A planar slot array with four independent beams

Active Doppler velocity sensors require an antenna system that generates three or more independent beams. A four-port dual-mode antenna that generates four independent beams from a single aperture is described. The signals emanating from the four ports generate four beams in space through a common aperture of crossed slot radiators. Isolation between the four signals processed through the antenna is obtained primarily by utilizing the mode isolation that exists between the and modes in square waveguide. The isolation obtained between ports was 27.5 dB or greater. The special design problems and the effect of dimensional tolerances on the port isolation are discussed. A gain of greater than 30 dB for each beam and an overall antenna efficiency of approximately 71 percent were achieved. The beam pointing directions ranged from 27 to 29 degrees from the normal to the aperture. Sidelobes of 15 dB or better were also obtained.