This paper discusses the theoretical modeling and practical design of
millimeter wave reffectarrays using microstrip patch elements of varia
ble size, A full-wave treatment of plane wave reflection from a unifor
m infinite array of microstrip patches is described and used to genera
te the required patch-design data and to calculate radiation patterns
of the reflectarray, The critical parameters of millimeter wave reflec
tarray design, such as aperture efficiency, phase errors, losses, and
bandwidth are also discussed, Several reflectarray feeding techniques
are described, and measurements from four reflectarray design examples
at 28 and 77 GHz are presented.