Bandstop Frequency Selective Surface Research Articles

Band-Stop Frequency-Selective Surface (FSS) with Elliptic Response Designed by the Extracted Pole Technique.

This paper describes and validates an advanced synthesis design process of Frequency-Selective Surfaces (FSSs) with elliptic band-stop responses. A systematic procedure based on the Generalized Chebyshev Function and the extracted pole technique enables control of the position of the transmission zeros and the attenuation level to obtain an equiripple rejection response. A systematic process is followed to obtain the lumped LC values of the resonator circuits extracted as poles and the impedance inverters. Then, equivalent dipoles and transmission lines are obtained to carry out the electromagnetic design at normal incidence for a linearly polarized field. The impact of the higher-order modes of the periodic structure on the electrical response of the FSS, which can be relevant due to the stringent selected specifications, has been also analyzed. A fourth-order band-stop filter with a 3 GHz bandwidth centered at 30 GHz and its attenuation at 50 dB has been designed considering three different implementations: two filters using a vacuum as a transmission line with different connection lengths and a third one using a dielectric substrate to enable its manufacturing. In order to verify the design procedure using experimental results, the third filter with printed dipoles in the dielectric substrate has been manufactured and measured, thus validating the developed process.

A high Q factor sensor to measure the complex permittivity and effective permittivity based on a band stop frequency-selective surface

In this paper, a metamaterial sensor is proposed based on a band stop frequency-selective surface (FSS) with high Q factor of 421.9 at 8.032 GHz. The sensor consists of a square loop FSS and a F4B dielectric substrate. This is the first sensor based on a band stop FSS sensing the effective permittivity of 3D printed hollow structures. The equivalent circuit method is used to analyze the characteristics of the sensor, and the results agree well. Two materials under test and four different hole radii of 3D printed hollow structures are used to verify the sensing function. At the same time, the effective permittivity of the 3D printed hollow structure is analyzed, and the correctness of the effectiveness is verified by simulation inversion and Maxwell-Garnett formula. The sensor has the advantages of high Q factor, wide incidence angle and polarization angle insensitivity, which can provide some guidance in metamaterials sensing.

Design of single layer bowtie wide band-stop frequency selective surface with angular stability for C-band applications

This paper presents the design and analysis of a single-layer wide band-stop frequency selective surface (FSS) tailored for C-band applications. The proposed FSS design employs a modified bow-tie unit cell structure that enhances band stop characteristics, resulting in improved performance compared to traditional FSS geometry. The design process involves numerical simulations and optimization techniques to achieve the desired frequency response. A modified bowtie element with FR4 substrate comprises the proposed FSS which exhibits a resonant frequency of 6.0 GHz with a wide bandwidth of 4.84–6.96 GHz (35.93 %) and act as a band stop filter. The FSS is analyzed in terms of its transmission coefficients, providing insight into its filtering properties. In addition, parametric studies of the unit cells are done. Furthermore, the angular stability of the proposed FSS is simulated with incident waves at various angles between 0° to 60° for both TE and TM modes. The proposed FSS presents C-band applications of WLAN, ISM/WiMAX, satellite communications, radar systems, shielding and communication devices, also enhancing filtering capabilities and system performance. The simulation results are well correlated with measurement results.

Dynamic frequency switching of a bandstop reconfigurable frequency selective surface with PIN diodes for C/X and Ku-band shielding applications

This paper presents a reconfigurable bandstop frequency selective surface (R-FSS) design capable of switching across C, X and Ku-bands. The electronic switching mechanism is achieved in real-time through PIN diodes. The combination of rectangular loops is selected as unit-cell and PIN diodes are strategically placed to dynamically adjust the bandstop region. The device operates in three distinct modes corresponding to the activation status of the PIN-diodes. For TE polarization, Mode 1 encompasses the Ku-bandstop (12.64–14.75 GHz), Mode 2 corresponds to the C/X-bandstop (6.62–11.28 GHz), and Mode 3 involves the X-bandstop (9.82–11.63 GHz), whereas X-bandstop characteristic is observed for TM polarization (9.054–––11.29 GHz). In TE polarization, each configuration is defined by specific equivalent circuit models, featuring an inductance in parallel with series L-C resonant circuit, an L-C resonant circuit in parallel with the inductance, and two L-C resonant circuits in parallel, respectively. Additionally, for TM polarization, the configuration incorporates two parallel L-C resonant circuits. A prototype of the proposed R-FSS is fabricated and measured. The results demonstrated effective switching operation across the C, X and Ku-band stopbands, depending on the biasing of the PIN diodes. The experimental outcomes are consistent with the simulation results, affirming the compatibility and functionality of the proposed R-FSS design.

