Reconfigurable Frequency Selective Surface Research Articles

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.

Reconfigurable screen-printed terahertz frequency selective surface based on metallic checkerboard pattern

We employed the screen-printing method to fabricate terahertz (THz) frequency selective surfaces (FSSs) featuring an inductive metallic checkerboard (i-MCB) pattern based on conductive silver ink onto a flexible polyethylene terephthalate substrate, chosen for its excellent THz transmission properties below 1 THz [Jin et al 2006 J. Korean Phys. Soc. 49 513–17]. Analytical studies, along with simulations and experiments, were conducted to investigate the filtering characteristics of the printed FSSs, confirming their functionality as a band-pass filter. Subsequently, we demonstrated the reconfigurability of a two-layer system by vertically stacking two layers. This was achieved by systematically shifting the position of the second layer in the x or y-direction relative to the first layer. Experimental verification revealed a significant variation in normalized transmission, ranging from 94% to 6% at 0.15 THz for type-I:i-MCBs and 90% to 5% at 0.20 THz for type-II:i-MCBs, respectively. This study presents a simple scheme for a reconfigurable screen-printed i-MCB-FSS operating in the THz range. Consequently, our findings demonstrate that screen printing method can effectively be employed for the large-scale production of THz FSSs.

A Multifunctional Reconfigurable Frequency Selective Surface with Simultaneous Switching and Tuning Capability

A Multifunctional Reconfigurable Frequency Selective Surface with Simultaneous Switching and Tuning Capability

Broadband Polarization Reconfigurable Frequency-Selective Surface Design

Broadband Polarization Reconfigurable Frequency-Selective Surface Design

A broadband reconfigurable frequency-selective surface in terahertz band based on different metal-insulator transition temperature of VO<sub>2</sub>

A broadband reconfigurable frequency-selective surface in terahertz band based on different metal-insulator transition temperature of VO<sub>2</sub>

3-D polarization insensitive ultrawideband frequency selective rasorber with switchable transmission band

A novel polarization insensitive ultrawideband frequency selective rasorber (FSR) based on a 3-D cubic structure is proposed, and the fundamental operating principles of the three parts are demonstrated by equivalent circuit models. The first one is a 3-D FSR based on the multiple resonant absorptions of the curved longer dipole and shorter dipole excitation in the resonance chamber and the insertion of the interdigital resonator (IR) structure in the shorter dipole to form a transmission window. The passband with an insertion loss of less than 3 dB is 10.3–12.9 GHz (22.4%), and the frequency bandwidth with a reflection coefficient of less than −10 dB ranges from 4.2 to 20.5 GHz (132%). The second is a reconfigurable frequency selective surface (FSS) with two operating states, and the third is a 3-D FSR with a switchable passband feature that incorporates the above two structures of loaded switching diodes.

A Two-Stage Beamforming Antenna Using Butler Matrix and Reconfigurable Frequency Selective Surface for Wide Angle Beam Tilting

A two-stage beam-forming technique for a wide tilt angle is proposed in this letter. The proposed structure has the potential to overcome the limitations of Butler matrix-based beam-forming technique and reconfigurable FSS-based beam-forming technique, both of which normally lag behind in the present generation of wireless communication due to lesser number of radiating beams. The composite system comprises three parts: a 4 × 4 Butler matrix, an antenna array of 1 × 4 elements, and a reconfigurable FSS layer. Four semi-rigid coaxial cables are employed to connect the Butler matrix to the four-element antenna array. The reconfigurable FSS is mounted on top of antenna layer using air spacers. The FSS superstrate layer consists of 6 × 6 reconfigurable unit cells, which have been further divided into two equal sections to increase the number of radiating beams. Combining the four-port Butler matrix with reconfigurable FSS allows the system to generate twelve unique radiating beams in twelve distinct directions in three-dimensional space. The proposed system is designed, fabricated, and measured for operating frequency of 5.5 GHz. The proposed system attains a maximum tilt of 72° and peak gain of 11.8 dBi.

