Bandstop Frequency-selective Structure Research Articles

Implementation of 3-D Bandstop Frequency-Selective Structures With Ultralarge Angular Stability Utilizing Narrow L-Shaped Strip Lines

Implementation of 3-D Bandstop Frequency-Selective Structures With Ultralarge Angular Stability Utilizing Narrow L-Shaped Strip Lines

Dual-Polarization Multibandstop 3-D Frequency-Selective Structures Based on Cross-Coupling Method and Subcell–Cell Structure

In this article, based on cross-coupling way and subcell–cell structure, a methodology to design the low-profile dual-polarization multibandstop 3-D frequency-selective structure (FSS) is proposed. Using the 3-D periodic vertical placing printed circuit board pieces (PVPCB) structure, a first-order multibandstop FSS is proposed and analyzed first. For this first-order multibandstop FSS, the number of working stopbands is determined by the number of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> resonators in the edge of PVPCB structure. Then, this first-order multibandstop FSS is used as the basic resonator and crossly placed in the substrate of the PVPCB. This cross placement achieves the coupling between the basic resonators, and a single-polarization second-order bandstop FSS is obtained. Subsequently, this single-polarization second-order multibandstop FSS is used as the subcell, and a novel placement of this subcell ensures that the proposed second-order bandstop FSS can operate in dual-polarization with cross-polarizations of ≤−15 dB. In the whole modeling process, the equivalent circuit model is established to explain the working principle. Finally, to verify the proposed methodology, two examples with two and three working stopbands are designed, fabricated, and measured. The measured results show that the proposed dual-polarization FSS has stable filtering performance under different polarizations and oblique incident angle up to 30°.

A novel wideband absorptive frequency selective surface based on circuit analog absorber

In this paper, a single polarized absorptive frequency selective surface (AFSS) with ultra-wide transmission band and broad absorption band has been proposed numerically and experimentally. Based on the principle of circuit analog absorber (CAA), the proposed wideband AFSS is realized via replacing the ground plane with a band-stop frequency selective sturcture. The proposed AFSS is finally a hybrid structure composed of a wideband lossy frequency selective surface (FSS) in the top and a 3D band-stop frequency selective structure in the bottom. The wideband lossy FSS with thinner profile in the top is realized by utilizing a low pass capasitive elements to compensate the equivalent load inductance arising from the air space that is less than quarter wavelength installing between FSS and ground plane, and the low pass capactive lossy FSS is synthesized using “Gong”-shaped patterns with lumped resistors. Meanwhile, the unit cell of 3D frequency selective structure consists of two electrical coupling C-shaped patterns is investigated to achieve a wide stop band with high selectivity, which can be equivalent to the ground plane in the absorption band. By cascading the wideband lossy FSS and the 3D band-stop frequency selective structure, a thinner hybrid AFSS is presented with ultra-wide transmission band and broad absorption band. The results obtained from simulation shown that an absorption band with absorptivity above 90% is obtained from 6.6 to 11.6 GHz, and the 1 dB transmisson band is from 1 to 3.5 GHz with minimum insertion loss of 0.21 dB. Moreover, the performance can be guaranteed for TE-polarized oblique incidence up to 30°. Finally, a prototype is fabricated to validate its performance, the measured results shown that the 1 dB transmission band ranges from 1 to 3.5 GHz, and the absorption band is operating from 6.3 to 11 GHz at normal TE-polarized incidence. A good agreement between the experiment and simulation results is achieved, which verifies the effectiveness of the design.

Low-RCS and Beam-Steerable Dipole Array Using Absorptive Frequency-Selective Reflection Structures

This communication presents an approach to design a beam-steerable dipole array with low radar cross section (RCS). A 2-D periodical array of dipole antennas is colocated with absorptive frequency-selective reflection (AFSR) structures to effectively reduce the out-of-band RCS and maintain high gain at the in-band frequencies. The AFSR structures consist of 3-D bandstop frequency-selective structure (FSS) and pyramidal-shaped absorbers to provide a reflection band for the dipole array with enhanced front-to-back ratio. Compared with the reference array, the radiation performance of the proposed array is maintained with an aperture efficiency of 70% and a measured peak gain of 21.5 dBi. The beam-steering angle is up to ±45°. Meanwhile, more than 10 dB two-sided out-of-band RCS reduction is achieved with a bandwidth of 96.5% and 30% for copolarization and 142% for cross polarization, and the in-band RCS is unchanged.

Broadband Band-Absorptive Frequency-Selective Rasorber With a Hybrid 2-D and 3-D Structure

A novel frequency-selective rasorber (FSR) with a broad absorption band is proposed in this letter. The proposed FSR is realized by vertically cascading a two-dimensional (2-D) lossy layer with a 3-D band-stop frequency-selective structure (FSS). The 2-D lossy layer is composed of meandered square loops loaded with lumped resistors, and the 3-D band-stop FSS is constructed by parallel-plate waveguide arrays (PPWAs) stacked along the TE polarization direction (linear polarization perpendicular to the PPW). The band-absorptive FSR exhibits an absorption band (| S 11| ≤ –10 dB and | S 21| ≤ –10 dB) from 7.85 to 12.85 GHz and a low-pass band (| S 21| ≥ –1 dB) up to 3.8 GHz. Its transition efficiency of the transition band (FRap) is 2.1. A prototype is fabricated, and its measured results show that the proposed FSR has a low loss and flat low-pass band, a wide absorption band with high selectivity, and a steep transition band between the low-pass band and absorption band.

