GaN power amplifier with harmonic controlled by dual band-notched UWB bandpass filter

In this paper, a new type of GaN HEMT power amplifier (PA) using dual band-notched UWB (Ultra Wideband) bandpass filter which is proposed to control harmonic components at 2.14 GHz is designed and tested. The dual band-notched UWB bandpass filter is constructed by three hairpin fingers and two pairs of folded fingers added on both side extremities, so that it can suppress 6.42 GHz and 10.7 GHz by 16.1 dB and 20.3 dB concurrently with low insertion loss at fundamental frequency 2.14 GHz. For this amplifier, second and fourth harmonics are rejected by the bias circuit, while third and fifth harmonics are rejected by the filter. Due to the interdigital hairpin line structure of the filter, the blocking capacitor is not needed in the load matching network. Comparing with the harmonic control structure constructed by conventional λ/4 transmission line, the size of this amplifier circuit is reduced. The measured maximum PAE is 66.3% with 37.5 dBm output power at 2.14 GHz. The maximum gain is 14.7 dB.