Patent ID: 8103225

Claim:
A method of maintaining isolation within a multiport amplifier for a communications satellite, the multiport amplifier comprising a plurality of microwave power amplifier units, a plurality of input ports and a plurality of output ports, the input ports being connected to said amplifier units by an input signal dividing network, and the output ports being connected to said amplifier units by an output signal dividing network, so that an input signal at any input port is amplified by all amplifier units, and then recombined into an output signal at an output port, the method comprising: providing at least one of said amplifier units with gain adjusting means and phase adjusting means, providing a feedback control loop extending from a preselected node in said output signal dividing network to said gain adjusting means and phase adjusting means, injecting a pilot signal into said input signal dividing network, and detecting said pilot signal at said preselected node, so that said feedback loop provides phase and gain adjustment signals in dependence on the value of the detected pilot signal, wherein said output signal dividing network includes a first column of output hybrids, each output hybrid of the first column being connected to first and second amplifier units of said plurality of amplifier units and at least one of the first and second amplifier units having gain adjusting means and phase adjusting means, and wherein said preselected node comprises an output port of one of said output hybrids of the first column, at which a signal null of said pilot signal occurs.