Tunable Bandstop HMSIW Filter With Flexible Center Frequency and Bandwidth Using Liquid Crystal

Abstract

This paper reports on a tunable bandstop filter (BSF) with both flexible center frequency and bandwidth. The tunable BSF is based on half-mode substrate integrated waveguide (HMSIW), of which the broadside is coupled with reconfigurable resonators. Using liquid crystal (LC) material as the substrate, a tunable stopband could be obtained by adjusting the bias voltage of the interdigitated microstrip resonator on LC. In order to increase the tunable range of stopband bandwidth, two additional open resonators are implemented at the broadside of HMSIW cavity. For practical validation, the bandstop HMSIW filter using LC is designed and fabricated. Numerical results demonstrate that,by adjusting the voltages of three resonators on LC, either the lower or the higher cutoff frequency could be controlled independently, leading to the flexible and independent tuning ranges of both center frequency from 4.9 to 5.4 GHz and 3-dB bandwidth of stopband from 1.2 to 1.8 GHz (@5.1 GHz). INDEX TERMS Bandstop filter (BSF), half-mode substrate integrated waveguide (HMSIW), liquid crystal (LC), tunable filter.

A Compact Reconfigurable 1-D Periodic Structure in GaAs MMIC With Stopband Switching, Dual-Band Operation and Tuning Capabilities

“…In addition to these multiple adaptive features, the circuit also offers excellent rejection in the stopband, i.e., up to 55 dB, which is at least 20 dB deeper than other reported circuit topologies [3], [6], [9], [10], [12]- [15], [35], [39], [40]. Moreover, the proposed structure offers wider tuning ranges in resonant frequency and stop bandwidth for both bands, as compared to [9], [12], [13], [15], [35]. These features make the proposed structure a better choice for the reconfigurable filter design.…”

“…For example, the bandstop filter in [11] supports single-band operation with centre frequency tuning in a wide range and stopband rejection level up to 30 dB. In contrast, the filters in [12], [13] offer bandwidth tuning along with frequency tuning with lesser stopband rejections up to 20 dB. Similarly, the filters in [6], [14] demonstrate dual bandstop performance with frequency tuning, and the filter in [15] offers a dual-band operation with bandwidth tuning.…”

Novel Selective Feeding Scheme Integrated With SPDT Switches for a Reconfigurable Bandpass-to-Bandstop Filter

“…Therefore recently, reconfigurable filters have become an essential component in wireless systems and have attracted a lot of attention. Even though tunable single and multiband filtering components have been proposed [14][15][16][17][18][19][20][21][22][23][24] with a number of advantages, they usually serve a single purpose (either tunable BPF or tunable BSF). Few researchers [25][26][27][28][29][30][31][32] have presented fully reconfigurable filtering circuits exhibiting BPF-to-BSF switching capability.…”

Frequency-reconfigurable wideband bandstop filter using varactor-based dual-slotted defected ground structure

“…In [19], a tunable microstrip bandstop resonator with a C-shaped DGS was proposed, where varactors were embedded to the resonator cell and a 13% tuning range centered at 2.36 or 2.67 GHz is achieved. Some new technologies are used in the reconfigurable stopband filter [20,21,22,23]. In [20], a tunable BSF based on a half-mode substrate integrated waveguide (HMSIW) was proposed, where reconfigurability was obtained by adjusting the bias voltage of multiple interdigitated microstrip resonators on liquid crystal material.…”

“…Some new technologies are used in the reconfigurable stopband filter [20,21,22,23]. In [20], a tunable BSF based on a half-mode substrate integrated waveguide (HMSIW) was proposed, where reconfigurability was obtained by adjusting the bias voltage of multiple interdigitated microstrip resonators on liquid crystal material. However, the fractional bandwidth of only about 10% and a slow response time might limit its applications.…”