Polarization-insensitive graphene-based band-notched frequency selective absorber at terahertz

This paper introduces a new polarization-insensitive graphene-based frequency selective absorber (FSA) with a reflective notch designed for terahertz applications. The proposed structure features two absorption bands on either side of a central reflection band. The design composes a lossy frequency selective surface (FSS), a bandstop FSS with a metal backing, and an air spacer between. A wideband absorber structure is developed in the first step, leveraging graphene as an absorbent material in the lossy layer to achieve wideband absorptive characteristics. Subsequently, a reflection band is introduced by integrating a bandstop, lossless FSS layer into the absorber structure. The overall structure demonstrates two distinct absorption bands, characterized by absorptivity exceeding 80% within the frequency ranges of 0.30 to 0.57 and 0.67 to 0.90 THz. Simultaneously, a reflection notch is achieved at 0.60 THz. Extensive simulations assessed the performance of the designed FSA. The proposed structure exhibits stability under oblique incidence up to 40 deg and allows tunable absorption specifications by adjusting the chemical potential of graphene. It is noteworthy that the FSA reflector offers advantages such as eliminating the need for complicated, high-cost 3-D structures and welding of the lumped resistors.

A double-layered C-band frequency-selective surface bandstop filter for maritime communication

ABSTRACT In this paper, a dual-bandstop frequency-selective surface (FSS) implemented using a four-legged Minkowski square and s hexagonal ring is presented. The proposed FSS shows dual stopbands at 4.9 GHz and 7.1 GHz in the C band. The size of the unit cell is 0.36λ0 × 0.36λ0, which is designed on an FR4 substrate with a thickness of 1.6 mm and a loss tangent of 0.02. The frequency response of the bandstop FSS is verified using circuit simulation, and its optimised dimensions are determined at the desired frequencies of operation. The results reveal that the ratio of the two stopband frequencies can be adjusted over a wide range by properly selecting the geometrical parameters. The impedance bandwidths for S11< –10 dB of 0.9 GHz and 1 GHz have been realised at the lower and upper frequency bands, respectively. A prototype is fabricated and measurements show a reasonable agreement with the simulated results, thus validating the design concept. It has been shown that the proposed bandstop FSS exhibits excellent stability upto 60° at oblique incident angles in both TE and TM polarisations. This FSS is suitable for C-band maritime applications due to wide stopbands and highly stable angular operation.

Stable scanning angle, polarization-insensitive band-stop frequency selective surface for wireless communication

Stable scanning angle, polarization-insensitive band-stop frequency selective surface for wireless communication

Notice of Retraction: Carbon-Reinforced Flexible Band-Stop Frequency Selective Surface Design

Notice of Retraction: Carbon-Reinforced Flexible Band-Stop Frequency Selective Surface Design

A Proposed Frequency Selective Surface (FSS) using Bio-Inspired Element for Wi-Fi 6E Applications

Recently bio-inspired elements with shapes or geometries found in nature have received special attention, both for applications in antennas and in electromagnetic filters, the unit cell of the proposed FSS consists of a modification in a bio-inspired shaped element. A single and multilayered band-stop Frequency Selective Surface (FSS), with polarization independence, is proposed to be used in frequency applications at 6.0 GHz (Wi-Fi 6E). In the industry, Wi-Fi 6E is the name that identifies those Wi-Fi devices that operate in the 6.0 GHz band, designed to improve efficiency and more capacity than previous standards. Band-stop frequency responses for the single and multilayer structures are presented. The simulated frequency responses show bandwidth values for inhibit transmission about of 1.75 GHz and 3.15 GHz, respectively for single and multilayer structures. Furthermore, good agreement between simulated and measured results is shown for the single bio-inspired FSS. The proposed FSS structure presents features that allow its use as an electromagnetic filter or its integration with microstrip antennas developed for applications in the same standard.

