A UWB Low-Profile Hemispherical Array for Wide Angle Scanning

We report the first low-profile array on a doubly curved surface that supports wide angle electronic scanning and ultrawide bandwidth (7:1 ratio). The array elements are based on the balanced antipodal Vivaldi antenna (BAVA). The antennas are optimized for a good impedance match in an infinite planar array environment and are then deformed to fit along the surface of a hemisphere. The array is comprised of 104 linearly polarized BAVA elements arranged along a quadrilateral mesh on the surface of a 100 mm diameter hemisphere. The antennas and SMP connectors are 3-D printed out of titanium. The array has grating lobe-free operation at frequencies < 8 GHz. The array can also maintain relatively low sidelobe levels above 8 GHz compared with planar arrays because the aperiodicity of the hemispherical element locations reduces the magnitude of grating lobes. The simulated and measured realized gain is within 1 dB of the theoretical limit from 2.5–18 GHz and scan angles with
$\theta \le {\mathrm {90}}^{\circ }$
except near 14 GHz where a resonance reduces the gain by 3 dB for some scan angles.