Gallium Nitride Microwave Transistor Technology for Radar Applications | January 17, 2008

This article reviews the relative merits of silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC) and gallium nitride (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.

From: Vol. 51 | No. 1 | January 2008 | Page 106

by Aethercomm

Many microwave radar transmitters require active devices that 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, semiconductor transistors have up until recently 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.¹ High-current operation is inefficient due to series losses and the fact that large-area devices have inherently high capacitance and very low impedance, which limit operating frequency and bandwidth.¹ GaN technology now offers a solution to this dilemma.

Solid-state amplifiers are already replacing traveling-wave-tube amplifiers (TWTA) for a variety of microwave power applications. However, the low operating voltages of Si and GaAs devices lead to a large device periphery, resulting in high device and circuit complexity and reducing production yield and reliability. Wide bandgap technologies like GaN can achieve a power density five times higher than that of conventional GaAs-based metal-semiconductor field effect transistors (MESFET) and heterojunction bipolar transistors (HBT). This will ultimately result in reduced circuit complexity, improved gain and efficiency and higher reliability. In particular, radar systems will benefit from the development of this technology.

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