By Brian D. Battaglia, Jeff Burger, and John Titizian, Integra Technologies, Inc.
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.
Even more recently, the market has demanded not just higher power or wider bandwidth devices, but products that reduce the design time of the complex radar systems. Due to fewer resources and more focus on system level design features, the RF portion of the system is being designed at the semiconductor vendor more and more often. Integrating several power transistors in parallel and matching the module to 50 ohms creates pallets that customers can drop-in to their systems. Combining several pallets together for any power level is straight forward and reduces the design time. Higher levels of integration have been provided by combining more than one stage cascaded together to provide a high gain pallet that offers a complete solution and eases the work load on the busy radar system design engineer.
Leveraging their long history in the S-band and RF expertise, the designers at Integra have developed another product that offers a complete 50 ohm RF power solution in a single package. Miniaturized Power Amplifiers utilizing LDMOS (MPALs) are matched to 50 ohms at the package leads and only need a bias circuit to complete the solution.