The S-band has long been an application space servicing both commercial and military radars. Many of the radar systems required very high peak power levels with low to medium pulse widths that were best served by silicon bipolar technology. Silicon Bipolar Junction Transistor (BJT) technology has demonstrated very high power density under pulsed conditions and established ease of use. A true measure of power density must include a very dense die delivering a very high power level in a small package footprint combined with a small matching circuit wrapped around the device. The RF power devices were biased in Class C mode of operation to maximize efficiency at maximum power with little regard for linearity which wasn’t a critical factor. The small matching circuits and simple bias circuitry make the BJT devices easy to implement into complex systems . The growing S-band market grew to demand wider bandwidths and higher power levels which were both well served with silicon BJT technology.
In the last few years the trend in radar systems requires longer pulse widths and some measure of linearity. A new technology was required to satisfy these advanced requirements. Although most MOSFET (Metal Oxide Semiconductor Field Effect Transistor) technologies would provide the functionality being sought, the simplest solution is a LDMOS (Laterally Diffused MOSFET) process which is silicon-based and therefore the most cost effective in a price sensitive market. Silicon LDMOS technology has many advantages including higher gain, better ruggedness , and is inherently more linear while running in Class AB mode of operation.