500W Long-Pulse High Efficiency UHF BJT Transistor for Radar Applications

A 500 W very long-pulse high efficiency BJT power transistor is presented, which operates at 6 mS pulse width, 20% duty cycle and 36 V supply voltage. The output power exceeds 500 Watts; the efficiency is higher than 60%; and power gain is greater than 11dB across 400 MHz to 450 MHz. The die layout, internal impedance matching technique and external impedance matching of the test fixture design is also described. The thermal resistance is 0.25C/W. The junction temperature remains below 150 C at the heat sink temperature of 70 C. This transistor uses state-of-the-art silicon BJT technology in a common emitter configuration and class C operation. This combination of high power, long-pulse, and high efficiency makes these devices ideally suited for transmitter designs in UHF radar systems.