Nonuniform FSS-Backed Reflectarray With Synthesized Phase and Amplitude Distribution

A nonuniform frequency selective surface (FSS)backed reflectarray with both amplitude and phase controls for beam shaping is presented in this paper. In the process of element design, a dual-resonance reflectarray element backed by a loop FSS is studied. The proposed reflectarray element can achieve a reflection phase range of 570° and an amplitude control range over 10 dB, by tuning the dimensions of the upper reflectarray and lower FSS layers. In the process of reflectarray synthesis, a complex amplitude synthesis technique, based on the modified alternating projection method, is developed to take into account the physically realizable amplitude and phase controls of the FSS-backed element for optimizing the amplitude and phase distributions on the reflectarray aperture. A nonuniform FSS-backed 16 × 16-element reflectarray with a sector beam in the azimuth plane and a pencil beam in the elevation plane is designed and fabricated. The simulation and measured results reveal that the proposed reflectarray antenna offers distinguishing features in terms of high-quality pattern with lower sidelobe level, lower cross polarization as well as lower radar cross section, compared to the reflectarray designed by the conventional phase-only synthesis technique.