Abstract: A substantially constant power level is derived over a predetermined frequency band, in each of a plurality of relatively widely spaced power ranges, from a microwave load having a predetermined amplitude versus frequency response, such as an antenna. A microwave source of substantially constant amplitude drives a forward path connected between the source and the load. The forward path includes a voltage controlled, PIN diode, variable microwave attenuator. A feedback path responsive to the microwave power level in the forward path derives a control voltage for the PIN attenuator. The feedback path includes a microwave equalizer attenuator having an amplitude versus frequency response corresponding substantially with the amplitude versus frequency response of the load. The equalizer attenuator drives a linear, crystal amplitude detector.