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

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 50Ω 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 ±60
^°
with VSWR ≤ 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 ≤ 2.5. The center element achieves over 2.85GHz bandwidth for active VSWR ≤ 2.5 and a side element achieves over 3.5GHz bandwidth for active VSWR ≤ 2.1 when scanning to ±45
^°
in all azimuth planes. The measured scanning pattern of the center element illustrates 115
^°
and 105
^o
3dB beamwidth in E-plane and in H-plane respectively, with cross polarization level below -30dB. The element is capable of radiation with over 5.5dB peak gain during the X band. The scanning performance of a 8×8 array is synthesized, showing the ability of scanning up to 60
^°
of a H-plane connected planar array.