A low insertion loss, multi-band, fixed central capacitor based RF-MEMS switch

Abstract

This paper presents a new type of capacitive shunt RF-MEMS switch. In the proposed design, switch consists of a beam in the form of two symmetric cantilevers anchored at the central conductor of CPW, where they generate a fixed capacitance, whereas the free ends of the cantilevers are hanging over the ground plane of the CPW. The net up-state capacitance thus can be approximately determined from the area of overlap between the ground plane and free ends of cantilevers rather than the central overlap area as in the case of conventional movable bridge based approach. Further, the switch is used to inductively tune the isolation peaks in C and X bands i.e. 44.53 dB at 4.5 GHz and 51.08 dB at 9.8 GHz, when either or both cantilevers are electro-statically actuated to the down-state position. The device with movable bridge has isolation peak only at a single frequency in X band. Device shows an insertion loss less than 0.15 dB, a return loss below 21.38 dB up to 25 GHz as compared to 1.00 dB insertion, 7.67 dB return loss for the equivalent conventional switch with movable bridge. In addition, improvement of around 3.5 times in the bandwidth and 50 % reduction in the pull-in voltage has also been achieved. The designed switch can be useful at device and sub-system level for the future multi-band communication applications.