L-Band Power MOSFET

L-Band power amplifiers for such applications as the TPS-59 phased array radar have used silicon bipolar transistors. The performance of power MOSFETs at VHF and UHF offered promise that there could be significant benefit for future L-band radars if their advantages could be extended to L-band. MOSFETs have demonstrated easier power combining and greater gain than their bipolar counterparts. FETs offer several attractive features as microwave high power devices. Bias networks are uncomplicated and FETs can be employed in a simple pulsed generator mode saving costly circuit switching elements. In contrast to the bipolar device, the drain current of the FET has a negative temperature coefficient at high current levels, therefore it has the tendency to be thermally stable and can typically withstand higher VSWR mismatches. Since the FET is a majority carrier device it exhibits lower noise floor characteristics. FETs are basically square law devices and can be expected to be more linear with smaller intermodulation and cross modulation products.