Near-Field Focus Radiation of Multibeam Phased Array of Antennas Realized by Using Modified Rotman Lens Beamformer

This paper presents the design of 2-D phased array of antennas to radiate collinear multiple beams properly distributed for near-field (NF) focus (NFF) applications. In the design, the 2-D array is first decomposed into single-column subarrays, where each of the subarrays is identically excited to radiate a vertically NFF beam with the focal points located at a designated distance along the boresight direction of each subarray aperture. Afterward, the NFF column subarrays become the elements of a 1-D horizontal collinearly located array to radiate horizontally NFF multiple beams. The horizontal NFF beamforming network is implemented by extending the basic concept of conventional Rotman lens beamformer for directional NFF multibeam applications. Thus, three feeding points are selected to determine the lens's profile such that the produced phases via the modified Rotman lens can be used to feed a planar array to radiate three NFF beams when the lens is excited at the three selected points, respectively. This antenna set is realized at 2.45 GHz for radio frequency identification applications to demonstrate the implementation concept. Both the simulation and experimental measurement results are shown to validate the feasibility.