Design of X-band GaN combined power amplifier for radar applications

Abstract

Most wireless systems must be able to output a high enough output power to serve their purpose. A power amplifier is often needed in order to amplify the outgoing signal to a decent power level. Power amplifiers can be constructed using a variety of materials and techniques. Most modern amplifiers are constructed using semiconductor materials. Gallium nitride or GaN is a relatively recent semiconductor material used to manufacture high speed transistors that can handle high power levels and withstand high temperature. Smaller and more efficient amplifiers can be constructed if using GaN as compared to using other semiconductor materials. A surface mount 25 W GaN transistor have been used to construct a prototype of a combined power amplifier. The amplifier was supposed to use two of these transistors in a combined configuration and be able to output 50 W of power at X-band. The design was realized by simulations using a computer based design tool together with a non-linear transistor model. A prototype was then constructed to be able to perform measurements and analyze its performance. The prototype was able to output up to 50 W of power, but bandwidth and efficiency did not reach the same levels compared to when performing the simulations. Maximum performance was reached at a frequency 350 MHz lower than expected.