A Widely Tunable RF MEMS End-coupled Filter

Abstract — A three-pole tunable end-coupled filter from 6 to 10 GHz was developed with a broad 35 % tuning range. This tuning range was realized by switching distributed loading structures with radio frequency microelectromechanical systems (RF MEMS) capacitive switches. By tuning the coupling capacitors as well as the loading capacitors, the filter achieved a constant fractional bandwidth of 15±0.3 % and an insertion loss ranging from 3.3 dB to 3.8 dB over the entire band. Digital switching ensured good thermal stability, and microstrip transmission lines provided lower insertion loss than with coplanar waveguide. Future improvements are expected to decrease the insertion loss to below 2.1 dB. Index Terms — Adaptive filters, microstrip filters, resonator filters, switched filters, tunable filters, microelectromechanical devices. I