A wideband 0.7–2.2 GHz tunable power amplifier with over 64% efficiency based on high-Q second harmonic loading

A non-resistive high-Q bandwidth-extension technique for wideband high-efficiency power amplifiers is proposed in this paper. Specifically, the problem of proper termination of the second harmonic in power amplifiers with over 2:1 bandwidth is addressed. A tunable narrowband high-Q band-stop filter is included at the output of the power amplifier to properly terminate the transistor at its lower-band frequencies whose second harmonics fall within the bandwidth of the amplifier. The presented design is experimentally validated by manufacturing and measuring a 0.7-2.2 GHz GaN wideband high-efficiency power amplifier terminated by a high-Q (measured Q of 900) narrow-band (10 dB bandwidth of 2 MHz) band-stop filter tunable from 1.4-2.2 GHz. An over 3:1 bandwidth is achieved with measured output power of 40 dBm, average gain of 10 dB, and efficiency of > 64%. The proposed termination results in an average improvement of over 10% throughout the entire bandwidth.