Frequency Selective Reflector Research Articles

Investigations on relevance of angular stability and polarization independence of frequency selective reflector in planar antenna gain enhancement

The relevance of angular stability (AS) and polarization independence (PI) is investigated by rotating the frequency selective reflectors (FSRs) kept behind a 10 GHz triangular slot antenna in orthogonal directions. Three distinct frequency selective surfaces (FSSs) based on closely packed rhombic loop (RL), square loop (SL) and merged dual rhombic loops (MDRL) are developed for the analysis under normal and oblique incidences. The gain enhancement of 4.87, 7.17 and 4.85 dB is achieved when the antenna is backed by 5 × 5 arrays of RL, MDRL and SL FSS, respectively. Later, with equal sized substrates, the gain enhancement of 7.25, 7.17 and 8.10 dB is achieved when the antenna is backed by 61 × 61 mm2 RL, MDRL and SL FSSs, respectively. It appears that stringent characteristics of FSSs i.e. AS and PI can be compromised for FSRs while employing antenna gain enhancement techniques.

Dual-Notched UWB Orthogonal MIMO Antenna with Improved Gain Characteristics Using Frequency Selective Surfaces for Wireless Communication Applications

In this paper, a complementary split ring resonator (CSRR) loaded compact CPW-fed circular shaped monopole UWB antenna with dual band notch characteristics is designed on an FR-4 substrate. The propounded band-notched UWB antenna is integrated with two frequency selective surface layers referred as bandpass frequency selective surface (FSS-1) and reflector (FSS-2) to offer enhanced radiation performance. Bandpass FSS-1 enhances the gain of the antenna by improving directivity and reflector FSS-2 reflects back the backside radiation of the proposed antenna towards the forward direction thereby increasing gain and directivity of the proposed antenna. Furthermore, a two-element orthogonal MIMO antenna is proposed with improved gain using two FSS layers. The complete configuration of the proposed two-element MIMO antenna consists of CSRR-based radiating patches, monopole ground planes and two integrated FSS layers. The proposed MIMO antenna operates in UWB range from 3.46[Formula: see text]GHz to 16.02[Formula: see text]GHz with dual notches at 3.9[Formula: see text]GHz and 7.2[Formula: see text]GHz. Isolation between MIMO elements is greater than 23 dB. Both antennas are fabricated and investigated at 5.9[Formula: see text]GHz for vehicular communications. Maximum gain improvements of 8 dB and 6.4 dB are observed in case of the presented single element and MIMO antenna within the entire operating band due to the integration of dual FSS layers. The diversity performance of the suggested MIMO antenna is investigated by analyzing mean effective gain, envelope correlation coefficient, channel capacity loss and diversity gain parameters. The proposed MIMO antenna is a suitable candidate for vehicular and UWB wireless communication applications.

Absorptive Frequency-Selective Reflector With Switchable Reflection Band and Its Application in RCS Reduction of Antennas

Absorptive Frequency-Selective Reflector With Switchable Reflection Band and Its Application in RCS Reduction of Antennas

Tunable Janus absorptive frequency-selective reflector with octave frequency absorption.

A tunable Janus absorptive frequency-selective reflector (AFSR) utilizing a graphene-based hyperbolic that showcases exceptional doubling octave frequency absorption (DOFA) or tripling octave frequency absorption (TOFA) is proposed. The multi-objective gray wolf optimization algorithm is employed to drive the transfer matrix method, optimizing parameters such as the dielectric permittivity, thickness, and the Fermi level (Ef) to achieve harmonic absorption. By manipulating the Ef of graphene, the dimensions of the absorption band and reflection window can be finely adjusted. Additionally, a frequency-selective reflector is introduced, enabling a seamless transition between selective absorption and transmission by adjusting the Ef. This AFSR represents a groundbreaking approach to achieving DOFA or TOFA while simultaneously offering valuable insights into the design of intelligent AFSRs.

