I. Introduction
Planar reflectarrays represent a promising solution for the design of low-weight, low-cost and versatile antennas [1], [2]. Folded reflectarray antennas further improve the main features of the reflectarrays through a reduction of the overall weight and profile without affecting the antenna performance. The folded reflectarray principle, originally introduced in [3], is shown in Fig. 1. The field radiated by a central feed is reflected by a polarizing grid, on the top of the antenna. A second reflection is performed by the main reflector in which the printed elements add the required phase shift, compensating for the free space delay occurred along the paths between them and the feed. A polarization twist of 90° is to be performed on the lower reflector together with the phase adjustment so that the wave can pass the grid.