A 2-pole digitally tunable filter using local one bit varactors

This paper presents the design of tunable filters based on capacitive RF MEMS switched loads appropriately distributed along an hairpin resonator. The capacitive load distribution is computed using hybrid circuit EM simulation and allows precise computation of the frequency shift for every location of the switched load. To prove the concept, a two pole filter has been fabricated on a 525 mum-thick quartz substrate and it occupies a total area of 1 times 0.85 cm². Its center frequency can be discretely tuned using 2 capacitive switches from 9.8 to 11 GHz with 4 positions. Return losses less than 15 dB and insertion losses better than 2.5 dB have been measured over the whole operation band.