Inductive Tuned High Isolation RF MEMS Capacitive Shunt Switches

This work attempts inductive tuning of Radio Frequency Micro Electro Mechanical (RF MEM) capacitive switches for independent operation in X and Ku bands. The usual isolation characteristics of MEMS switches show wide bandwidth and moderate isolation of around 30 dB. Inductive tuning increases switch beam inductance by a few tens of pico henries. This enhances the Q factor and has the effect of improving the isolation and reducing the bandwidth of the switches. Inductive tuning is achieved by creating notches in the coplanar waveguide (CPW) ground plane in close proximity to the membrane. Membrane inductance enhancement can also be achieved by employing folded suspension beams. Since the current is concentrated on the edges of the signal and ground plane, the part of the beam over the CPW gap will have a dominating effect over the beam inductance. Beam inductance can be extracted from the simulated isolation characteristics of the switch by curve fitting. This paper presents tuning of two different rectangular coil suspension beam geometries to improve the isolation characteristics in the respective bands of frequencies.