Active VSWR Robustness Comparison for Different Phase Combining Topologies

This paper presents a comparative study on the resilience to load variations brought by combining structures for amplifier topologies. Three out-of-phase four-way combining topologies based on Wilkinson combiners, 90° and 180° hybrid couplers are compared with a conventional in-phase four-way combining topology based on Wilkinson combiners. An experimental evaluation is conducted using a load-pull bench for the characterization of printed circuit board (PCB) demonstrators operating at 2.45 GHz with a VSWR up to 5:1. Measurement results point out the superiority of the out-of-phase combining topologies providing reduced performance variations under load pulling. It is demonstrated that these topologies have a higher resilience to unpredictable load variations, with reduced gain, efficiency, and output power variations. For all the considered out-of-phase combining demonstrators, the gain variation is reduced by more than 1.5 dB at 1 dB compression point compared to the conventional in-phase combining demonstrator.