Design of Reactive Combiners with Enhanced Graceful Degradation

This paper demonstrates that the electromagnetic design of rotationally symmetric reactive combiners for solid-state power amplifiers (SSPAs) with enhanced graceful degradation is governed by three key parameters: output-port return loss, inputport return loss, and inter-port coupling. While output-port return loss determines nominal combining efficiency, graceful degradation under single-device failure is governed by two factors: input-port return loss and symmetry of inter-port power redistribution. Under single-device failure conditions, efficiency degradation scales inversely with input-port return loss, asymptotically approaching the behavior of ideal beam-forming network (BFN) combiners. Failure-induced residual power is redistributed among the remaining input ports, increasing RF stress on the surviving MMICs and necessitating isolators with adequate power-handling capability. Optimal fault tolerance is achieved when power injected into any one port is uniformly redistributed among all other ports.