A tunable bandstop filter using T shaped DGS and MEMS switches on CPW

Abstract

In the present work, a band stop filter with tunable resonant frequency and tunable bandwidth is proposed using micro electromechanical (MEMS) switches. The band stop filter is based on defected ground structures (DGS). Tunability of resonant frequency is achieved through two methods for fine and coarse tuning. The various switching states of the filter are represented by equivalent circuit models. Four MEMS series switches are loaded over each of the four branches of a T-shaped DGS structure. The switches are successively actuated to increase the resonant frequency of the filter in narrow steps. A coarser method of tuning the resonant frequency makes use of two switches connected across the gaps of the DGS. In this method, the resonant frequency varies nonlinearly with the height of the switch beam. The bandwidth of the filter is tuned by actuation of MEMS shunt switches, forming a distributed MEMS transmission line (DMTL) in the spacing between the DGS structures. The actuation of the MEMS shunt switches in the DMTL results in a slow wave effect. This increases the effective electrical length between the DGS structures leading to increase in bandwidth.