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.

Abstract: A radar receiver for indicating the presence of a source of microwave energy includes an antenna, a modulation oscillator and modulator diode, a detector diode connected to bandpass amplifier stages, a peak detector providing a signal proportional in level to the received microwave energy signal strength, and a voltage controlled oscillator (VCO) connected to the peak detector and having a frequency in proportion to the peak detector signal level, the frequency of the VCO being an indication of range from a source of radar and a change in frequency being an indication of a rate of approach thereto. The VCO controls a transistor switch, and alarm output devices are connected through the transistor with alarm power sources, whereby an alarm signal activates the output device at a frequency related to the microwave signal strength.