In this paper, a compact bandpass filter with improved band stop and band pass characteristics for wireless applications is built with four internal conductive poles in a single resonating cavity, which adds novel quad-resonating modes to the realization of band pass filter. This paper covers the design and testing of the S-band combline coaxial cavity filter which is beneficial in efficient filtering functions in wireless communication system design. The metallic cavity high Q coaxial resonators have the advantages of narrowband, low loss, better selectivity and high potential for power handling, as compared to microstrip filter in the application to determine the quality factor of motor oils. Furthermore, the tuning of coupling screws in the combline filter allows in frequency and bandwidth adjustments. An impedance bandwidth of 500 MHz (fractional bandwidth of 12.8%) has been achieved with an insertion loss of less than 2.5 dB and return loss of 18 dB at the resonant frequency. Four-pole resonating cavity filters have been developed with the center frequency of 4.5 GHz. Insert loss at 0 dB and estimated bandwidth at 850 MHz and a quality factor of 4.3 for the band pass frequencies between 4 and 8 GHz is seen in the simulated result.

Design and Synthesis of Multi-Mode Bandpass Filter for Wireless Applications

Yunping Qi(祁云平)1,† Baohe Zhang(张宝和)1, Jinghui Ding(丁京徽)1, Ting Zhang(张婷)1, Xiangxian Wang(王向贤)2, and Zao Yi(易早)3 1College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China 2School of Science, Lanzhou University of Technology, Lanzhou 730050, China 3Joint Laboratory for Extreme Conditions Matter Properties, Southwest University of Science and Technology, Mianyang 621900, China

Efficient manipulation of terahertz waves by multi-bit coding metasurfaces and further applications of such metasurfaces

A novel dual-polarized frequency-selective polarization converter (FSPC) with low-backward scattering is proposed by combining a bandpass frequency-selective surface (FSS) with a polarization converter. The FSPC, comprised of the top polarization conversion layer and the bottom multilayer bandpass FSS, is formed by introducing two polarization converter bands on both sides of the broadband passband. The four-port equivalent circuit model cascading FSS and polarization converter is proposed and investigated. It is numerically demonstrated that a flat 1 dB transmission window can be obtained from 8.5 to 11 GHz with a 25.6% fractional bandwidth (FBW), and the bandwidth of reflection below −10 dB is up to 92% from 5.6 to 15.13 GHz. Moreover, the proposed device can achieve two polarization conversion bands (5.66–6.9 and 12.8–15.2 GHz) with the polarization conversion ratio over 90%. Besides, by arranging the proposed structure in a checkerboard-like distribution, the backward scattering energy can be reduced in a wide frequency band ranging from 4.5 to 16 GHz. Both simulation and experimental results are in good agreement, which demonstrates our design strategy. Compared with the conventional polarization converters, the proposed design presents an extra frequency-selective performance and, hence, can be a great substitute for the frequency-selective rasorber (FSR).

A Multifunctional Frequency-Selective Polarization Converter for Broadband Backward-Scattering Reduction

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.

https://www.mdpi.com/2079-9292/8/11/1316/pdf

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

In this paper, a stub-loaded square ring resonator (SLSRR) is analyzed and applied to design a very simple and compact wideband bandpass filter structure. Resonant modes dependent on the structure parameters of the SLSRR are analyzed first, and then the first two modes are used to achieve a required passband. The input and output terminals are supplied with high impedance and strong coupling to provide sufficient coupling energy. Two wideband filter examples are designed, manufactured, and measured using the SLSRRs. The first filter is a wideband filter with a wide upper stopband, and the second filter is a dual wideband filter with a notched stopband between two passbands. The two filter examples are designed, fabricated, and measured to verify the design concept and present the advantages of easy design and a simple and compact structure.

https://www.mdpi.com/2079-9292/9/1/176/pdf

Application of a Stub-Loaded Square Ring Resonator for Wideband Bandpass Filter Design

