Bandstop Structure Research Articles

A simple miniaturized sub‐6‐GHz bandpass filter with wide upper stopband in gallium arsenide‐based integrated passive device process

AbstractA very compact three‐pole bandpass filter with wide upper stopband is proposed and implemented by gallium arsenide integrated passive device technology. By organizing inductor and capacitor in parallel with an LC series network, a dual‐frequency bandstop structure is constructed in the first step to achieve transmission zeros (TZs). Then, the lowpass capacitor network and highpass inductor network are wisely cascaded with the bandstop structure, thus to the realization of three‐pole bandpass filter with a wide upper stopband. Based on the even‐/odd‐mode analysis, theoretical equations for the in‐band resonances and out‐of‐band TZs are given. Then, one filter prototype centered at 4.4 GHz with 3‐dB fractional bandwidth of 45.5% is designed, fabricated, and measured. Both simulated and measured results indicate that the proposed filter exhibits a wide stopband rejection of 25 dB from 6.4 to 22.8 GHz as well as a very compact size about 0.026λg × 0.031λg.

Bandgap structure in elastic metamaterials with curvy Bezier beams

This Letter discusses elastic metamaterials incorporating curved beams in their architecture. Through employing Bezier splines, we reveal a wide versatility of geometrical designs of the unit cells and the consequent programmability of bandgap structures. By analyzing more than ten thousand possible specimens altogether, we highlight the similarity between dynamic properties of metamaterials formed by curves with different geometries defined via three variables only that correspond to the coordinates of control points of the Bezier spline. In particular, we establish the importance of such parameter as effective curve length in defining the probable positions of bandgaps. This study shows, in particular, that the bandgap ratio can reach 71% for metamaterials with proposed curved beams—a noticeable contrast with no bandgaps in their counterpart with straight elements. The employment of the deep learning model enables us to effectively predict passband–stopband structure in such metamaterials with satisfactory accuracy, potentially accelerating the design of metamaterials assembled from versatile unit cells.

Broadband Fixed-Beam Leaky-Wave Antenna With Consistent and High Gain Based on Ridge Gap Waveguide

In most communication scenarios, antennas are often required to achieve broadband and directional radiation, and beam squint with frequency is unfavorable for broadband signal transmission. The traditional leaky-wave antennas (LWAs) have beam squint with frequency. In this letter, an LWA with fixed beam direction in a broadband is designed with consistent gain over the band. A ridge gap waveguide (RGW) is adopted to construct a nondispersive structure, and one lateral side is connected to a parallel plate filled with dielectric slab. Thus, leakage radiation is produced at the interface between the RGW and the parallel plate, generating a beam with fixed direction and high gain. The novelty is that in theory the fixed beam can be realized in infinite band owing to the nondispersive waveguide. Finally, a broad band of up to 58% (from 22 to 40 GHz) is achieved due to the limitations of the stopband structure and feeding port. The measured beam is fixed at 41° over the whole band, with a slight beam deviation of 2.6°. The realized gain is consistent over the band with a peak gain of 19.3 dBi. The designing method provides a simple and efficient way to realize the broadband fixed-beam LWAs.

Nonlinear dispersion properties of one-dimensional mechanical metamaterials with inertia amplification

Architected metamaterials offering superior dynamic performances can be conceived by inducing local mechanisms of inertia amplification in the periodic microstructure. A one-dimensional cellular lattice characterized by a pantograph mechanism in the tetra-atomic cell is proposed as minimal physical realization of inertially amplified metamaterial. A discrete model is formulated to describe the undamped free dynamics of the cell microstructure. The ordinary differential equations of motion feature quadratic and cubic inertial nonlinearities, induced by the indeformability of the pantograph arms connecting the principal atoms with the secondary atoms, serving as inertial amplifiers. An asymptotic approach is employed to analytically determine the dispersion properties governing the free propagation of harmonic waves in the pantographic metamaterial. First, the linear wavefrequencies and waveforms are obtained by solving the eigenproblem governing the lowest asymptotic order. An invariant parametric form is achieved for the pass and stop band structure, corresponding to propagation and attenuation branches of the dispersion spectrum in the plane of complex wavenumbers. The major effects due to the mass ratio of the inertial amplifiers are discussed. Particularly, the existence conditions, amplitude and centerfrequency of the band gap separating the acoustic and optical pass bands are determined analytically. Second, the nonlinear wavefrequencies and waveforms are obtained by solving the hierarchical linear problems governing the higher asymptotic orders. Analytical, although asymptotically approximate, functions are achieved for the nonlinear wavefrequencies and waveforms, which show quadratic dependence on the oscillation amplitudes. The mechanical conditions for the softening/hardening behaviour of the nonlinear wavefrequencies and the different topological properties of the invariant manifolds associated to the nonlinear waveforms are discussed. Finally, numerical simulations are provided to validate the analytical results.