Wide-Passband Reconfigurable Frequency Selective Rasorber Design Based on Fluidity of EGaIn

In this letter, we propose a wide-passband reconfigurable frequency selective rasorber (FSR) design based on the fluidity of liquid metal. To achieve wide-passband reconfigurability, a new type of reconfigurable frequency selective surface with wide-passband elliptic filter response is introduced for the first time, whose bandpass state can be switched to a perfect reflection state by controlling the injection and the extraction of liquid metal in microchannels. Furthermore, a new resistive film loop with a minimum insertion loss of 0.23 dB is presented by loading four circular spiral resonators. Finally, the FSR can realize the reconstruction of the absorption-transmission-absorption (ATA) and absorption-reflection-absorption (ARA) modes. The simulation results show that in ATA mode, the design exhibits a wide passband with a fractional 3 dB bandwidth reaching up to 42.8%, and a passband minimum insertion loss of 0.86 dB at 13 GHz. In ARA mode, the bandwidth for return loss less than 3 dB is 12.8%. Prototypes were fabricated and measured. Compared with previous FSRs, our proposed FSR has advantages such as reconfigurable characteristics, a wide transmission band, and high-frequency selectivity.

Design of broadband dual‐polarised reconfigurable frequency selective surface based on dual‐branch parallel circuit model

AbstractA broadband dual‐polarised reconfigurable frequency selective surface (RFSS) based on general dual‐branch parallel circuit model is proposed by the authors. The specific circuit model is constructed to feature the switchable functions of transmission and reflection characteristics by introducing a parallel branch. It is beneficial to clarify the operating mechanism and provide an effective guidance to satisfy the switching bandwidth requirements of the desired RFSS. In order to validate the proposed concept of the dual‐branch parallel circuit model, a broadband dual‐polarised RFSS prototype has been designed, fabricated and measured. A satisfactory agreement can be reached between the synthesis, simulation and measurement. The experimental results exhibit the merits of low insertion loss, broad switching bandwidth and good angular stability for different polarisation and different incident angles.

Reconfigurable Terahertz Moiré Frequency Selective Surface Based on Additive Manufacturing Technology

We designed and fabricated a terahertz (THz) frequency selective surface (FSS) based on two distinct additive manufacturing technologies, namely, printable electronics (PE) and three-dimensional (3D) printing. Silver nanoparticle ink was printed on a polyethylene terephthalate (PET) substrate utilizing a large-scale roll-to-roll industrial PE technique with a flexographic printed unit, while the 3D-printed THz FSS was fabricated based on a powder bed fusion-selective laser melting system. The filtering characteristics of both types of FSS were verified through calculation, simulation, and experiments. Furthermore, the rotational tuning approach was applied to two identical FSS to form reconfigurable FSS which could be defined as Moiré FSS. Based on the numerical results obtained, our proposed technique which used a PE-based Moiré FSS achieves a 58% modulation depth at 0.25 THz, while experimental verification found a modulation depth of 41% at 0.22 THz, confirming that its adoption is simple and cost-effective. To the best of our knowledge, this is the first demonstration of a Moiré reconfigurable printed FSS operating in the THz region.

A Reconfigurable Frequency Selective Surface for Wi-Fi Application

This work presents the development of a reconfigurable frequency selective surface (RFSS) for application in the 2400-2483.5 MHz band, standard IEEE 802.11b/g/n (Wi-Fi). The proposed RFSS is based on the four-arms star geometry and PIN diodes were used as switching elements. In the initial design, numerical and measured results, especially for y polarization, PIN diode on-state, shown a difference of 15% for the resonant frequency. To overcome this drawback, a scaling factor was adopted and RFSS was redesigned and characterized, achieving the desired frequency response. The RFSS reconfigurability is confirmed, with a variation of at least 15 dB, when switching the states of the PIN diode. Moreover, the signal strength was measured directly on a notebook, confirming the reconfiguration of the RFSS. Finally, for the y polarization, it was found that for this polarization the frequency response remains virtually unchanged, even for angles of incidence up to 45°. In addition to the Wi-Fi signal control, the observed features make the developed RFSS especially attractive for reconfigurable antennas applications.

