Tunable interdigital coplanar filters using MEMS capacitors

This paper presents a switchable interdigital coplanar filter with tapped-line feedings using MEMS capacitors. Center frequency shift is obtained by adding a piece of line at the end of each basic resonator. The connection between these two elements is realized by MEMS capacitors used as an ON/OFF switches with a high-capacitance ratio between the two states. A two pole switchable filter has been designed, fabricated and measured. The center frequency can be discreetly tuned from 18.55 to 21.05 GHz with low return losses (about 15 dB) and low insertion losses (about 3.5 dB).