Systematic investigation of the impact of harmonic termination in the efficiency performance of above octave bandwidth microwave amplifiers

The importance of harmonic terminations in achieving high-efficiency operation in narrow band (NB) amplifiers has been widely published. In Wide Bandwidth (WB) applications however, the emphasis has been on maintaining a broadband match at the fundamental frequencies with little regard to the harmonic impedances. The problem is further complicated by the fact that the harmonics of the lower frequencies often fall within the operational bandwidth of the amplifier. This paper presents an active load-pull technique for measuring and quantifying the impact of harmonic impedance on device performance, and is achieved through the characterisation of a class A biased 0.3 μm GaAs pHEMT ½W device at 6, 12 and 18 GHz.