Polarization-Insensitive Absorptive/Transmissive Reconfigurable Frequency Selective Surface With Embedded Biasing

In this letter, a polarization-insensitive absorptive/transmissive reconfigurable frequency selective surface (RFSS) using p-i-n diodes is presented. The RFSS structure incorporates two periodically arranged metallic patterns on both sides of an FR4 dielectric substrate, where the p-i-n diodes are aligned symmetrically on the bottom surface. Depending upon the diode biasing conditions, the geometry behaves as a radar absorber and a bandpass filter under different working states. The simulated response exhibits a near-unity absorption response (having absorptivity of 93.51%) at 6.93 GHz during <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> state of the diode, whereas the incident electromagnetic wave gets transmitted through the structure at 5.62 GHz during <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> state. An embedded biasing circuitry has also been developed comprising metallic vias and inductors, such that the geometry displays polarization-insensitive and angularly stable responses for both states. The structure has been analyzed with the help of circuit modeling and other parametric variations to explain the switching methodology. A prototype has been fabricated and measured using the parallel-plate waveguide technique, which results in a good agreement with the simulated responses. Such RFSSs can be marked as a potential element for various radome applications.

A Polarization-Insensitive Dual-Band FSS With High Selectivity and Independently Switchable Characteristics

The investigation of dual-band frequency selective surface (FSS) has attracted a great deal of attention over the past few decades. However, the existing reconfigurable dual-band FSSs exhibit first-order responses with poor frequency selectivity. In this letter, a polarization-insensitive dual-band FSS with a rotationally symmetrical receiver–transmitter unit-cell configuration that exhibits a second-order response is presented. p-i-n diodes are loaded on separate layers to achieve the independent switching of two passbands. The full-wave simulation results are presented, and an equivalent circuits model is also presented to analyze the operation principle of the proposed FSS. The measurement results of our fabricated prototype indicate that the device exhibits two independently switchable polarization-insensitive transmission bands centered at 3.06 and 4.33 GHz. The shape factors representing the selectivity of the transmission band are 2.44 and 2.46, respectively, which are approximately 1/4–1/2 times that of the existing reconfigurable dual-band FSSs. The proposed FSS exhibits angular stability up to 40 <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> below 5 GHz. This work paves the way toward high selectivity reconfigurable dual-band FSS.

A Liquid Sensor Based on Frequency Selective Surfaces

A novel, simple and easy-to-fabricate liquid sensor using frequency-selective surfaces (FSSs) is proposed. The new sensor concept is based on modifying the capacitance between adjacent FSS elements when materials of different electrical characteristics are inserted. The change in capacitance produces a change in resonant frequency. The FSS design consists of a 9 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 9 array of square loops on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.31\lambda \times 0.31\lambda $ </tex-math></inline-formula> square unit cells with trenches between the loops. The trenches are filled with liquids under test (LTUs). The structure operates at 4.6 GHz without any liquid. When liquids are inserted in the trenches, the resonance frequency varies in relation to the dielectric constant of the liquid. This is observed by measuring the transmission coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> ). Butan-1-ol, ethanol, methanol, propan-2-ol, and xylene are used to demonstrate the sensing function. A maximum sensitivity of 8.65% for xylene was achieved. Furthermore, very low differences were observed between the measured and expected dielectric constant and loss tangent, thus validating the design. The device is inexpensive, compact, and easy to make and scalable for large-area operations in liquid detection for microwave sensing applications. This technique has potential applications in reconfigurable FSS.

Reconfigurable Frequency Selective Surfaces for X Band Applications

Reconfigurable Frequency Selective Surfaces for X Band Applications

Use of Thermochromic Properties of VO2 for Reconfigurable Frequency Selection

The thermochromic nature of vanadium dioxide (VO2) has facilitated many promising applications for reconfigurable frequency selectivity. The phase-changing property of VO2 was used to realise a reconfigurable frequency-selective surface (FSS) capable of manipulating electromagnetic waves for different functionalities. Diffractive optical elements (DOE) are used for diffracting laser beams to form conductive FSS images on the VO2 wafer for frequency selectivity. The dipoles on the VO2 wafer generate a stop band response of 12 dB and 10 dB for unit cells of the single dipole and double dipole at 3.5 GHz, respectively. A 10 GHz FSS array is projected by DOE on the 2-inch VO2 wafer with a filtering effect of 13 dB at 9.5–10.5 GHz. This solution is used to design a radar cross-section (RCS) modification FSS with reflected waves of about 20 dB higher reflectivity in the backscattering direction than in the specular direction.