A Theoretical and Experimental Study of Frequency-Selective Structures for Reducing the Scattering Properties of a Phased Antenna Array

Abstract—A theoretical and experimental study of band-stop frequency-selective structures (FSSs) for reducing the scattering properties of linear antenna arrays outside of their operating band is presented. To perform the study, a two-layer FSS based on square loops located in different layers of the dielectric base has been selected. An electrodynamic simulation of the backscattering diagram (BSD) of a linear periodic structure shielded by the FSS has been carried out. An effect of nonsuppression of certain diffraction scattering lobes has been discovered and experimentally confirmed. The discovered effect has been physically explained and measures to eliminate it have been proposed. The results of the electrodynamic simulation of an antenna system consisting of an L-band phased antenna array (PhAA), a two-layer FSS located in front of the PhAA, and an absorbing material are presented.

Bandstop Frequency-Selective Structures Based on Stepped-Impedance Loop Resonators: Design, Analysis, and Measurement

A new dual-polarized and dual-band second-order bandstop 3-D frequency-selective structure (FSS) is proposed with arbitrary band ratio. Compared with the square loop, the stepped-impedance (SI) loop resonator performs at lower basic resonant frequency and increases the first spurious resonant frequency. Different half-wavelength SI loop resonators are analyzed, compared, and employed to design single/dual-band 3-D FSSs under TE polarization. A double-sided SI loop resonator with via holes is presented for constructing a dual-polarized single band FSS. By adjusting widths of low characteristic impedance sections, the FSS's band can be expanded into dual bands. Detailed analysis of the coupling between both identical resonators in series is provided for understanding the relationships between subresonators. In addition, the equivalent circuit models are developed to explain the operating principle and analyze parameter effects. The proposed FSS prototype is fabricated and then measured to verify the design methodology. The measured results agree with the simulated data and exhibit a dual-polarized and stable second-order bandstop response under different incident angles up to 30°. The thickness of the structure is 23% of the free-space wavelength at the first center frequency, and the center frequency ratio of both stopbands is only 1.08.

Thin Bandstop Frequency-Selective Structures Based on Loop Resonator

Circular and elliptical loop resonators are proposed as the unit cell of 3-D frequency-selective structure aiming to reduce the structure thickness. The structure exhibits a pseudoelliptic response by utilizing the coupling between the two quasi-TEM modes, which are concentrated in air and substrate regions of the unit cell. Using elliptical loop with stepped-impedance resonator (SIR), the thickness of the structure can be reduced by 80% compared to previous structures. A comparison between the response of the structure employing the microstrip line as the resonator and the structure using the proposed loop resonators is performed. Three prototypes are designed, fabricated, and tested. The first structure is designed to have a dual-band bandstop response using two half-circular loops with end via holes; it has center frequencies at 10 and 14.3 GHz with −3 dB fractional bandwidths of 6.7% and 6.6%, respectively. A half-elliptical loop with SIR is employed in the second structure to achieve more thickness reduction. The third structure is designed to exhibit a dual-polarized bandstop response. Stable frequency response under various angles of incidence is obtained.

Design of Wideband Bandstop Frequency-Selective Structures Using Stacked Parallel Strip Line Arrays

We present a novel design procedure to implement wide bandstop frequency-selective structures using the periodic arrays of vertically stacked parallel strip lines (PSLs). The proposed structures employing the PSLs can simplify their design through equivalent circuit models. Three structures are designed based on the simple equations to demonstrate the proposed procedure. The first structure features an independent design of the air and substrate regions, allowing the use of higher order resonances to extend the bandwidth. The second structure employs a cascaded array, and the third represents a hybrid of both the first and second structures. Design examples have been provided for each proposed structure, achieving −10 dB fractional bandwidths of 78%, 100%, and 137% for the first, second, and third structures, respectively. The operating principles and the design procedures are explained along with the experimental verification for the first two structures.

Miniaturized Bandstop Frequency-Selective Structure Using Stepped-Impedance Resonators

This letter describes a miniaturized bandstop frequency-selective structure (FSS) based on the stepped-impedance resonator (SIR). The FSS consists of a two-dimensional periodic array of vertical microstrip SIRs for thickness reduction. A shunt capacitor connecting the SIR center and ground is employed to widen the operating bandwidth and to improve the quasi-elliptic filtering response. It is shown that more than 40% thickness reduction of the FSS can be realized by choosing a small impedance ratio of the SIR, and a steep quasi-elliptic bandstop filtering performance is achieved by adjusting the value of the shunt capacitor. As an example, a prototype of the proposed FSS is designed, fabricated, and tested. The good agreement between simulated and measured results verifies the design concept of the miniaturized FSS.