An electromagnetic energy delivery system includes a set of radio frequency channels. Each channel includes a radio frequency feed, at least one high-power amplifier and a phase-shifting component. Each high-power radio frequency amplifier includes at least one amplifying component configured to output a periodic signal that is amplified in power with respect to an input radio frequency common reference signal. The phase-shifting component is configured to modulate the phase of the output periodic signal with respect to the input radio frequency signal. A controller coupled to the set of radio frequency channels can be configured to cause the output periodic signals from each of the radio frequency channels is to have a time-varying phase difference relative to the common reference signal and a phase difference relative to the other output periodic signals that is constant when averaged over time.