X-Band High Power GaN SPDT Switch MMIC for Space based Radar Front End

This paper presents the design and realization of a X-Band GaN HEMT based high-power Single Pole Double Throw (SPDT) switch for a space based phased array RADAR front ends. The switch is designed using the space qualified 0.25um GaN-on-SiC process of United Monolithic Semiconductors. The switch is designed using series-shunt configuration and its performance is measured and evaluated over the frequency band of 9 GHz – 11 GHz. and fits in a size of 1.3mm X 1.79mm. The switch exhibits state-of-art performance with an insertion loss of less than 0.85dB, isolation> 25 dB and on-state power handling capability of better than 42 dBm at 0.5 dB insertion loss compression point. The input return loss is better than 20dB and the output return loss of both the on and off states are better than 17dB over the entire bandwidth.

I. Introduction

Microwave switches are an essential component in communication and phased array radar systems which require switching of an RF signal from one path to another. They are widely used in transmit/receive modules with a common antenna for switching transmit/receive path and also in digital phase shifters and digital attenuators for selecting reference path and phase shifting/ attenuating path. Traditionally, the microwave switches are designed using PIN diode because of its low loss and high switching speed. However, PIN diode is a current-driven device and hence it typically requires a complex DC bias circuitry and consumes a significant amount of DC power. In contrast to this, a Field Effect Transistor (FET) is a voltage-driven device and consumes much less power [1]. A GaAs FET-based switch requires a simpler voltage controlled bias network and draws nearly zero quiescent DC current but has a lower breakdown voltage which results in low power handling capability. This can be overcome by using GaN technology which provides an order-of-magnitude increase in power handling due to its wide bandgap properties [2]. In the last few years, the advances in this technology has demonstrated it to be ideal for high frequency and high power MMIC design applications.