A Miniaturized and Compact Reconfigurable Low-Pass Filter

This paper presents a compact reconfigurable low-pass filter (LPF). Through analysis of the LPF circuit structure and its transmission zero characteristics, a varactor diode is loaded at the first transmission zero position to enable frequency tuning of the transmission zero point, thereby achieving adjustable cutoff frequency of the low-pass filter. The proposed reconfigurable LPF features a simple tuning mechanism that requires only one varactor diode controlled by reverse bias voltage. Experimental results demonstrate that the 3-dB cutoff frequency of this reconfigurable LPF achieves a tuning range of 60% (0.75-1.4 GHz). Within this tuning range, the filter exhibits excellent performance: insertion loss better than 0.8 dB, return loss better than 16 dB, and a maximum roll-off rate reaching 66.7 dB/GHz.