A circularly polarized slot array antenna in millimetre band is presented. A cosecant amplitude coverage in the elevation plane, as well as a 6° tilted monopulse pattern in the azimuth plane, is obtained. The radiating slot array is implemented over substrate integrated waveguides (SIW). A microstrip feeding network with coaxial to SIW transitions is designed for the elevation radiation pattern. The monopulse feed is implemented in metallic rectangular waveguide, which is connected to the elevation feeding network by means of microstrip to waveguide transitions. A gain peak value of 28.6 dBi and 79% of efficiency at 36.7 GHz has been obtained in the specified operation band (36.7-37 GHz) for a manufactured antenna prototype. Likewise, the top measured axial ratio is 1.95 dB at 36.85 GHz.
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