Design and evaluation of a three-beam LMDS central station antenna using reflectarrays

A two-layer reflectarray is proposed as a central station antenna for local multipoint distribution system (LMDS) in the band 24-26 GHz. The reflectarray is illuminated by three feeds, which are used to generate independent beams in azimuth, in order to cover adjacent 30deg sectors. The beams are shaped both in azimuth and in elevation. A phase-only pattern synthesis technique is applied to obtain he phase-shift distribution on the reflectarray surface required that produces the shaped pattern for the central beam. Then, the dimensions of the printed stacked patches are adjusted to produce the required phase-shift at each element. Although the reflectarray cells are placed in the Fresnel near-field region of the feed-horns, a far-field model of the horn is used for the design. Finally, the near field generated by the horn is used to compute the radiation patterns of the reflectarray, and the results are close to those obtained with the far-field model. The radiation patterns for both central and lateral beams exhibit a shaping close to the requirements