  Cavity combiners have been put forward for high power combining due to their
advantages of larger combining ability, variable input channels and less power
loss. For a high power cavity combiner, it is better to keep the power loss
ratio in a reasonable range, because large power loss would lead to strict
requirements on the cooling system. A combiner with variable input channels is
convenient for outputting different power levels according to practical
demands. In this paper, a method for designing a variable-channel high-power
cavity combiner is proposed, based on the relation between input and output
coupling coefficients obtained by analyzing the equivalent circuit of the
cavity combiner. This method can put the designed cavity combiner in a matching
state and keep its power loss rate in a reasonable range as the number of input
channels changes. As an example, a cavity combiner with 500 MHz and variable
input channels from 16 to 64 is designed, and the simulation results show that
our proposed method is feasible.
