Abstract: A radio frequency (RF) carrier wave is successively divided and the divided parts are non-linearly, phase modulated in response to a modulating signal. The modulating signal is linearized so that the output of the circuit is linear with the modulating signal and then drives differential drivers to control voltage controlled phase shifters in pairs to differentially phase shift the divided RF signals. These phase shifted signals may be efficiently amplified in non-linear, Class C, RF power amplifiers. After amplification the signals are differentially re-combined in an inverse binary tree of hybrid combiners to produce a synthesis output signal. This synthesis output signal is equivalent to the amplitude modulation, and the amplification, of the RF input signal. By operation of the circuit apparatus in accordance with the invention, amplitude modulation at wide bandwidths including hundreds of megahertz may typically be accomplished on microwave RF signals of high power levels including several kilowatts.