Wideband Wide-scanning Phased Array of U-slot Microstrip Antenna Elements in Triangular Lattice

Abstract

A compact, wideband and wide-scanning planar microstrip antenna array is investigated over X band. The element is a low-profile U-slot microstrip antenna fed by $50\Omega$ coaxial feed. The array is arranged in triangular lattice for element number reduction. The infinite array is able to achieve 28.9% bandwidth in E-plane, 28.4% bandwidth in D-plane and 22.5% bandwidth in H-plane when scanning to $\pm 60^{\circ}$ with VSWR $\leq 2.5$ . An array of seven elements with triangular lattice arrangement is fabricated and measured, showing satisfying agreement with simulation results. The individual VSWR bandwidth of each element reaches over 3GHz when VSWR $\leq 2.5$ . The center element achieves over 2.85GHz bandwidth for active VSWR $\leq 2.5$ and a side element achieves over 3.5GHz bandwidth for active VSWR $\leq 2.1$ when scanning to $\pm 45^{\circ}$ in all azimuth planes. The measured scanning pattern of the center element illustrates $115^{\circ}$ and $105^{\mathrm{o}}$ 3dB beamwidth in E-plane and in H-plane respectively, with cross polarization level below $-30\mathbf{dB}$ . The element is capable of radiation with over 5.5dB peak gain during the X band. The scanning performance of a $8\times 8$ array is synthesized, showing the ability of scanning up to $60^{\circ}$ of a H-plane connected planar array.