Numerical modeling of scan behavior of finite planar arrays of wideband U-slot and rectangular microstrip patch elements

Excitation of surface waves in finite microstrip antenna arrays causes occurrence of blind spots at certain scan angles, resulting in reduction of scan bandwidth. The primary aim of this investigation is a comparative modeling of scan element gain patterns in planar array architectures with coaxially-fed wideband rectangular U-slot and rectangular patch elements. An U-slot and a rectangular patch with an offset probe, each having the same radiating patch area, were designed, and simulated via the commercially software IE3D, to have 10 dB return loss bandwidths of 26% and 9%, respectively, on a substrate with ε_r = 2.55 and thickness d = 0.762 cms. Numerical results for the VSWR vs. frequency sweep and scan (active) element gain patterns vs. elevation angle θ in the principal pattern planes (Φ = 0° and 90°) at selected element locations in a 5 × 5 rectangular grid planar array, are included. These results show that the isolated, wideband U-slot element, in an array environment has a surface wave excited blind spot in the (Φ = 0°) or E-plane, which is demonstrably more prominent than the rectangular patch array.