A Self-Nulling Single-Layer Dual-Mode Microstrip Patch Antenna for Grating Lobe Reduction

A single-layer, dual-mode microstrip patch antenna with self-nulling patterns is proposed. The antenna consists of a circular microstrip patch antenna, surrounded by a shorted concentric ring patch, exciting the TM11 and TM21 modes, respectively. Adaptive radiation patterns with self-scanning and nulling capabilities are realized by concomitantly exciting these two modes. To attain the mode purity, four symmetrical arc slits, inspired by the surface current distribution of the TM21 mode, as well as two horizontal slits are placed in the ring patch. For the miniaturization purpose, the circular patch is loaded by three vertical slits. A prototype of the proposed antenna is fabricated and tested. The measured results are in good agreement with the simulation results. To showcase the effectiveness of the proposed self-nulling dual-mode antenna, it is employed as an antenna element in a linear scanning array with element spacing greater than one-wavelength to reduce its unwanted grating lobes.