A 25-75-MHz RF MEMS tunable filter

This paper presents a state-of-the-art discrete RF microelectromechanical systems (MEMS) tunable filter designed for 25-75-MHz operation. This paper also presents an enhanced model of the RF MEMS switch, which is used for accurate prediction of the tunable filter response. The two-pole lumped-element filter is based oil digital capacitor banks with on-chip metal-contact RF MEMS switches and lumped inductors, and results in a tuning range of 3 : 1 with fine frequency resolution, and a return loss better than 13 dB for the entire tuning range. The relative bandwidth of the filter is 4 [+ or -] 1% over the tuning range and the insertion loss is 3-5 dB, limited mostly by the inductor Q and the switch loss. The II[P.sub.3] measurements prove that tunable filters with metal-contact series RF MEMS switches show extremely linear behavior (II[P.sub.3] > 68 dBm). Index Terms--Microelectromechanical systems (MEMS), RF MEMS, tunable filters.