A switching combiner unit (SCU) may combine coherent RF or
microwave outputs from multiple power
amplifier units (PAUs). Each SCU may be able to be switched between an on-line mode (on-line PAU), during which the PAU amplifies a coherent instance of the same RF or
microwave input
signal and delivers that amplified input
signal to an output, and a standby or off-line mode (standby / off-line PAU), during which the PAU does not amplify an instance of the same RF or
microwave input
signal or deliver an amplified input signal to the output. The SCU may include an input port that connects to each of the PAU outputs; a
control signal input that receives one or more control signals that indicate whether each PAU is in the on-line or standby / off-line mode; signal combining circuitry that coherently sums the outputs from all of the on-line PAUs, while simultaneously isolating the standby / off-line PAUs from the output of the SCU and the outputs of the on-line PAUs; and an SCU output port that delivers the coherently summed outputs from all of the on-line PAUs.