Realization of Multiple Transmission Zeroes for Bandpass Filters With Simple Inline Topology

作者：Shen, Guangxu; Che, Wenquan^*; Feng, Wenjie; Wang, Chenxv

来源：IEEE Transactions on Circuits and Systems II: Express Briefs , 2020, 67(6): 1029-1033.

DOI：10.1109/TCSII.2019.2929231

• Asymmetric open stubs
• bandpass filter (BPF)
• mixed couplings
• transmission zeroes

The realization method of multiple transmission zeroes (TZs) for second-order bandpass filters (BPFs) is presented in this brief. A modified filter topology with mixed couplings is investigated at first. With the cancelation effect of electric and dominant magnetic couplings, two close-to-passband TZs can be easily realized for a second-order inline filter. Furthermore, the dual-function feature of loaded quarter-wavelength (lambda/4) resonators is analyzed. Besides of filtering response, lambda/4 resonators can be used to realize two more TZs in the stopband. At last, multiple open stubs are loaded asymmetrically at feeding lines, each of which can generate one TZ independently. Due to the asymmetric loading, the extra circuit area of bandstop structures is reduced by half. For demonstration, a wideband BPF using lambda/4 resonators and four asymmetric open stubs is designed, fabricated, and measured. The stopband suppression can be improved to 10.2 GHz without sacrificing in-band properties or enlarging circuit size. Good agreement can be observed between the measured and simulated results of the proposed BPF.

• 单位
  南京理工大学