Reflectarray Design With Similarity-Shaped Fragmented Sub-Wavelength Elements

A new technique for synthesizing reflectarray antennas is presented. It utilizes fragmented elements in a manner that allows the elements of the reflectarray to be shaped-optimized so that a high degree of geometrical similarity is maintained between adjacent elements. The implication is that in a reflectarray of such elements each element will see an electromagnetic environment that more closely emulates the infinite periodic one used to compute the element properties. We show experimentally that this indeed results in aperture efficiencies closely approaching the upper bounds achievable for some selected feed system, and offers a significant improvement over that obtained with conventional reflectarrays (that is, those not using similarity-synthesized fragmented elements). It is also shown that a reflectarray surface that uses fragmented elements can be simultaneously patterned with a visual image while still closely maintaining the desired reflection phase from its surface to yield a high-gain antenna.