Grating Lobe Suppression of Sparse Phased Array by Null Scanning Antenna

Abstract

A grating lobe suppression approach based on the null scanning antenna (NSA) for a sparse phased array is proposed. The NSA provides continuous null scanning and beam steering on two orthogonal planes, by connecting four varactor loaded impedance reconfigurable circuits to the four edges of a square patch antenna, respectively. The NSA is introduced into a sparse phased array and the grating lobe is suppressed by keeping the radiation pattern null of NSA pointing at the angle of the grating lobe during beam scanning. Meanwhile, the beam direction of NSA is steered to a wider angle with the variation of null angle. The main lobes during beam scanning are located within the 3 dB beamwidth of NSA. Thus, the sidelobe level (SLL) and scan loss over the wide scanning region are improved considerably. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\,\,\times \,\,4$ </tex-math></inline-formula> sparse phased array with NSA is designed and measured for verification. Both simulated and measured results indicate that the SLL of the sparse phased array with NSA can be suppressed below −9.3 dB within the scan range from −76° to 75°. The maximum realized gain during beam scanning is 17 dBi, with an aperture efficiency of 69.86% and a maximum gain fluctuation of 4.4 dB.