A Low-RCS Circularly Polarized Reflectarray Antenna With a Linearly Polarized Feed

A low-radar cross section (RCS) circularly polarized (CP) reflectarray antenna with a linearly polarized (LP) feed is designed. The out-of-band RCS of the reflectarray for both the TE and TM polarized incident waves is reduced by replacing its ground with an absorptive frequency selective reflector (AFSR). A systematic methodology based on synthesis of the equivalent circuit model (ECM) is presented to expedite the design of the AFSR. The unit phasing element of the reflectarray is designed in such a way that it exhibits minimum coupling between the two orthogonal reflected LP-field components. Moreover, during the reflectarray construction, a novel phase synthesis is used which takes into account possible lowest of the existing mutual coupling while providing quadrature phase difference between the orthogonal LP components with minimum phase error. The proposed design is fabricated using 14×14 phasing elements to experimentally validate the numerically simulated results. The performance of the reflectarray is compared with a conventional reflectarray without the AFSR. It is observed that when the reflectarray is integrated with the AFSR, its gain is reduced only by 1.16 dB. However, its out-of-band RCS is reduced significantly. The 8-dB RCS reduction bandwidth can be observed from 3.55-7.2 GHz (67.9%) and from 11.85-14.21 GHz (18.11%). Moreover, it provides peak co-pol CP gain of 21.62 dBi, aperture efficiency of 41%, and 1-dB gain-bandwidth from 8.68-8.95 GHz, respectively.

Ka-band cryogenic low-noise receiver of the Misasa 54 m antenna for deep-space communications and radio astronomy

Abstract We built a Ka-band dual-circular-polarization low-noise receiver for the Misasa 54 m parabola antenna in Misasa, Japan. The antenna is designed to be combined with a transmitter and receiver system at the X band (around 8 GHz) and simultaneously with a receiver system at the Ka band. The Ka band is the frequency band around 30 GHz, which is important for deep-space communications and radio astronomy. The receiver comprises some waveguide components including a feed horn, a circular polarizer, and low-noise amplifiers. The components are installed in a vacuum vessel and are cooled to 4 K with a Gifford–McMahon refrigerator, providing low-noise performance. The receiver is capable of simultaneously handling the left- and right-hand circular-polarization (LHCP and RHCP) channels. The receiver-noise temperature was measured to be TRX ≃ 14 K in both the LHCP and RHCP channels. The system-noise temperature, including the antenna loss and atmospheric attenuation at the zenith, was measured to be Tsys = 36–37 K in both the LHCP and RHCP channels on a clear day in September at Misasa. When the receiver is used with the X-band transmitter, the system-noise temperature is maintained at Tsys ≃ 42 K in the RHCP channel. The degradation in the system-noise temperature is attributed to a frequency-selective reflector, which divides the signals in the X and Ka bands. There is no contamination from the transmitter to damage the receiver. The receiver has already been in use for deep-space communications and radio-astronomy observations. Our team in the radio-astronomy laboratory of ISAS/JAXA is responsible for the development of the receiver and the measurements of its performance.

Electromagnetic Functional Surfaces Related to Frequency Response Control Using Back-Loaded Radio Frequency Circuits

A novel scheme for designing electromagnetic functional surfaces (EMFSs) is proposed in this article. Different from traditional frequency selective surface (FSS), this scheme uses the antenna array and the back-loaded radio frequency circuit (BLRFC) to control the frequency response of EMFSs. The antenna array and the BLRFC can be designed independently resulting in great design flexibility and functional diversity. The sharp skirt out-of-band suppression and tunable frequency response can be achieved by using this scheme. Three design levels (element level, subarray level, and array level) are introduced to illustrate the design philosophy. Several EMFSs are designed, and one of them has been fabricated and measured. Actually, the prototype is a dual-polarized absorptive frequency selective reflector (AFSR). For both TE and TM polarizations with normal incidence, the AFSR exhibits one reflection band with 3 dB bandwidth from 10.6 to 16.3 GHz, two absorption bands with the absorptivity greater than 90% from 6 to 10 GHz, and from 16.8 to 19 GHz. The AFSR has a stable angular performance up to 50°. All the design examples and fabricated prototype verify the flexibility and the superiority of the novel scheme, and a multiplicity of EMFSs can be realized by using the BLRFC technique.

