Low Sidelobe Level, High-Gain Patch Antennas Operating at Higher-Order Modes

High-gain patch antennas with low sidelobes are proposed in this article. First, the patch antennas are operating at higher-order modes to realize a larger electrical size and higher directivity. TM30 mode is selected for a rectangular patch, while TM21 mode is selected for a circular patch. Through the surface current distribution analysis, the sidelobe is found contributed by the opposite-oriented surface current. To reduce the sidelobe, one slit and two slots are introduced to the patch on the area with opposite-oriented current. Furthermore, two parasitic patches are introduced to the etched area of the patch. Current with the same orientation is excited through coupling, which helps to further enhance gain and reduce the sidelobe. For demonstration, the rectangular and circular patches are designed and fabricated. In the measurement, 11-12 dBi gain with sidelobe as low as -28 dBi at both E- and H-planes are found. The front-to-back ratio of both patches are found better than 30 dB in the measurements.