This paper describes amplification with improved linearity by employing a linearizing circuit in an input circuit of an internally-matched Ku-band high power amplifier. The linearizing circuit is composed of series L, C, R and an FET with grounded source and drain, and is connected between the input signal line and ground. This linearizing circuit was applied to a Ku-band 10 W output power amplifier utilizing a 25.2 mm gate-width double-doped Heterojunction FET. The power amplifier demonstrated a 8 dB reduction of the third-order intermodulation at about 6 dB output power backoff point from the 2 dB output compression point.

A buried gate AlGaAs/InGaAs heterojunction FET (HJFET) with gate breakdown voltage of 30 V was examined for high drain bias (higher than 10 V) operation. High breakdown voltage was realized due to the optimization of the narrow recess depth. A 1.4 mm HJFET has exhibited an output power of 30.2 dBm (1050 mW) with 50% power added efficiency (PAE) and 12.1 dB linear gain at 12 GHz with a 13 V drain bias. An internal matching circuit for a 16.8 mm HJFET was designed using a large-signal load impedance determined from load-pull measurement. The 16.8 mm internally-matched HJFET has delivered 38.9 dBm (7.8 W) output power with 46% PAE and 11.6 dB linear gain at 12 GHz with a drain bias of 13 V. This is the first report of higher than 10 V operation of an X- and Ku-band power HJFET with the excellent power performance.