Compact, Wide Stopband, Shielded Hybrid Filter Based on Quarter-Mode Substrate Integrated Waveguide and Microstrip Line Resonators

• Published in: IEEE microwave and wireless components letters Vol. 31; no. 3; pp. 245 - 248
• Main Authors: Zheng, Yan, Zhu, Yilong, Wang, Zhan, Dong, Yuandan
• Format: Journal Article
• Language: English
• Published: IEEE 01.03.2021
• Subjects: Band-pass filters; Bandpass filters (BPFs); controllable transmission zeros (TZs); Couplings; Microstrip; microstrip resonator; Microstrip resonators; Q-factor; quarter-mode substrate integrated waveguide (QMSIW); Resonators; Substrates
• ISSN: 1531-1309; 1558-1764
• DOI: 10.1109/LMWC.2020.3049048

A novel miniaturized bandpass filter (BPF) with high stopband rejection based on a hybrid structure is proposed with shielded quarter-mode substrate integrated waveguide (QMSIW) and microstrip technologies. The shielded QMSIW cavity provides a high-quality (<inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula>) factor with substantial size reduction. This filter exhibits flexible response with four poles and two controllable transmission zeros (TZs) by incorporating two quarter-wavelength microstrip resonators into two back-to-back QMSIW resonators. The working principles for higher order mode suppression and filter coupling topology are carefully illustrated by eigen-mode simulation, coupling matrix, and field distribution analysis, respectively. Compared with the reported works, the proposed four-order BPF demonstrates advantageous features in terms of a compact size of <inline-formula> <tex-math notation="LaTeX">0.62\,\,\lambda _{0}\times 0.62 \,\,\lambda _{0} </tex-math></inline-formula>, a low insertion loss of 1.2 dB, a wide passband (22.7%), and a high stopband rejection (better than 36 dB).