Design of a composite right/left-handed transmission line unit-cell for a U-shaped mushroom ZOR antenna based on left-handed metamaterials

In this paper, a metamaterial-based zeroth-order (ZOR) mushroom antenna is presented by using a new composite right/left-handed (CRLH) transmission line unit-cell implemented with a U-shaped top plate is presented to extend bandwidth. The ZOR antenna whose resonance frequency is independent of the antenna size can enable a reduction of the antenna size. Because the shunt capacitance is determined by the area of a mushroom patch, a U-shaped mushroom having a lower shunt capacitance than the Sievenpiper mushroom structure is properly designed to widen the small bandwidth of the CRLH TL antenna. Compared to a square-shaped mushroom structure, a U-shaped mushroom structure for three unit-cells provided a reduced shunt capacitance and increased the 10-dB bandwidth by 2.5 times at 9.37 GHz.