Specular Reflection Analysis for Off-Specular Reflectarray Antennas

It is known that for reflectarrays designed to radiate in an off-specular direction, part of the scattered field may still be directed in the specular direction. In this paper, a reflectarray made of single-layer patch elements is considered. The dependence of the unwanted specular reflection on the size of the patches is examined. Moreover, in a global analysis of the reflectarray, we show that this specular reflection can be due to a periodic error occurring in the applied phase shift. It is found that this periodic error is also responsible for the occurrence of a parasitic lobe in backward directions.