Low Complexity Beam Steering Antenna Array Using Beamforming Network Subarrays

Lens antenna subarrays were recently shown to provide reduced hardware complexity with relatively wide scan angles as compared to conventional subarray approaches. Despite being used in subarrays, lenses still become physically large below mm-wave frequencies making it difficult to enable compact antenna realizations. First time this paper investigates a lens antenna subarray technique for below mm-wave band applications by replacing the lenses of subarrays with beamforming networks. The presented linear antenna array design employs 16 patch antenna elements grouped into 4 subarrays. Each subarray employs a 4×4 Butler Matrix with a single pole four throw switch while subarrays are phased using digital phase shifters. The design benefits from the beam steering capability of the subarrays to operate at 10 GHz with a $\pm 60^{0}$ scan range. Scanning with 7 ⁰ ($\approx$ half power beam width) increments show a worst case side lobe level (SLL) of 6 dB for 2 beams that become adjacent to crossover beams of the Butler Matrix, while other beams exhibit better than $\approx 8\mathrm{d}\mathrm{B}$ SLL. A design layout is presented that shows multilayered printed circuit board manufacturing can be harnessed to fit electronics within a footprint that allows realization of a half wavelength spaced antenna array.