A comb frequency generator that is tunable to vary the width of the pulses in the output signal and achieve a maximum power output at different harmonic frequencies. A wavefront compression device receives a sinusoidal input signal and provides wavefront compression to create a compressed signal having a series of periodic fast edges. A delay device receives the fast-edge compressed signal and delays the fast-edge signal to create a delayed fast-edge signal. A combining device receives the original fast-edge compressed signal and the delayed fast-edge compressed signal to generate an output signal including a series of pulses having a width determined by the delay of the delayed signal. In one embodiment, the delay device is a shorted transmission line stub having a length selectively set by a series of MEM devices. In another embodiment, the delay device is an NLTL variable time delay device that delays the fast-edge signal.