Low-Sidelobe-Level Millimeter-Wave Asymmetric Bulls Eye Antenna With Minimal Profile Feeding

Bull's eye antennas exhibit remarkable directivity considering their low profile, albeit accompanied by high sidelobes. This undesirable radiation characteristic is tackled here by reporting a complementary split ring feeding whereby the broadside space-wave partially responsible for the high sidelobes is cancelled while the leaky wave is excited effectively. This feeding results in an asymmetric bull's eye antenna with minimal profile (similar to 0.73 lambda(0)) and no protrusions on the radiating interface. The fabricated 10-period antenna operating in the Ka-band shows a directivity of 23.5 dBi, a sidelobe level of -22.9 dB (>6 dB improvement compared to other bull's eye antennas) and a beamwidth of 3.7 degrees and 6.7 degrees in the E- and H-plane, respectively.