Compact UWB BPF With Broad Stopband Based on Loaded-Stub and C-Shape SIDGS Resonators

• Published in: IEEE microwave and wireless components letters Vol. 32; no. 5; pp. 383 - 386
• Main Authors: Xie, Jiacheng, Tang, Deshan, Shu, Yiyang, Luo, Xun
• Format: Journal Article
• Language: English
• Published: IEEE 01.05.2022
• Subjects: Band-pass filters; Bandpass filter (BPF); broad stopband; Integrated circuit modeling; Load modeling; Microstrip; Passband; Resonant frequency; Resonators; substrate-integrated defected ground structure (SIDGS); ultra-wideband (UWB)
• ISSN: 1531-1309; 1558-1764
• DOI: 10.1109/LMWC.2021.3136561

In this letter, two types of substrate-integrated defected ground structure (SIDGS) resonators (i.e., loaded-stub and C-shape resonators) are proposed for the ultra-wideband (UWB) bandpass filter (BPF) design. Coupled SIDGS resonators can generate four transmission poles to achieve the UWB response with low insertion loss in a compact size. Besides, the spurious cancellation with a broad stopband is achieved by mutual suppression of separated harmonics from the SIDGS resonators. In addition, the lowpass units (LPUs) embedded in the microstrip feed-lines are utilized to further improve the BPF stopband rejection. To verify the mechanism, a compact BPF operating at 6.85 GHz (i.e., the passband center frequency <inline-formula> <tex-math notation="LaTeX">f_{0} </tex-math></inline-formula>) with 0.6-dB insertion loss and 3-dB fractional bandwidth (FBW) of 114% is implemented and fabricated. The measured stopband extends to <inline-formula> <tex-math notation="LaTeX">9.7f_{0} </tex-math></inline-formula> with a rejection level more than 26 dB.