Design of Overlapped Subarrays Based on Aperture Reactive Loading

A novel technique is presented for the design and optimization of waveguide antenna arrays based on overlapping subarrays for limited field-of-view (FoV) applications. Each subarray consists of one directly fed antenna element and several passive reactive-loaded elements. The proposed overlapping scheme exploits a free-space reactive coupling instead of more conventional schemes based on complex beamforming networks. This results in a drastic reduction in the number of waveguide components required in the feeding network. The optimization of the considered class of array structures using a full-wave electromagnetic (EM) solver is extremely time-consuming even in the presence of subarrays with a reduced number of passive elements. To overcome this limitation, an effective semi-analytical design algorithm has been specifically developed. Using this algorithm, a novel subarray structure with a predefined pulse-shaped radiation pattern was synthesized. The designed subarray is inherently matched and features reduced spurious EM coupling level with adjacent subarray elements. In particular, the analysis of an array consisting of 38 such subarray elements has been carried out with the main goal of illustrating the effect of the subarray pattern on the total array characteristics. To validate the subarray overlapping scheme, an array composed of three contiguous subarrays has been realized and measured experimentally. In this way, a scan range in the FoV [-4°; 4°] with 15 dB grating lobe suppression has been demonstrated.