Frequency characteristic of power efficiency for 10 W/30 W-class 2GHz band GaN HEMT amplifiers with harmonic reactive terminations

An increase in amplifier efficiency is generally accompanied by a narrow bandwidth characteristic, especially when used with distributed transmission lines, since higher harmonics have to be treated. The frequency dependence of harmonic reactive terminations using transmission lines has been discussed for a high-efficiency amplifier design. In simulation, the designed amplifiers showed steep efficiency degradation due to a small source-side impedance shift for the second-order harmonic frequency. Therefore, both the source- and load-side circuits have to be optimized simultaneously. Fabricated 10-W and 30-W class GaN HEMT amplifiers including DC bias circuits exhibited a maximum drain efficiency of 81% at 1.98GHz and 77% at 1.95 GHz, respectively.