Design considerations for X-band Class J power amplifiers

The design considerations for Class J power amplifiers at high RF and microwave operating frequencies were investigated through the design of an X-band Class J Power Amplifier (P A) based on an off-the-shelf, high power, discrete GaN HEMT. The end-to-end design process had been studied, beginning with the derivation of the device-specific Class J design space up to the design of the over-all Class J circuit with provisions for third harmonic control and load harmonic filtering. The design goal was to simultaneously maximize output power, efficiency, and bandwidth, yielding a design for a 6-W Class J final-stage PA with an operating frequency of 9.2–10.8 GHz, > 50% drain efficiency, and 8.1 dB gain. Through the investigation of the design process, the study is able to give perspective on the achievable performance from Class J at the X-band, thereby promoting further study on efficient broadband communications at high RF and microwave frequencies.