and TM modes of polarization with adequate angular stability. The linearly decreasing S11 phase of FSS makes it appropriate for radiation improvement of the bulb shaped antenna in the broadside direction by placing the antenna at the top of FSS with an optimal air gap of 19 mm. The SWB ‘antenna-FSS’ exhibits wideband response over 3–36.2 GHz (169.4%) spectrum, including commercial ultra-wideband (3.1–10.6 GHz), ISM bands (5.725–5.875 GHz & 24–24.25 GHz), WiMAX (3.3–3.7 GHz), IEEE 802.11 WLAN bands, S-C-X-Ku-Ka bands, and 5G NR (n77, n78, n79, n257, n258, n261) bandwidth with stable and adequate gain of 5.2–7.16 dBi and an acceptable radiation efficiency.

Optically Transparent Tri-Wideband Mosaic Frequency Selective Surface with Low Cross-Polarisation.

Acquiring an optically transparent feature on the wideband frequency selective surface (FSS), particularly for smart city applications (building window and transportation services) and vehicle windows, is a challenging task. Hence, this study assessed the performance of optically transparent mosaic frequency selective surfaces (MFSS) with a conductive metallic element unit cell that integrated Koch fractal and double hexagonal loop fabricated on a polycarbonate substrate. The opaque and transparent features of the MFSS were studied. While the study on opaque MFSS revealed the advantage of having wideband responses, the study on transparent MFSS was performed to determine the optical transparency application with wideband feature. To comprehend the MFSS design, the evolutionary influence of the unit cell on the performance of MFSS was investigated and discussed thoroughly in this paper. Both the opaque and transparent MFSS yielded wideband bandstop and bandpass responses with low cross-polarisation (−37 dB), whereas the angular stability was limited to only 25°. The transparent MFSS displayed high-level transparency exceeding 70%. Both the simulated and measured performance comparison exhibited good correlation for both opaque and transparent MFSS. The proposed transparent MFSS with wideband frequency response and low cross-polarisation features signified a promising filtering potential in multiple applications.

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.

A Cascaded Tunable Wide Stop Band Frequency Selective Surface with High Roll-off Band Edge

A Cascaded Tunable Wide Stop Band Frequency Selective Surface with High Roll-off Band Edge

Low profile polarization‐insensitive wide stop‐band frequency selective surface with effective electromagnetic shielding

In this article, a polarization-insensitive, higher angular stability, and single-layered miniaturized wide stop-band frequency selective surface (FSS) is presented for effective electromagnetic shielding over an extremely wideband (9-20 GHz). A simple square gridded unit cell exhibits wideband rejection with −10 and −20 dB fractional bandwidth of 150.7% (3.4-24.2 GHz) and 74.5% (9.14-20 GHz), respectively. The designed unit cell has miniaturized dimensions (0.09λ0 × 0.09λ0 × 0.018λ0) as compared to existing research works on wideband FSSs. An equivalent circuit model is developed for the rigorous analysis of the proposed structure. The outcome of this circuit model is validated, and it shows good agreement with the structure simulation results. The measured results bear close resemblance with the simulated results. This FSS can be used to provide shielding from harmful radiations over a wide frequency range and as a good reflector to improve the gain of wideband antennas.

Wideband and Wide-Angle FSS Using Loop Slotted Hybrid Quarter-Mode Substrate Integrated Cavity With Two Independently Controllable Poles

A wideband and wide-angle frequency selective surface (FSS) is proposed in this communication. The periodic element consists of a quarter-mode substrate integrated waveguide (QMSIW) cavity surrounded by two identical loop slots located on the top and bottom layers of the cavity. Two transmission poles and one transmission zero are caused by the fundamental mode in the QMSIW cavity, the slot mode, and the coupling between them, respectively. By precisely tuning the dual-mode configuration, the proposed FSS shows a wide passband with a good transmission efficiency and a rapid roll-off at the high side of the operation band due to the transmission zero. With the QMSIW-based miniaturized elements, the FSS is also insensitive to a large angle of incidence. Thanks to the novel structure, several higher order modes close to the target band are suppressed, making the parasitic passband far away from both sides of the designed band. To verify the advantages, a prototype operated at 10 GHz is fabricated and tested. The measured results show a wide passband performance with the 1/3 dB relative bandwidths of 34%/49% for normal incidence, which agree well with the simulated results. Besides, the 3 dB bandwidth still remains 23% for the incident angle of 60°.

A miniaturized wideband frequency selective surface with interconnected cell structure

In this work, a sub-wavelength FSS with a novel interconnected open loop structure governed by coupling mechanism is proposed. An ultrawide stop-band ranging from 1.01 to 9.84 GHz is obtained with this structure. The proposed FSS is printed on both sides of a single substrate, with square loops on one side and interconnected open loop pairs on the other side. This FSS is ultra-miniaturized with a unit cell dimension of 0.04λ0×0.04λ0×0.0027λ0 where λ0 is the free space wavelength at the lower cut-off frequency. The designed FSS provides a stable bandwidth for TE and TM polarizations for oblique incident angles up to 45°. Parametric and circuit analysis is performed to validate the designed FSS. The fabricated prototype shows good concordance with the simulated model results.