A Novel Miniaturized Strong-Coupled FSS Structure With Excellent Angular Stability

In this article, a novel miniaturized concept named strong-coupled frequency selective surface (SC-FSS) with excellent angular stability is presented. First, a conceptual design of SC-FSS is introduced, where the resonant frequencies are insensitive to almost all incident angles. A corresponding equivalent circuit model is developed to interpret the operating principle and formulate relevant design equations with an error of 0.2%. Furthermore, an ultraminiaturized and ultrathin band-stop structure with a unit cell size of λ 0/35 and thickness of 0.26 mm ( λ0 /578) is designed and fabricated to verify this concept. Analysis and experiment show that the proposed band-stop SC-FSS structure can work stably at 2 GHz for both TE and TM modes, even when the incident angle varies from 0° to 84°. The measurement results are consistent with those obtained by full-wave simulations and the equivalent circuit model, which fully demonstrates that the concept of SC-FSS can be widely used in designing antenna reflectors, electromagnetic interference shielding, and angle-insensitive absorbers.

Compact wide stopband microstrip lowpass filter using polygon patches and meandered lines

In this paper, a low pass filter based on T-Shaped resonator is presented. The T-Shaped resonator consists of meandered lines and rectangular patches. Also, the LC model and transfer function of the proposed resonator is presented. For suppression of spurious harmonics, a bandstop structure consists of hexangular patches and open stubs has been utilized. Finally, the wide stopband microstrip lowpass filter with cutoff frequency 2.72 GHz has been simulated, fabricated and measured. The LPF has good characteristics such as wide stopband and insertion loss lower than 0.18 dB in the passband region. The rejection level is less than -20 dB from 2.98 up to 21.3 GHz. The filter size is 10.5 mm×12.7 mm, or 0.131 λ<sub>g</sub>× 0.158 λ<sub>g</sub>, where λ<sub>g</sub> is the guided wavelength. The measured and simulated results of the filter is in good agreement with each other, which show the merits of low insertion loss and wide stopband.

Wideband Diplexer With Narrow Channel Spacing Using Hybrid Bandpass-Bandstop Structures

In this paper, a wideband diplexer with narrow channel spacing is designed by using hybrid bandpass-bandstop structures. Two wideband bandpass structures are designed with the transmission zeros at the upper or lower passband edges to achieve high skirt selectivity. Two bandstop structures based on half-wavelength coupled lines are integrated to the two bandpass structures to introduce additional transmission zeros and thus the skirt selectivity is further improved. Accordingly, two channel filters with high skirt selectivity and high stopband rejection are designed to realize a wideband microstrip diplexer with very narrow channel spacing. For verification, a wideband diplexer operating at 1.71-2.17 GHz and 2.30-2.70 GHz is implemented, which covers multiple frequency bands for different mobile systems. The measured results show excellent performance of passband flatness, high in-band isolation of better than 35 dB and low minimum insertion losses of 0.46 and 0.50 dB for the two channels.

Compact filtering power divider with extended stopband using out‐of‐phase feeding scheme

A compact filtering power divider is proposed with very wide stopband suppression in this letter. First, the dual-composite right- and left-handed (D-CRLH) resonator is employed, while one extended stopband can thus be achieved due to its inherently slow-wave response. Secondly, one out-of-phase feeding scheme is introduced to realise D-CRLH filtering power divider. By putting the input and output ports on the different sides of D-CRLH resonators, the mismatching can be realised for the harmonics below 10 GHz and wide stopband suppression is obtained accordingly. For experimental verification, a compact filtering power divider is designed, fabricated, and measured. Wide stopband suppression is observed until 5 f 0 without using bandstop structures or complex coupling topology.

An Ultra-Wideband Bandpass Filter with a Notch Band and Wide Upper Bandstop Performances

This paper presents an ultra-wideband bandpass filter (UWB-BPF) with a notch band and a wide upper stopband. Two pairs of half-wavelength high-impedance line resonators tightly and strongly coupled to the input/output lines are used to provide the wideband responses. The first UWB responses of 3.4–5.0 GHz and the second UWB of 6.0–10.0 GHz are designed independently first and then combined together for the application of a direct-sequence ultra-wideband bandpass (DS-UWB) system. Without using any extra bandstop structure, a notch band at 5.2 GHz can be obtained. The fabricated UWB-BPF with a compact circuit size exhibits good passband performances including insertion losses of 1 ± 0.3 and 2 ± 0.4 dB for first and second passbands, respectively, a high isolation at 5.2 GHz with an attenuation level of 22.7 dB, and wide upper stopband responses from 11 GHz to 19 GHz, simultaneously. The measured results also exhibit good agreement with the simulated results.