COMPARATIVE ANALYSIS OF EMBROIDERY AND SCREEN-PRINTING TECHNIQUES FOR TEXTILE-BASED FREQUENCY SELECTIVE SURFACES

Frequency Selective Surface (FSS) is a specialized structure used in the field of electromagnetic waves and radio frequency (RF) engineering. It is designed to exhibit selective transmission or reflection properties based on the frequency of the incident electromagnetic waves. This article describes the design, construction, and analysis of a textile-based band-stop frequency selective surface for use in the highly EM-polluted GSM, Wi-Fi, LTE, and WiMAX bands. A full-wave EM solver called CST Microwave Studio was used to develop and simulate the unit cell of the proposed FSS at the relevant frequency. In this study, embroidered and screen-printed textile based FSSs were designed. According to the results of this study, it was demonstrated that both embroidery and screen printing FSSs exhibit resonance at a frequency of 3.5 GHz. The screen printing method yielded the best results in terms of resonance frequency sensitivity, while the embroidery method showed a resonance frequency shift. It was observed that the stitch directions and density are important parameters in the embroidery method. Gaps between the embroidery paths in the production of embroidered FSSs resulted in differences from simulations due to the disruption of the structural integrity of the unit cell. Consequently, textile-based FSSs offer advantages over traditional FSSs. This study highlights the potential of textile FSSs as an effective means of reducing electromagnetic pollution, and suggests that further improvements in the design and production processes of textile FSSs can be made.

Polarization–Insensitive Angularly Stable Compact Triple Band Stop Frequency Selective Surface for Shielding Electromagnetic Radiations

Polarization–Insensitive Angularly Stable Compact Triple Band Stop Frequency Selective Surface for Shielding Electromagnetic Radiations

Receiving and Transmitting Antenna Pairs Based Rasorber With High Angular Stability

Frequency selective rasorbers (FSRs) with out-of-band absorption and in-band transmission performance have been widely reported for stealth radome applications over the past few years. However, developing an FSR with high angular stability in the transmission band remains challenging. Therefore, to improve the transmission angular stability, we propose an innovative architecture in this work for constructing the FSR with independently explorable absorption and transmission paths. First, a band-stop frequency selective surface (FSS) and an absorber are employed in the absorption path to obtain out-of-band absorption. Second, the receiving (RX) and transmitting (TX) antenna pairs connected by the corresponding enclosed transmission lines (TLs) are utilized to comprise the transmission path. Note that a wide-beam RX antenna is employed to capture incident electromagnetic (EM) waves at large angles and achieve in-band transmission with high angular stability. Besides, another second-order FSR with a sharp roll-off transmission filtering response is proposed by using the second-order band-stop FSS as the ground (GND) of the RX antenna. Furthermore, two prototypes of the FSRs (one narrowband and the other second-order) are fabricated and measured as demonstrations of the proposed architecture. Experimental results agree with simulation ones, indicating the two devices exhibit the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 3-dB transmission bands with excellent angular stability of 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> , and both transmission windows are located on a wide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 10-dB low reflection band.

Model analysis of embroidered FSS and evaluation of production

This article presents the design, fabrication, and analysis of a textile-based band-stop frequency selective surface (FSS), in GSM, Wi-Fi, LTE, and WiMAX bands where the electromagnetic (EM) pollution is intense. The unit cell of the proposed FSS has been designed and simulated via a full-wave EM solver; CST Microwave Studio at the frequency of interest. In this study, embroidered textile-based FSSs were designed as an alternative to conventional FSSs. In the study, high textile detailed (from thread to embroidery direction) modeling was performed and the results of the modeling and experiments were compared. The results of this study showed that the embroidery direction has a dramatic effect on the electromagnetic behavior of the FSS. Both experimental and high textile detailed modeling results indicated that vertical or horizontal embroideries are not sufficient for band-stopping FSS. To overcome this problem, vertical-over-horizontal embroidery was used. The highly textile detailed model and its experimental results have proven that horizontal-over-vertical embroidery is successful in band-stopping FSS.

A monostatic RCS reduction study for an antenna in structural mode at X band

ABSTRACT In this paper, a radar cross-section (RCS) reduction of a microstrip antenna is investigated both experimentally and numerically. A traditional metal ground plane antenna and a bandstop frequency selective surface (FSS) filter are designed at 5.4 GHz. In order to reduce RCS and reflectivity of the reference antenna, the bandstop filter structure is set up instead of the full metal ground plane. The study observed a wide frequency range between 3 GHz and 14 GHz. The maximum RCS reductions between the reference antenna and the low RCS antenna in-band and out of band are obtained at 9.2 dBsm and 28 dBsm, respectively. The antennas are analysed under different θ – and φ – polarised incidence conditions. Low RCS antenna shows satisfactory results especially at X band in terms of reflectivity and RCS under these angular conditions.

