Design of two-layer printed reflectarrays for bandwidth enhancement

A reflectarray consists of a planar array of microstrip patches on a grounded substrate with a certain tuning to produce a progressive phase shift when illuminated by a primary source. The progressive phase shift of the reflected field can be achieved by varying the resonant length of the patches. This technique allows a simpler manufacture and produces lower cross-polarization levels than the stubs of different length attached to the radiating patches. Reflectarrays are easier to manufacture than reflector antennas and present less distortion and cross-polarization at the cost of a narrower bandwidth. Since narrow bandwidth is the most restricting limitation of reflectarrays, in this paper we propose a double layer reflectarray, using patches of variable size, to increase the bandwidth and to reduce the sensitivity to manufacture tolerances.