Wideband Low RCS Antenna Based on Hybrid Absorptive-Diffusive Frequency Selective Reflector

A method for designing a wideband low radar cross section (RCS) antenna is proposed based on hybrid absorptive and diffusive frequency selective reflector (AD-FSR) in this paper. The low RCS antenna exhibits manifold frequency responses in three artificial bands, which are created by its different components. A simple U-slot patch antenna is borrowed, which is integrated with the diffusion metasurface, and placed under the absorptive sheet with about quarter wavelength. Then, the out-of-band incident wave is captured by the absorber in the lower frequency band, and diffused by the metasurface in the upper frequency band achieving the RCS reduction. The design strategies are explained and verified with the aid of the corresponding equivalent circuit model and current distributions. To illustrate the efficacy of the proposed approach, the low RCS antenna using the proposed hybrid AD-FSR structure is fabricated and tested, and the results demonstrate that the proposed structure is an attractive candidate for designing wideband low RCS antennas.

Absorptive Frequency-Selective Reflector Based on Bent Metallic Strip Embedded With Chip-Resistor

A new methodology for designing a dual-polarized absorptive frequency-selective reflector (AFSR) with wide reflection and absorption bands is proposed in this communication. The AFSR is made up by an array of interweaved bent metallic strips embedded with chip-resistors in the center on a metallic ground. The absorption–reflection–absorption response is obtained by generating multimode resonance with wave antinode and wave-node characteristics of the proposed structure. Four metallic strips are interweaved together to realize dual-polarized performance for its rotational symmetry characteristic. The designed AFSR is fabricated and measured, and the measured results agree well with simulation. It is shown that the measured fractional 3 dB reflection bandwidth is 46.2% between two absorption bands. In addition, the AFSR has stable performance for both TE and TM polarizations under various oblique incidence angles up to 40°, and the whole profile of the structure is only $0.076~\lambda _{L}$ , where $\lambda _{L}$ is the lowest frequency of the operating frequency band.

One-way and near-absolute polarization insensitive near-perfect absorption by using an all-dielectric metasurface.

In this Letter, we numerically propose the one-way perfect absorption of near-infrared radiation in a tunable spectral range with high transmission in the neighboring spectral ranges. This functionality is obtained by using a two-dimensional, guided-mode resonance-based grating-waveguide metasurface that acts as a frequency-selective reflector, a spacer dielectric, and an absorbing oxide layer. Within the bandwidth of the excited guided-mode resonance excited at 1.82 µm (with a full-width at half-maximum of 19 nm), we confirmed perfect absorption when light was incident from one of the two opposite directions, whereas in the other direction, perfect reflection was observed. The forward-to-backward absorption ratio reached as high as 60, while the thickness of the entire structure was on the order of the operating wavelength. In addition to the spectral tunability of the excited resonances and their bandwidths, our proposed device supports transparency windows with 65% transmission in the adjacent frequency bands. Our 2D grating is also verified to enable near-absolute insensitivity to the polarization state of incident light. Geometrical parameter modification also gives our design great tunability, as we also designed a device with a 300 nm absorption/reflection linewidth.

An Absorptive Frequency Selective Reflector With Wide Reflection Band

In this paper, an absorptive frequency selective Reflector (AFSR) with wide reflection band is proposed. The structure is divided into two layers: a resistive sheet at the top layer, and PEC at the bottom layer, divided by polymethacrylimide (PMI) foam. The resistive sheet layer is composed of a multiple bended strip resonator (MBSR) in the center and two metallic strips loaded with resistors beside MBSR. Two metallic strips loaded with resistors can be equivalent to serial RLC, and the MBSR can be equivalent to parallel LC circuit. The MBSR is mainly used to realize absorption performance beside reflection band and contribute to one of the reflection bands with different resonant modes. The resonant frequencies are adjustead to obtain the wider reflection band. Full-wave simulation results show that the reflection band of the proposed AFSR cover from 8.94 GHz to 15.1 GHz with |S 11 | > -1 dB. The relative bandwidth is 52%. Compared with the earlier reported AFSR, this proposed AFSR owns the widest reflection band and simple structure. In addition, the absorptive bands with |S 11 | <; -10 dB are separately located at 3.6 GHz-6.11 GHz and 15.23 GHz - 16.19 GHz. The analysis and the design are presented in this paper. To evaluate the effectiveness of the design, the prototype of the proposed AFSR was fabricated and measured. The measured results are in good agreement with the simulated results.

