Abstract: A signal at a frequency f.sub.0 is coupled through matching circuitry to the input of a parametric frequency multiplier stage. Non-linearities in this stage generate harmonics of the frequency f.sub.0, including a desired harmonic k.times.f.sub.0, where k=2, 4, 6, 8... . Unique output coupling circuitry presents a high load impedance to the parametric multiplier at the frequency f.sub.0, thereby enhancing harmonic generation, and transforms the impedance to signals of frequency k.times.f.sub.0 at the multiplier stage output to a desired value. The output coupling circuit includes two series connected transmission lines which couple between the output of the parametric multiplier stage and the multiplier output. A third transmission line, having an electrical length of one quarter wavelength at frequency f.sub.0, is connected as an open circuit shunt stub to the multiplier output, thereby effectively producing a short circuit thereat at f.sub.0.