Researches on radiation performance improvement of microstrip reflectarray antennas

The performances of reflectarrays are mainly determined by the characteristics of the elements. In this communication, various microstrip reflectarray elements to improve reflectarray performances are reviewed. Based on the figures of merits of the element (reflection phase range, sensitivity, and bandwidth) multi-layer elements, concentric multi-ring / patch element, and subwavelength elements are reviewed. Also, reflectarrays with elements having bandgap characteristic to reduce mutual coupling between the elements are reviewed.