A Novel Frequency and Bandwidth Tunable $L C$ Bandpass Filter with Two Transmission Zeros
Shanfu Zhou, Qianyin Xiang, Longchuan Liu, Quanyuan Feng · 2025
This paper presents a novel mixed-coupled LC bandpass filter (BPF) that allows for independent adjustment of both the −3 dB bandwidth and the center frequency. The filter exploits transmission zeros (TZs) generated by the mixedcoupling structure and those produced by the LLC-tuned branch, which functions independently. This innovative design facilitates the separate tuning of the center frequency and the −3 dB bandwidth. Experimental results demonstrate that the designed filter achieves a center frequency tuning range from 200 MHz to$\mathbf{4 2 0 M H z}$, with a maximum$-\mathbf{3 d B}$bandwidth of at least$\mathbf{4 0 M H z}$at each center frequency. Furthermore, the −3 dB bandwidth can be tuned over a range exceeding 10 MHz.