Reconfigurable Frequency Selective Surfaces With Complementary Reflection and Transmission Responses Using Duality Theorem-Based Elements

Reconfigurable frequency-selective surface (FSS) designs that come with switchable reflection and transmission bands are developed. According to the duality theorem, complementary periodic structures made of similar wire and slot elements shall yield opposite scattering responses. This is facilitated by placing diodes between tips of the proposed #-shaped wire elements. In the reverse-bias state, disconnected elements act as a band-stop-type FSS. By providing a forward bias, connected elements are transformed into a slot array, which generates an inverted passband at the designated resonant frequency. The proposed periodic structure comprises one layer of microstrip line laid on a thin substrate. The #-shaped elements also act as the biasing network for serially connected diodes. Only one bias voltage is needed to control the FSS panel. Range setups and signal processing techniques are devised so that simulated results of infinite FSS can be compared with measured results. By including diode’s equivalent circuits in simulation models, good agreements with prototype measurement results are observed. The complementary reflection and transmission characteristics can be forwarded to advance radome and antenna designs to achieve versatile performance features.

A system‐level performance evaluation of a reconfigurable filtenna in the presence of in‐ and out‐of‐band blockers

Direct RF sampling has been suggested as a solution for receivers that are flexible in frequency and across standards, while utilising only a single radio frequency front-end. However there are concerns about their robustness in the presence of out-of-band and in-band blockers. Tunable filtennas offer a solution to this, incorporating filtering into the antenna space while providing rejection of unwanted signals. This paper presents a filtenna containing reconfigurable frequency selective surfaces to provide tunable filtering between 1.44 and 1.95 GHz. The filtenna is characterised as an antenna and a filter, showing minimum 18 dB rejection across the principle beamwidths. It is then implemented in a direct RF sampling receiver and is shown to provide sufficient rejection of blockers to cause no degradation in the received error vector magnitude (EVM) and block error rate (BLER) of LTE signals when subject to 5G NR-compliant blocking signals. The in-band blocker performance is also characterised, showing at most 3 dB degradation in EVM and BLER.

A high angle stable and polarization symmetric dual band reconfigurable frequency selective surface

Abstract A dual band reconfigurable active frequency selective surface is designed which resonates at 2.5 and 3.6 GHz as transmission pole frequencies. Lower and upper pass bands have −3 dB bandwidths of 0.4 and 0.5 GHz, respectively. Two notch frequencies are configured from 4.71 to 3.5 GHz and from 2.78 to 2.45 GHz. Dimensions of the unit cell are optimized to λ 0/10 calculated at the lowest resonance. The proposed design exhibits insignificant variation at oblique excitation angles until 75° of dual polarized plane wave. An equivalent circuit model is developed for optimization and vivid understanding of the structure behaviour. A prototype of the designed structure is fabricated and the measured response is in satisfactory agreement with the simulated transmission response. High angle stability, low insertion loss at both the transmission pole frequencies, dual band pass/stop tuning for single and dual polarized wave with use of only two varactor diodes are eminent features of the design.

Development of Reconfigurable Frequency Selective Surface Associating Cross Dipoles and Matryoshka Geometries

A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geometries is described in this paper. The proposed reconfigurable FSS uses as active element PIN diodes. With the associated geometries, three resonant frequencies are achieved, two fixed, related to the matryoshka geometry, and one that can be activated or not, related to the cross dipoles geometry. Differently from previous works, an inductor was inserted into the cross dipoles’ horizontal arms, maintaining its resonance for x polarization. The PIN diode inserted into cross dipoles’ vertical arms controls the respective resonance. The design procedures for each geometry, in addition to PIN diode and RF inductor basics are outlined. The expected results are discussed based on the analysis of the resonances of each geometry and the associated geometries, as well as the different PIN diode bias states (OFF and ON). A prototype was fabricated and characterized, obtaining a good agreement between the numerical and experimental results, with a reconfiguration bandwidth of 0.24 GHz, from 2.12 GHz to 2.36 GHz, for a variation of at least 10 dB between the OFF and ON states.