Realization of Multiple Transmission Zeroes for Bandpass Filters With Simple Inline Topology

The realization method of multiple transmission zeroes (TZs) for second-order bandpass filters (BPFs) is presented in this brief. A modified filter topology with mixed couplings is investigated at first. With the cancelation effect of electric and dominant magnetic couplings, two close-to-passband TZs can be easily realized for a second-order inline filter. Furthermore, the dual-function feature of loaded quarter-wavelength ( $\lambda $ /4) resonators is analyzed. Besides of filtering response, $\lambda $ /4 resonators can be used to realize two more TZs in the stopband. At last, multiple open stubs are loaded asymmetrically at feeding lines, each of which can generate one TZ independently. Due to the asymmetric loading, the extra circuit area of bandstop structures is reduced by half. For demonstration, a wideband BPF using $\lambda $ /4 resonators and four asymmetric open stubs is designed, fabricated, and measured. The stopband suppression can be improved to 10.2 GHz without sacrificing in-band properties or enlarging circuit size. Good agreement can be observed between the measured and simulated results of the proposed BPF.

Multifunctional Bandpass Filters With Reconfigurable and Switchable Band Control

A new series of multifunctional reconfigurable bandpass filters (BPFs) and their analytical synthesis design are presented in this paper. They feature frequency-adaptive characteristics in both their passbands and notched bands, as well as switchable-notched-band capability. Their basic filter architecture is discussed and modeled in a progressive manner. The initial circuit consists of a second-order Chebyshev-type filter to which two stubs are added to increase filtering selectivity through transmission-zero (TZ) creation. Subsequently, to produce an embedded notched band, stubs acting as band-stop structures are also inserted at the input–output terminals. The multifunctional properties of this filter scheme are analyzed attending to the resonance frequencies of the introduced stubs. When these resonance frequencies are tuned while keeping a constant spacing between them, a center-frequency reconfiguration with constant bandwidth is achieved; when the resonance frequency of the notched band is shifted to the TZ positions, the notched band is switched-off. The described filter synthesis methodology is based on the constant and frequency-mapping technique, where the dual-mapping functions are controlled to obtain reconfigurable/switchable properties from a low-pass prototype. For experimental-validation purposes, two reconfigurable lumped-element filter prototypes using the proposed synthesis technique are designed, manufactured, and tested. One exhibits a simple reconfigurable passband, whereas the other one adds a controllable/switchable embedded notched band that results in a quasi-elliptic-type dual-passband response. When compared to some related prior-art designs, these filters have the advantages of explicit design process, quantified analysis, and multifunctional responses.

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.

Dual‐band, dual‐polarized, and compact frequency selective surface

In this article, a compact, dual-band, dual-polarized band pass single-layered frequency selective surface (FSS) structure with stable performance in wide incident angles is designed and fabricated. This structure is designed with a new proposed approach which is the combination of miniaturized-element band stop FSS and high pass grid FSS. For this purpose, a new compact band stop structure is introduced and miniaturized by adding vertical metalized holes (vias) in the substrate as additional capacitive. A WLAN band stop FSS is designed also as an example of the proposed miniaturized-element. Then, this band stop FSS is combined with a simple high pass grid structure to design the proposed band pass FSS. The circuit models of these FSSs are also extracted to achieve better description of the structures and combination idea. The dimensions of the final designed compact band pass FSS structure is 0.048λ × 0.048λ where λ is the free space wavelength of the first resonance frequency. The fabrication results of this FSS which works at WLAN bands are in good agreement with the simulation ones which prove the design approach.

Compact Microwave and Millimeter-Wave Bandpass Filters Using LTCC-Based Hybrid Lumped and Distributed Resonators

A novel class of low-temperature cofired ceramic (LTCC) bandpass filters (BPFs) is proposed in this paper, featuring of compact size and good filtering responses in both microwave and millimeter-wave (mm-wave) bands. By effectively merging the lumped elements and distributed effects, a modified LTCC-based hybrid lumped and distributed resonator (HLDR) is introduced. In detail, the lumped part of a LTCC interdigital capacitor and a high-impedance line is used to reduce circuit size, loss, and cross-talks. The distributed part, saying, the mutual couplings between adjacent HLDRs and to the ground, is used to improve the design flexibility and filtering performance for HLDR filters. With mutual couplings, the coupling matrix method can be applied. Furthermore, the frequency-variant mixed couplings between HLDRs are investigated, and coupling matrix method is improved by introducing a new coupling mechanism. Multiple transmission zeroes (TZs) are firstly realized with second-order in-line topology, but without adding cross-couplings or bandstop structures. To validate above design strategies, one S-band and one Ka-band second-order HLDR BPFs are simulated and measured, respectively. Very compact size, low loss, high-selectivity, and wide upper stopband are observed, especially in mm-wave range.

