Design of Multilayer, Dualband Metasurface Reflectarrays

Reflectarray antennas are typically designed under the local periodicity approximation. Thus, mutual coupling is modeled as though the array is infinite in extent and made of identical elements. In dualband reflectarrays, elements are typically designed separately, with those at one frequency band operating with elements at the other band in the background. Elements are typically tuned to find the best compromise between the reflectarray’s performance at one frequency versus the other. Such a design process leads to nonoptimal designs. Here, we present an algorithm to design both layers of the reflectarray at both frequencies simultaneously. The reflectarray consists of two metasurfaces above a ground plane. The method accurately accounts for mutual coupling within the homogenized reflectarray, without resorting to local periodicity approximations. The design process produces practically realizable structures fabricable with standard printed circuit technologies. Subwavelength element patterning of the reflectarray surfaces also give rise to higher bandwidth.