Exploiting Higher Order Modes for Grating Lobe Reduction in Scanning Phased Array Antennas

A new approach is proposed to reduce the grating lobes by exciting higher order modes of conical radiation patterns in microstrip phased array antennas with a one-wavelength element spacing for medium- and wide-scan angles. The proposed concept utilizes the scanning and nulling capabilities of combined higher order modes of a circular microstrip patch as an antenna element in a seven-element hexagonal array. These elements facilitate providing suitable radiation-matched patterns for wide-scanned angles and simultaneously reducing the grating lobes for large element spacing in the order of one wavelength. In particular, for the scan angles of 35°-75°, two higher order modes, namely the TM21 and TM31, are excited and the grating lobes are reduced to well below -30 dB. The proposed method is also shown to be effective for near the horizon scanning with a $0.8\lambda _{\mathrm {o}}$ element spacing.