Gallium Nitride (GaN) Microwave Transistor Technology For Radar Applications

By AetherComm

Abstract:
This paper reviews the relative merits of Si, GaAs, SiC, and GaN materials and describes how the attributes of each impact the operation of microwave transistors for the generation of high RF output power, on the order of hundreds to thousands of watts, as necessary for radar systems. It is shown that the superior physical attributes of GaN lead to microwave transistors that are extremely well suited for high power applications. The superior properties of GaN combined with modern high efficiency biasing techniques make GaN technology a prime candidate for use in transmitters for radar systems.

INTRODUCTION
Many microwave radar transmitters require active devices which can produce RF output power in the order of kilowatts to even megawatts. Routinely microwave traveling-wave tube devices are utilized for this application. However, the currently used traveling-wave tubes are inefficient, large, expensive, and have suspect reliability. While semiconductor-based amplifiers in principle can offer a more effective solution, up to recently semiconductor transistors have been limited in the DC voltage that can be applied to the device by the inherent critical breakdown field that the material can sustain. Since limited DC voltage can be applied, high RF power operation requires large DC and RF current, which in turn requires large area devices. High current operation is inefficient due to series losses and due to the fact that large area devices have inherently high capacitance and very low impedance which limit operating frequency and bandwidth. GaN technology now offers a solution to this dilemma.