Low-RCS Reflectarray With Phase Controllable Absorptive Frequency-Selective Reflector

This paper presents a methodology to control the reflection phase response from a 3-D bandstop structure backed with an absorbing material. An absorptive frequency-selective reflection structure using the cascaded arc-shaped strip resonators and absorbers is utilized to obtain an absorption–reflection–absorption response. The reflection phase response of the structure within the reflection band is then flexibly controlled by top-loaded metallic patches with variable size. An application of this methodology is demonstrated by designing a high-gain and low-radar cross section (RCS) reflectarray. The in-band phase profile of the reflecting surface is constructively designed to collimate the beam in the far field. Meanwhile, the out-of-band scattering from the planar reflector is significantly reduced. Compared with a conventional reflectarray, the radiation performance of the proposed antenna is maintained with an aperture efficiency of 50.1% and directivity of 23.5 dBi. Significant RCS reduction has been achieved with a fractional bandwidth of 76.9% and 17.1% for the lower and upper bands with reduction levels of 10 and 8 dB, respectively.

Frequency splitter based on spoof surface plasmon polariton transmission lines

We propose a frequency splitter based on spoof surface plasmon polariton (SSPP) transmission lines (TLs). The device consists of two bent domino SSPP TLs with different geometric parameters, leading to different passbands, forming two frequency band branches. A transition from a rectangular waveguide to the two SSPP TLs is designed for frequency splitting. To achieve efficient transition for both branches in their respective frequency bands, different transition lengths of the two branches and a shifted placement from the center are adopted. Furthermore, for the high frequency band branch, to obtain satisfactory out-of-band rejection below the lower cut-off frequency, an SSPP bandstop structure is introduced by placing SSPP TL sections along the main SSPP TL. A prototype is designed, fabricated, and evaluated. The results prove the feasibility of the proposed SSPP frequency splitter.

A general strategy to fabricate photonic crystal heterostructure with Programmed photonic stopband

In this paper, we present a general fabrication strategy to achieve the structure control and the flexible photonic stop band regulation of (2+1) D photonic crystal heterostructures (PCHs) by layer-by-layer depositing the annealed colloidal crystal monolayers of different sphere size. The optical properties of the resulting (2+1) DPCHs with different lattice constants were systematically studied and a universal photonic stopband variation rule was proposed, which makes it possible to program any kind of stopband structure as required, such as dual- or multi-stopbands PCH and ultra-wide stopband PCH. Furthermore, PCH with dual-stopbands overlapping the excitation wavelength (E) and emission wavelength(F) of Ru complex was fabricated by finely manipulating the spheres’ diameter of colloidal monolayers. And an additional 2-fold fluorescence enhancement in comparison to that on the single stopband sample was achieved. This strategy affords new opportunities for delicate engineering the photonic behaviour of PCH, and also is of great significance for the practical application based on their bandgap property.

A Novel Single-Diode Microwave Rectifier With a Series Band-Stop Structure

A single-diode compact microwave rectifier with a series band-stop structure is presented in this paper. The band-stop structure is connected to the diode in series to block the harmonics produced during rectifying. It replaces the cascading bandpass or low-pass filter between the input and the diode in a conventional microwave rectifier. A microwave rectifier at 2.45 GHz with an HSMS 282 Schottky diode is realized based on the proposed design method. A short-ended eighth-wavelength microstrip transmission line is applied to the rectifier in series with the diode as a band-stop structure. The short-ended microstrip transmission line presents an inductive impedance to compensate the diode capacitive impedance at fundamental frequency and turns to an open circuit to block the second harmonic for power recycling. The proposed circuit shows a novel schematic for compact microwave rectifiers. The fabricated rectifier is compact with a dimension of $0.15\lambda _{g} \times 0.2\lambda _{g}$ . A microwave-to-dc conversion efficiency of 80.9% is achieved at 20 dBm input power with a 580- $\Omega $ dc load.

Design of Compact Wide Stopband Microstrip Low-pass Filter using T-shaped Resonator

In this letter, a compact microstrip low-pass filter (LPF) using T-shaped resonator with wide stopband is presented. The proposed LPF has capability to remove the eighth harmonic and a low insertion loss of 0.12 dB. The bandstop structure using stepped impendence resonator and two open-circuit stubs are used to design a wide stopband with attenuation level better than −20 dB from 3.08 up to 22 GHz. The proposed filter with −3-dB cutoff frequency of 2.68 GHz has been designed, fabricated, and measured. The operating of the LPF is investigated based on equivalent circuit model. Simulation results are verified by measurement results and excellent agreement between them is observed.

Double stop-band structure near half-integer tunes in high-intensity rings

Experiments at a table-top ion trap reveal space-charge driven coherent betatron resonances which will occur in high-intensity storage rings.