The radiating part consists of 8 × 8 subarrays (16×16 slots in total), where they are fed by the same phase and amplitude. The subarrays are formed in two distinct layers, i.e., the cavities (placed at the top side of layer 3) and the radiating layer (on layer 4). The topside of layer 3 contains 8×8 cavities that feed the 16×16 slots of layer 4 uniformly.The geometry of the feed network and the radiating elements are shown, in more detail, in Fig. 2(a)–(c).