An Enhanced Modulated Waveform Measurement System

Abstract

Microwave power transistors used in modern day wireless communication systems need to be characterised under complex modulated excitations into variable load impedances for the determination of optimum matching conditions. This paper presents a refined modulated waveform measurement system for the robust characterisation and optimisation of non-linear microwave devices when driven by broadband multi-tone stimuli. This enhanced system has the ability to present specific, constant broadband impedances, not only at baseband frequency, but also at radio frequencies, particularly, around the carrier and significant harmonics. Achieving such comprehensive impedance control across wide modulation bandwidths is critical in allowing the emulation of new power amplifier modes and architectures, and the subsequent waveform characterisation of devices operating in these complex and often dynamic impedance environments. The capability of the enhanced system is experimentally demonstrated through the measured adjacent channel intermodulation power behaviour of a 10 W GaN HEMT biased in class AB and tuned for maximum output peak envelope power.