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

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

Flexible Ink-Minimized Screen-Printed Frequency Selective Surfaces With Increased Optical Transparency for 5G Electromagnetic Interference Mitigation

A thin, flexible and transparent polyethylene terephthalate (PET) based screen-printed band-stop Frequency Selective Surface (FSS) with ink minimization is experimentally demonstrated at 28 GHz using both planar and conformal configurations. A miniaturized conventional FSS unit cell is ink-minimized using surface meshing without compromising the angular stability of the transmission response of the surface within ±60°. This not only leads to reduced amount of expensive ink required in prototyping, thereby lowering the overall manufacturing cost, but also increases the optical transparency of the structure by a factor of 65% using an 80 μm line-width tolerance. Finally, the operation of the ink-minimized FSS is experimentally shown using a conformal geometry with two radii of curvature (60 mm and 114 mm) and a good filtering performance is confirmed. Useful for 5G electromagnetic interference (EMI) applications, these FSSs feature increased feasibility through improved transparency and reduced cost due to ink minimization.

Design and Implementation of a Textile-Based Embroidered Frequency Selective Surface

This article presents the design, fabrication and analysis of a textile-based band-stop frequency selective surface (FSS), in GSM, WiFi, LTE and WiMAX bands where the electromagnetic (EM) pollution is intense. The unit cell of the proposed FSS has been designed and simulated via a full-wave EM solver; CST Microwave Studio at the frequency of interest. In contrary to traditional FSS designs, which are printed on solid materials such as PCBs, this study presents an FSS considering a woven fabric as a substrate layer having features such as flexibility and compact weight. Two fabrication techniques have been considered one is conducted with a copper tape having a thickness of 35 µm denoted as CT FSS and the second one is conductive yarn embroidering technique denoted as CY FSS for the conducting pattern. Fabricated samples are evaluated in terms of transmission characteristics and a satisfactory agreement is obtained between CT FSS and CY FSS for both simulations and fabricated prototypes.

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.

High directivity microstrip antenna with stopband and passband frequency selective surfaces for 6G at low-THz

There is still no high-directivity microstrip antenna with directivity beyond 25 dBi, bandwidth (BW) of more than 24%, which can be used for 6G cellular communication at low-THz at a resonance frequency of 144 GHz. So, duo broadband microstrip antennas have been designed at a resonance frequency of 144 GHz with the Taconic TLY-5 laminate in this work. These designs were carried out with the computer simulation technology microwave studio (CST MWS) software. The first antenna simulation results were compared within an Ansys high-frequency structure simulator (HFSS) software, and the obtained simulation results from both software were in fair consent, supporting the proposed designs. The peak directivity, peak gain, total peak efficiency, and BW obtained for the proposed THz microstrip antennas were 27.01 dBi, 25.3 dB, 78.96%, and 34.21 GHz (24.93%), respectively. Therefore, these antennas can be a base for 6G at low-THz.

A dual-transmission-bands rasorber with improved absorption and oblique incidence performance

In this paper, a high-absorption and dual-transmission-bands rasorber (HADTR) was proposed. Different from the reported designs, a foam layer and a FR4 layer are added as top layers in HADTR to improve its absorption and oblique incidence performance. The unit cell of resistive layer is concentric metallic rings loaded with chip resistors based on absorption enforced design to ensure its dual-transmission-bands at the same time. The unit cell of band-stop frequency selective surface (BS-FSS) is double metallic square loops loaded with chip inductors on both sides of FR4 substrate, which expands its reflection band (|S11|≥ − 1.0 dB) without destroying its dual-transmission-bands effectively. At normal incidence, for TE and TM polarization, the HADTR has a low-frequency passband up to 1.34 GHz (|S21|≥ − 1.5 dB), a high-frequency passband from 16.04 to 18.00 GHz (|S21|≥ − 1.5 dB) and a wide 90% absorption band from 5.01 to 10.56 GHz; and the reflection coefficient below − 10 dB and − 20 dB is in the range of 4.48–11.70 GHz and 5.48–9.96 GHz, respectively. For TE/TM polarization, the 90% absorption of oblique incidence stability is 40° and 30° respectively. Strong association between measurement and simulation results validates the design method and the HADTR.