Mechanically Tunable Lowpass Filter in Form of Suspended Substrate Stripline

Abstract

A mechanically tunable lowpass filter is proposed in this paper, and the main part of the filter is a suspended-substrate-stripline-based high/low impedance lowpass filter. The tunability is introduced by applying a movable lid with several metal ribs. When the lid is moving, part area of each high or low impedance section will be overlapped by corresponding rib, and the total inductance/capacitance will be tuned, resulting in a continually tunable cutoff frequency of a lowpass filter. The designed tunable lowpass filter has a tunable range of the cutoff frequency from 0.64 to 1.1 GHz. Along with the tunable cutoff frequency, the insertion loss keeps to be less than 1dB and the return loss remains better than 10 dB. The simulated and measured results, which are in good agreement, have verified the performance of the proposed filter.