MEMS switchable interdigital coplanar filter

This paper presents a tunable interdigital coplanar filter with tapped-line feedings. Microelectromechanical systems capacitors are used as a high contrast capacitive switch between a quarter-wavelength resonator and an open-ended stub to perform the frequency shift. A two-pole tunable filter with a 13% relative bandwidth has been designed, fabricated, and measured. The center frequency can be switched from 18.5 to 21.05 GHz with low return losses (less than 15 dB) and low insertion losses (3.5 dB).