Multiple frequency microwave antenna

A method of detecting the presence of microwave signals at either of two selected non-harmonically related frequencies comprising the steps of:

• (a) reflecting said microwave signals from a first reflector to a second reflector spaced therefrom a distance which is a compromise between respective multiples of half wavelengths of said frequencies that are nearly similar in length which results in a voltage standing wave ratio between said reflectors which is acceptable at both of said frequencies;
• (b) focusing said microwave signals from said second reflector into a waveguide capable of propagating signals of either of said frequencies in the fundamental mode therethrough;
• (c) coupling said microwave signals into a coaxial sidearm including a center probe projecting into said waveguide, said sidearm having a single detector diode positioned therein for sharp tuning of said sidearm with said diode therein to one of said frequencies to thereby couple signals of said one of said frequencies to said diode and for broad tuning to the other of said frequencies;
• (d) sharply tuning a portion of said waveguide adjacent said probe to said other frequency to thereby couple signals of said other frequency to said detector diode;
• (e) converting said microwave signals to electrical signals by means of said coupling said microwave signals to said detector diode;
• and
• (f) indicating the presence of said electrical signals.

A microwave antenna tuned to both 10.525 gigahertz and 24.125 gigahertz comprising:

• (a) an elongated waveguide having rectangular cross-sectional dimensions of 0.622 inch by 0.311 inch, said waveguide having an aperture at a front end thereof and a backshort at a rear end thereof;
• (b) a first reflector and a second reflector mounted on said waveguide adjacent said aperture, said reflectors having respective reflecting surfaces cooperating to focus microwave energy through said aperture into said waveguide, said reflectors providing a substantially constant ray distance between the reflecting surfaces over major portions of said surfaces, said ray distance being 1.17 inches;
• (c) a single elongated coaxial detector diode sidearm operatively joined to said waveguide and having a single coaxial detector diode therein operative to provide an electrical signal in response to a microwave signal coupled into said sidewarm, said detector diode being positioned in said sidearm to sharply tune 10.525 gigahertz and to broadly tune 24.125 gigahertz;
• (d) said coaxial sidearm including a central conductive probe connected to said detector diode and projecting through said waveguide at a position spaced from said backshort a distance of 0.30 inch to sharply tune the portion of said waveguide adjacent said probe to 24.125 gigahertz;
• and
• (e) a single modulator diode positioned in said waveguide at a distance of 1.55 inches from said probe, said modulator diode being operative to chop signals of 10.525 gigahertz and 24.125 gigahertz passing through said waveguide.