Filter-less diplexer enables active harmonic load-pull at ka band

As circuit element losses increase with frequency and availability of power amplifiers reduces also, active control of harmonics by means of a traditional filter and hybrid diplexer becomes problematic. In this paper a technique is presented that allows the reflective filters to be removed, and lower loss couplers to be used, resulting in much less power being needed to control the second harmonic, and also a useful reduction in the fundamental load-pull power. The effectiveness of the method is demonstrated using a GaN based HEMT device, and then some of the extensions possible are presented.