Millimeter Wave Circularly Polarized Fresnel Reflector for On-Board Radar on Rescue Helicopters

The increasing use of millimeter waves for civil radar application, e.g., for automotive or helicopter obstacle detection- requires the development of high gain and low cost antennas in compact form. With this aim, a Fresnel reflector with circular polarization over 5 GHz bandwidth (76-81 GHz) has been designed, fabricated and measured. The gain remains higher than 32 dBi with a peak value of 35 dBi at 79 GHz. For obtaining this performance, specific patches have been designed. They are based on circular rings, rectangular and offset patches. Each of them converts an incident linear electric field into a circular polarized one.