Quality factor improvement of piezoelectric MEMS resonator by the conjunction of frame structure and phononic crystals

Recently, piezoelectric resonators fabricated by using MEMS (i.e., micro-electro-mechanical systems) technology have received increasing attention in a large and diverse set of applications, including sensors, filters and timing references. One of the critical challenges for the actual application of MEMS resonators is further improving their quality factors (Qs) to respond the urgent demand of performance enhancement. Herein, a strategy by employing suspended frame structure and phononic crystals (PnC) was proposed to reduce the energy dissipation, and thus AlN-on-SOI MEMS resonators with high Q were successfully implemented. The suspended frame structure isolates the mechanical vibration between the resonant body and the anchoring substrate, while PnC arrays serve as a frequency-selective reflector to reduce the energy leakage. The multi-physics finite-element-analysis (FEA) and the experimental comparison were employed to systematically investigate the underlying mechanisms of the energy dissipation reduction of the proposed strategy. The unloaded Qs (i.e., Qu) of proposed resonators achieved maximum 7.8-fold and 1.5-fold improvements compared with that of bared resonators and that of those with only suspended frame structure, respectively.

Frequency Selective Rasorber and Reflector With Two-Sided Absorption Bands

A design to achieve frequency-selective rasorber (FSR) and reflector with two-sided absorption bands is proposed. The theoretical analysis and the calculation method for the structure parameters are presented by utilizing the equivalent circuit model. The reflector and the rasorber are designed in simple 2-D structures, consisting of only one layer of resistive sheet and a pure ground or a bandpass frequency-selective surface, respectively. Based on the analysis of the condition for realizing two-sided absorption, we found that the parameters of each element in the resistive sheet are correlative and proportional to each other. The calculation method of actual physical dimensions of the proposed structure is provided, so the element sizes of unit cell structure can be calculated and designed to approximate the desired values. Hence, based on these proposed methods, the perfect two-sided absorption FSR or reflector can be realized directly when the deduced relationship of the parameters is satisfied. Therefore, the approach of impedance matching becomes much easier. The simulation results show the two wideband absorption bands located above and beneath the reflection/transmission band. An FSR and a reflector are designed, fabricated, and measured. The measurement results match well with the simulation results and verify the designing principle. The FSR realizes the two-sided absorption bands at 2.1–5.1 and 11.9–17.5 GHz and a transmission band at 9.7 GHz. The reflector shows a wide reflective bandwidth and two wide absorption bands at 2.8–6.5 and 12–17.4 GHz.

3-D Absorptive Frequency Selective Reflector for Antenna Radar Cross Section Reduction

A methodology for designing a frequency selective reflector with two-sided absorption bands is proposed. This method is based on utilizing multimode resonators inside a 3-D unit cell to obtain an absorption-reflection-absorption response. Detailed analysis of this 3-D absorptive frequency selective reflector (AFSR) is provided with the aid of an equivalent circuit model to reveal the operating principle. To show the benefit of the new structure in antenna’s radar cross section reduction (RCSR), a dual-polarized 3-D-AFSR integrated with monopole and dipole antennas are simulated, fabricated, and then measured. Compared with their counterparts with normal ground plane, AFSR-backed antennas have shown a remarkable out-of-band RCSR. The −10 dB RCSR has fractional bandwidths of at least 64.7% and 41% with center frequencies of 3.4 and 8.3 GHz, respectively. The radiation characteristics of AFSR-backed antennas are nearly maintained. The realized gains are enhanced by 0.9 and 2.3 dB for monopole and dipole antennas mounted on a 3-D-AFSR, respectively.

HPBW control of dipole antenna with frequency selective reflector using different size elements

HPBW control of dipole antenna with frequency selective reflector using different size elements

Quasi-Static Magnetic Field Shielding Using Longitudinal Mu-Near-Zero Metamaterials.

