A Millimeter-wave Tunable Filter Using MEMS Varactors

A mm-wave tunable 3-pole filter was developed using high-Q MEMS varactors on a quartz substrate using a coplanar-waveguide (CPW) implementation. The measured tuning range was 23.8 GHz (0 V) to 22.6 GHz (15 V) with an associated insertion loss of -2.8 dB to -3.8 dB, and a return loss better than -12 dB over the entire tuning range. The measured 1-dB bandwidth was 8.4% at 23.8 GHz and 6.6% at 22.6 GHz. The extracted capacitance change in the analog MEMS varactors is 1.20. These numbers represent the best results achieved to-date for tunable filters. A larger tuning range can be obtained with the new of high-capacitance ratio varactors (2:1).