Design of Reactive Combiners with Enhanced Graceful Degradation

This paper shows that the electromagnetic design of rotationally symmetric reactive combiners for SSPAs requires the simultaneous optimization of the output-port reflection coefficient, the input-port return losses, and the inter-port coupling network. Minimal output reflection under symmetry maximizes the nominal combining efficiency, defined for identical MMICs. Under single-device failure, efficiency degradation scales inversely with input-port return loss, asymptotically approaching the behaviour of ideal BFN-type combiners. Failure conditions also force residual un-combined power to reappear at the active input ports, imposing additional RF stress on the surviving MMICs and necessitating isolators with suitable power-handling capability. Optimal robustness is achieved when the combiner provides uniform redistribution of the incoming power across all remaining ports.