Optimization of out-of-band impedance environment for linearity improvements of microwave power transistors

Abstract

This paper introduces a novel method that allows the presentation of specific, broadband impedances to a DUT by loadpull. To investigate this method, a derivative of class J power amplifier termed BJ is emulated, which effectively lies between class J and class B along the reactive routes on the Smith chart. The mode helps explore baseband linearization approach and its suitability when using continuous mode architectures. Adopting out-of-band impedance optimization technique allows to present impedances and move progressively from a completely real set of loads to completely imaginary set of loads in a deterministic and systematic way. This further extends a view to look at how well the emulated mode linearizes at a set of BJ contour points along the way. The method uses multiple modulated signal sources, phase synchronized at both radio frequency (RF) and intermediate frequency (IF) to provide a complete multi-harmonic broadband loadpull capability controlled by a single local oscillator and allows complete impedance control at the DUT current generator plane.