5Beam Reconfigurable Reflectarrays and Transmitarrays
5.1 Introduction
Reflectarrays and transmitarrays have received a significant amount of research interest recently. Reflectarrays combine the advantages of reflector antennas and phased arrays. A conventional microstrip reflectarray consists of a printed array (e.g. of patch antennas) illuminated by at least one feed antenna such as a circular horn. Each radiating element is designed to provide a pre‐adjusted phase to form a focused beam to the desired direction. At its operation frequencies, a reflectarray antenna can substitute the traditional parabolic reflector with a lightweight planar structure. A transmitarray antenna also consists of feed antenna(s) and an array of unit cells. Different from the reflectarrays, the array of unit cells transmits the waves instead of reflecting them back. Thus, a transmitarray is referred to as a ‘planar lens’ in some literature. The transmitarrays place the feed antenna directly in front of the aperture without incurring any blockage losses. This is especially advantageous when there is a need to use multiple feeds to obtain multi‐beams or beam‐switching.
For a low‐cost smart antenna design, reflectarrays and transmitarrays are quite attractive for two reasons. First, they employ spatial feeding instead of using traditional feed networks. This is an important advantage as it enables a significant reduction in system complexity and cost, particularly when there is a need to use a large number ...