Wide Transmission Band Frequency-Selective Rasorber Based on Convoluted Resonator

This letter proposes a wide transmission band frequency-selective rasorber (FSR) based on a convoluted resonator (CR). The FSR consists of a two-layered metallic structure with an air gap in the middle. At the top layer, the lumped-resistor-loaded metallic dipole with a CR inserted into the center is applied to generate wide absorption and transmission bands. At the bottom layer, the wideband frequency-selective surface is realized by a triple-layer metallic structure, in which two layers of identical square patches are coupled through a layer of the square aperture. The full-wave simulation results show that the wide transmission band with low insertion loss and wide absorption band are realized. To validate the performance of the proposed FSR, the prototypes are fabricated and measured, and reasonable agreement between the simulated and measured results is obtained. The measured results show that the transmission band with insertion loss less than 1 dB is covered from 9.00 to 12.63 GHz with 33.5% relative bandwidth. Compared with the previous FSRs with wide transmission band, the proposed FSR yields the widest relative bandwidth, better oblique performance, and simpler design.

Highly Transparent Frequency Selective Surface Based on Electrotextiles for On-Chip Applications

In this letter, a novel methodology using electrotextile fabrics is employed for designing a highly transparent, wideband frequency selective surface (FSS) in the millimeter-wave band. The standard metallization is replaced by a low-cost, extremely fine conductive mesh (RadioScreen or VeilShield) that gives to the periodic structure high see-through properties in the 27–35 GHz frequency band. An acrylic dielectric material that is easily available and very low-cost has been used as a substrate. Simulation and measurement results alike are presented to validate the principle. By assessing the high transparency properties of the FSS and its high performance in terms of stopband, this FSS could be seen as a potential candidate for multiple 5G applications like for on-chip shielding, autonomous vehicles, antenna and on-chip antenna devices, radar cross section augmentation, robotic guided paths, and electromagnetic interference protection.

Energy Saving Glazing and Its Compatibility with Heating, Antenna and Wireless Communication

<div class="section abstract"><div class="htmlview paragraph">Conductive heat reflecting automotive windows significantly attenuate RF communication signals. A number of methods are available to maintain electromagnetic compatibility and the function of these and other devices in the passenger compartment, while accruing the heat load reduction benefits of the coating. One of the methods is to integrate antennas on to the coated glazing and have glass antenna act as a communication interface between inside and outside of the vehicle. Another approach is to design a wideband or bandpass Frequency Selective Surface (FSS) window to facilitate wireless communication while preserving the thermal performance of the window. This paper provides detailed overview on coated antennas for vehicle communications, FSS window design for wideband and bandpass applications and coated antenna combined with de-ice and de-fogger functions with some designs and testing data.</div></div>

A Wideband FSS Based on Vias for Communication Systems

In this letter, a frequency-selective surface (FSS) structure by combining parallel LC resonators is proposed to achieve wideband performance. The metal vias are used to connect top layer and bottom layer so that the equivalent element in the circuit can be enlarged or minished. The metal vias minimize the unit size greatly, which achieves 0.0624 $\lambda$ . The bandpass performances of TE and TM polarizations are achieved by different parts— $S_{\text{TE}}$ and $S_{\text{TM}}$ , and the unit cell is further miniaturized by making cross with $S_{\text{TE}}$ and $S_{\text{TM}}$ . The FSS has steep roll-offs at the edges of the passband according to the simulated results. The prototype of the proposed FSS is manufactured and tested. The measured $-$ 3 dB bandwidth is from 1.3 to 4 GHz, and its relative bandwidth can achieve 110%. The thickness of the proposed FSS is 0.254 mm. The measured results show that the proposed FSS has better polarization and incident angle stabilities compared with other FSSs. This FSS is a good candidate to strengthen the detectivity performance of S -band active radar and isolate communication systems.

A 2.5-D Angularly Stable Frequency Selective Surface Using Via-Based Structure for 5G EMI Shielding

A novel broadband bandpass frequency-selective surface (FSS) designed for fifth generation (5G) EMI shielding is proposed in this paper. This new design employs the vertical vias into the 2-D periodic arrays, and such a single 2.5-D periodic layer of via-based structure is demonstrated to produce a highly stable angular response up to 60° for both TE and TM polarizations. By cascading two layers of such 2.5-D periodic arrays, the proposed FSS is able to obtain a broad passband as well as the wide out-of-band rejection. Moreover, it has a quite sharp band edge between the passband and the specified stopband. A corresponding equivalent circuit model (ECM) is further developed for better analysis of the operating principle. Finally, a prototype working at the center frequency of around 28 GHz is fabricated and measured. The main novelty of this paper is introducing the 2.5-D concept into designing a wideband FSS, and further reduce the unit size as well as improve the angular stability. Favorable agreement is achieved among the 3-D full-wave simulation, ECM and measurement. All these results demonstrate that the proposed FSS is a good candidate for 5G EMI shielding.

