“…In recent years, many metamaterials, which exhibit unique properties, have been widely used for microwave component and antenna applications. [5][6][7][8][9] Among them, low/zero-index (LIM/ZIM) materials have features of controlling the direction of emission. 7,8 In Zhou et al, 9 with ZIM structure as the superstrate of a microstrip patch antenna, 1 dB-2 dB gain improvement is obtained.…”