Abstract: The present invention relates to a reflectarray antenna. The reflectarray antenna comprises a dielectric substrate layer disposed on a ground plane. An array of radiating elements such as microstrip patches of similar size are arranged into a regular lattice configuration on the top surface of the substrate layer. A periodic configuration of slots of variable size are provided at the bottom surface of the substrate layer. A required phase shift at each position on the reflectarray surface is obtained by adjusting the slot length on the ground plane. The incident wave from the feed excites the dominant mode on the microstrip patches The presence of slots acts as an inductive loading of the patches, which introduces a phase shift in the patch response. The inductance of each slot depends on its length.