An explicit single-layer frequency selective surface design with wide stop band frequency response

AbstractThis manuscript deals with the development of a novel configuration of a wide-band single-layer frequency selective surface (FSS) for wide-band rejection applications. The established unit cell is composed of a simple circular ring on the top side of the substrate and a combined conductive element on the backside. Such an inclusion of conductive elements and accurate tuning of their dimensions ends in the rejection of a wide frequency band extended from 6.3 to 16.3 GHz. Moreover, the proposed structure exhibits a stable response against different angles of incidence for both TE and TM polarizations. Detailed simulation and measurement studies are carried out to investigate the performance of the proposed FSS. The obtained results are discussed in depth.

Polarization Insensitive Compact Wide Stop-band Frequency Selective Surface

Abstract A compact, polarization insensitive, wide stop band frequency selective surface is presented. The unit cell is designed by modifying the basic square loop FSS. The simulated value of bandwidth for transmission < ‒ 20 dB for TE incident wave is 7.7 GHz from 4.71 GHz to 12.41 GHz which is 89.95% corresponding to the center frequency of this range. It has an excellent band stop response for C and X band. The periodicity of the unit cell is the order of 0.33λ0 at the center frequency of 8.56 GHz. The total thickness of the proposed structure is 1.6mm (0.045λ0). Standard design formulas are used to evaluate the resonance frequencies and calculated values are found to be very close to the simulated ones. The proposed design is polarization insensitive and has good angular stability. An array of the proposed design is fabricated on either side of dielectric substrate FR4. The measured and simulated transmission responses are in good agreement. Proposed design can be used for many potential applications such as electromagnetic shielding, spatial filtering, sub - reflector in antennas and RCS reduction etc.

Broadband Polarization-Insensitive Tunable Frequency Selective Surface for Wideband Shielding

In this paper, a low-profile broadband frequency selective surface (FSS) is presented for wideband shielding. The FSS consists of periodic patterns of circular loops connected among themselves through varactor diodes, which exhibit tunable operation. The novelty of the proposed design lies in its wideband tuning, where the bandstop response can be varied from 0.54 to 2.50 GHz under the reverse bias voltage, thereby exhibiting a tunable range of 363%. Moreover, the structure exhibits a wide 1.28 GHz stopband (fractional bandwidth of 152%), which is maximum as compared to other wideband FSSs. Additionally, the design is polarization-insensitive and angularly stable for both TE and TM polarizations. A prototype of the proposed structure has been fabricated where the varactor diodes are biased through a novel biasing technique. The sample is measured using parallel-plate waveguide setup as well as the free-space technique, where the measured results show good agreement with the simulated responses.

A WIDEBAND FREQUENCY SELECTIVE SURFACE REFLECTOR FOR 4G/X-BAND/KU-BAND

A Frequency Selective Surface (FSS) reflector with wideband response for 4G/X-band/Ku-band is proposed. The wideband FSS reflector consists of cascaded dual-layer patch FSS which is etched on separ ...

An FSS-Backed 20/30-GHz Dual-Band Circularly Polarized Reflectarray With Suppressed Mutual Coupling and Enhanced Performance

A high-efficiency wideband frequency selective surface (FSS)-backed 20/30-GHz dual-band circularly polarized reflectarray antenna is presented. In order to effectively suppress the mutual coupling between the different element sets and improve the aperture efficiency, the variable element size and the element rotation angle phasing techniques are utilized in the multilayer reflectarray element designs at the Ka receive and transmit bands, respectively. Furthermore, a double-layer FSS with double concentric square loops is employed between the 20- and 30-GHz element layers. Thus, the uncoupled 20/30-GHz phase responses can significantly reduce the phase errors and simplify the dual-band reflectarray design process. To experimentally validate the performance of the proposed FSS-backed element configuration, an offset-fed 20/30-GHz dual-band circularly polarized reflectarray with a circular aperture of 400 mm is designed, fabricated, and measured. The measured gains are 36.7 dBic with aperture efficiency of 64.1% at 20.4 GHz and 40.2 dBic with aperture efficiency of 65.4% at 30.2 GHz, respectively. The measured aperture efficiencies exceed 47% within the whole receiving band (19.6-21.2 GHz) and 59% within the whole transmitting band (29.4-31 GHz), respectively. The proposed dual-band circularly polarized reflectarray antenna can be used for satellite communication applications at Ka-band.