High-Selective Bandpass Filters Based on New Dual-Mode Rectangular Strip Patch Resonators
Qing Liu, Dongfang Zhou, Xian Wang, Min Tang, Dewei Zhang, Yi Zhang
Abstract
The resonant characteristic of rectangular strip patch resonator (RSPR) is studied in detail, and a new dual-mode resonator based on TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">020</sub> modes is proposed to design bandpass filters (BPFs). A two-pole BPF with two finite transmission zeros (FTZs) based on one nondegenerate dual-mode RSPR is presented and analyzed. And then, a four-pole BPF with four FTZs based on two cascaded nondegenerate dual-mode RSPRs is proposed. The two dual-mode RSPRs are connected directly by a quarter wavelength strip-line. Finally, a four-pole BPF with the center frequency of 5.8 GHz is designed, fabricated, and measured. The measured insertion loss in center frequency, 1-dB bandwidth, and return loss are 1.45 dB, 206 MHz, and 12.85 dB, respectively. Measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor is about 315.