Abstract: A microwave antenna for use at a limited number of non-harmonically related frequencies, particularly two, includes a pair of reflectors, a detector diode, and a modulator diode mounted on a waveguide in operative spatial relationships which are compromises of closely occurring multiples of half or quarter wavelengths of the frequencies of interest. More particularly, the reflectors are spaced apart such a compromise distance which results in a low voltage standing wave ratio. The antenna includes a coaxial detector diode holder or sidearm positioned on the waveguide and in communication therewith at a position to provide sharp tuning at one of the frequencies while the detector diode is positioned in a coaxial diode holder at a location operative to sharply tune the other frequency. The modulator diode is positioned in the waveguide a distance from the detector diode holder which is a compromise distance based on in-guide half wavelengths at each of the frequencies.