An X-band internally-matched GaN HEMT amplifier with compact quasi-lumped-element harmonic-terminating network

A compact quasi-lumped-element resonator is proposed as a harmonic-terminating network for internally-matched amplifiers. It is a parallel connection of an inter-digital capacitor and a transmission line, and its compactness is suitable for packaged internally-matched FET amplifiers. An X-band internally-matched GaN HEMT amplifier has been fabricated, in which the proposed harmonic-terminating network is used at the input of the HEMT for realizing an optimum 2^nd-harmonic input impedance seen from the HEMT to maximize power-added efficiency (PAE). In measurements, PAE of 50 % with output power of more than 18 W has been obtained in a moderate bandwidth of 10 %.