The control of quasi-static magnetic fields is of considerable interest in applications including the reduction of electromagnetic interference (EMI), wireless power transfer (WPT), and magnetic resonance imaging (MRI). The shielding of static or quasi-static magnetic fields is typically accomplished through the use of inherently magnetic materials with large magnetic permeability, such as ferrites, used sometimes in combination with metallic sheets and/or active field cancellation. Ferrite materials, however, can be expensive, heavy and brittle. Inspired by recent demonstrations of epsilon-, mu- and index-near-zero metamaterials, here we show how a longitudinal mu-near-zero (LMNZ) layer can serve as a strong frequency-selective reflector of magnetic fields when operating in the near-field region of dipole-like sources. Experimental measurements with a fabricated LMNZ sheet constructed from an artificial magnetic conductor – formed from non-magnetic, conducting, metamaterial elements – confirm that the artificial structure provides significantly improved shielding as compared with a commercially available ferrite of the same size. Furthermore, we design a structure to shield simultaneously at the fundamental and first harmonic frequencies. Such frequency-selective behavior can be potentially useful for shielding electromagnetic sources that may also generate higher order harmonics, while leaving the transmission of other frequencies unaffected.

Design of a high‐gain ultra‐wideband planar dipole antenna using LC tanks, chip resistors, and dual‐layer frequency selective surface

AbstractIn this article, a low‐profile, high‐gain, ultra‐wideband (UWB) planar dipole antenna is presented for radar imaging applications. The antenna is loaded with open complementary double concentric split‐hexagonal‐ring resonators (LC tank) and chip resistors, and backed with a novel double‐layer frequency selective surface reflector for gain enhancement. A broadband microstrip to parallel‐plate transformer is designed as the feeding structure of the antenna to provide impedance matching and balanced‐to‐unbalanced transition. The measurement results show the proposed antenna operates over the frequency bandwidth of 0.65–3.8 GHz with S11&lt; −10 dB (VSWR) and smooth gains in the range of 6.2–9 dBi. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2369–2373, 2014

A low‐profile dual‐layer ultra‐wideband frequency selective surface reflector

AbstractAn ultra‐wideband (UWB), dual‐layer frequency selective surface (FSS) is presented.This compact low‐profile FSS has been designed as a reflector for UWB antennas. It can be inserted between a planar UWB antenna and a nearby parallel conducting surface such as a circuit board, screen, or a metal case, to isolate them and to prevent antenna impedance mismatch otherwise caused by the conductor. The measured transmission coefficient magnitude of the FSS is less than −10 dB over a 133% bandwidth and its reflection phase is appropriate for this and other similar reflector applications, over an UWB. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1223–1227, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27583

A Compact Dual-Band Pattern Diversity Antenna by Dual-Band Reconfigurable Frequency-Selective Reflectors With a Minimum Number of Switches

A novel compact dual-band pattern diversity antenna is proposed. Dual-band reconfigurable frequency-selective reflectors are designed and applied to form a right-angle corner reflector antenna with reconfigurable patterns. With only one switch, the reconfigurable frequency-selective reflector can be controlled to be transmissive or reflective to vertically polarized waves at 2.45 and 5.25 GHz. By changing the combinations of the switch states, multiple patterns can be obtained. A dual-band feeding antenna designed via using the coupling effects is made to achieve well-matching conditions in all circumstances corresponding to various switch states at both frequencies. The measured results show good agreement with the calculated ones and demonstrate good pattern diversity virtues.

A Novel Pattern Diversity Reflector Antenna Using Reconfigurable Frequency Selective Reflectors

A radiation pattern diversity reflector antenna is investigated. Novel switchable frequency selective reflectors are designed and developed to construct a square corner reflector antenna. By controlling a switching device on the frequency selective reflector, one can make it opaque or transparent to a vertically polarized incident wave. This antenna is fed by a monopole. By configuring the switch states of the frequency selective reflectors, various beam shapes can be formed and steered. Measured results of the antenna show good agreement with the calculated ones.