Application of Rotman Lens Beamformer for Relatively Flexible Multibeam Coverage From Electrically Large-Phased Arrays of Antennas

In this paper, we present the application of the Rotman lens beamformer (RLB) to excite a large-phased array of antennas for multibeam radiation with confined sidelobe levels (SLLs) and coverage area. For a compact architecture, the array is divided into subarrays of interleaved elements, where each subarray is excited by a stacked RLB with a much smaller physical size. The basic concept is to realize the theoretical phases required to produce a set of orthogonal beams by the discrete Fourier transform representation of excitation weightings. Thus, the focal points to feed the Rotman lens are selected on an elliptic arc to produce directional beams among this set of orthogonal beams. A periodic phase impression is afterward performed to excite the residue elements excluding the subarrays, which subsequently creates an amplitude taper of excitation to reduce SLLs. Theoretical concepts and numerical examples examining the effects of phase distortion arising from the RLB design in the beamforming are first investigated to validate the feasibility and applicable scope. Experimental measurement over an antenna prototype is presented to validate the design.