In this paper, a novel composite metasurface (MS) with diffuse scattering and absorbing characteristics is proposed to reduce the radar cross section (RCS) of a metal target in a broad band. The combination of absorption and diffusion is realized based on lossy Pancharatnam-Berry (PB) phase particles. The units are arranged according to a coding sequence which is obtained by an optimization algorithm based on simulated annealing algorithm. Simulation results show that the MS obtained based on the optimized coding sequence is insensitive to polarization. Due to the combination of absorption and diffusion, the MS has good performance in both monostatic and bistatic scenarios. Finally, the proposed MS is fabricated and measured, and the experimental results are in good agreement with simulation results. A 10 dB backward reflection reduction can be achieved from 21GHz to 38GHz and a 15 dB backward reflection reduction can be achieved from 22GHz to 35GHz under normal incidence. Furthermore, the MS has good performance under large angle (<45°) incidence.

Broadband, polarization insensitive low-scattering metasurface based on lossy Pancharatnam-Berry phase particles.

In this paper, a metasurface-based antenna array with wideband radiation and broadband radar cross section (RCS) reduction is constructed. Without introducing additional radiators, the broadband radiation performance of the antenna array is achieved by inspiring the metasurface itself. In addition, the characteristic mode theory is introduced to analyze the radiation mechanism of the radiator elements and the proposed antenna array. Both simulations and measurements are carried out to verify the performance of the proposed antenna array. The results show that the impedance bandwidth and 3-dB gain bandwidth of the proposed antenna array are 5.1-9.0 GHz and 5.1-8.0 GHz, respectively, with a peak gain of 12.1 dBi. Monostatic RCS reduction more than 10 dB is achieved within the frequency band of 6.0-26.2 GHz.

A Broadband Metasurface Antenna Array with Ultra-Wideband RCS Reduction

This paper presents a simple split ring resonator excitation to realize a multi-mode wideband bandpass filter in a rectangular waveguide cavity. The proposed resonator employs two rectangular split rings attached with two coaxial probes extended into the cavity to excite two resonant modes, unlike the conventional cavity resonators which employ conductive cylinders in the cavities to achieve the same results. A hybrid magnetic (HM) mode and a hybrid electric (HE) mode are the two hybrid modes excited to realize the wideband bandpass filter. The filter operates at 2.5 GHz center frequency with 53% fractional bandwidth. Finally, the prototypes of a second and a fourth order filter are fabricated for results validation. Measured results are in good agreement with the simulated ones.

Multiple-Mode Wideband Bandpass Filter Using Split Ring Resonators in a Rectangular Waveguide Cavity

This paper proposes a method for designing a quadruple-mode wideband bandpass filter using off-centered perturbed metallic cylinders in a rectangular waveguide cavity with compact size and improved out-of-band rejection. Two off-centered perturbation cylinders were placed at the bottom of the rectangular waveguide cavity along with a pair of perpendicularly-fed coaxial lines, which excited four quasi-transverse magnetic (TM) modes to realize the desired passband. The height of the waveguide cavity and the shape of the perturbation cylinders were exploited to achieve an all quasi-TM modes filter with good out-of-band rejection and sharp skirt selectivity. The proposed filter operates at 2.93 GHz center frequency with 38% wide fractional bandwidth (FBW). The proposed filter is fabricated using aluminum. The measured and simulated results are in good agreement with each other.

https://www.mdpi.com/2079-9292/8/3/300/pdf

Quadruple-Mode Wideband Bandpass Filter with Improved Out-of-Band Rejection

This paper presents a simple perturbation technique using an off-centered metal cylinder in rectangular waveguide cavity to realize a triple-mode wideband bandpass filter. A TM mode along w...

Lina Qiu

Papers

Broadband, polarization insensitive low-scattering metasurface based on lossy Pancharatnam-Berry phase particles.

A Broadband Metasurface Antenna Array with Ultra-Wideband RCS Reduction

Multiple-Mode Wideband Bandpass Filter Using Split Ring Resonators in a Rectangular Waveguide Cavity

Quadruple-Mode Wideband Bandpass Filter with Improved Out-of-Band Rejection

Triple-mode wideband bandpass filter using simple perturbation in metallic-loaded rectangular waveguide cavity