Grating Lobe Reduction in Scanning Phased Array Antennas With Large Element Spacing

Large element spacing in phased array antennas generally causes grating lobes, which start to exacerbate for wide scan angles. Herein, a new approach is proposed to reduce the grating lobes of planar phased array antennas with considerably large element spacing in the order of one wavelength for both broadside and scanned radiation patterns up to 45 degrees. The array has a seven-element hexagonal configuration, consisting of dual-mode circular microstrip antennas. It is shown that for small scan angles up to 8 degrees, a tapered amplitude distribution reduces the grating lobes to below -30 dB, when only the dominant mode is excited in the antenna element. As for wider scan angles up to 45 degrees, an additional higher order mode needs to be excited as well to reduce the grating lobes down to -30 dB for the large element spacing of one wavelength. The proposed method also proves to be effective for wider scan angles up to 60 degrees for element spacing of three quarters of a wavelength. This approach leads to the realization of thinned arrays with less number of elements, in which the weighting functions and mode excitation of the elements can be controlled by an adaptive signal processing unit in scanning phased array antennas.