Zeroth-order resonant circular patch antenna based on periodic structures

The circular patch antenna loaded with a periodic structure implementing a composite right/left-handed transmission line (TL) is introduced. The corresponding circuit model of the radial TL is derived to analyse this circular antenna. Since the unit cells of this TL can support arbitrary phase shift, the antenna can form negative modes, positive modes and zeroth-order resonant (ZOR) modes. For a ZOR antenna, the resonant frequency is independent of its physical size. The resonant frequency, input impedance and radiation characteristics of the ZOR circular antenna are analysed in terms of the physical parameters of the unit cells. Two ZOR circular antennas are designed showing monopolar radiation patterns. One is electrically extremely large, yielding a high directivity, and the other one is electrically small.