Reconfigurable Transmitarray Design Approaches for Beamforming Applications

Recent advances in wireless sensing and communications have resulted in the need for antennas capable of high-directivity reconfigurable beamforming. Transmitarrays have been shown to be viable architectures, and two general design approaches have emerged: the layered-scatterer approach and the guided-wave approach. In this paper, we first investigate the beamforming capability of the layered-scatterer approach, generalizing the approach using impedance surfaces. Using Floquet mode analysis, we show that when a structure of this type is used to produce a pencil beam at angles greater than 20 degrees off-broadside, significant side-lobes are produced at large angles, regardless of the aperture size. Next, we present a fully reconfigurable 6 x 6 transmitarray based on a guided-wave approach that experimentally demonstrates both pencil beam scanning over a 100 x 100-degree window as well as shaped-beam synthesis, over a 10 percent fractional bandwidth. The conclusion from our investigations into these two approaches is that for general beamforming applications, the guided-wave approach is superior, achieving good bandwidth, scanning range, insertion loss, and small structure thickness, with only moderate fabrication complexity.