Negative-refractive-index transmission-line metamaterial-loaded dipole antennas

Several compact, fully-printed negative-refractive-index transmission-line (NRI-TL) metamaterial-loaded dipole antennas are proposed. The antennas achieve multi-band behaviour by loading a host dipole antenna with series capacitive gaps and shunt inductive strips. In an approach proposed by Schelkunoff, the two arms of the dipole antenna are modeled as the two conductors of a biconical transmission line, and thus the rich dispersion properties of the NRI-TL structure are exploited, while still creating an effective radiator. Both dual-band and tri-band versions of the antennas are shown, with individual bandwidths ranging from 40 MHz to 1.4 GHz. It is also demonstrated that the antennas can achieve a size miniaturization factor of approximately two, and that they exhibit uniform dipolar radiation patterns. Throughout their bands of operation the gain and radiation efficiency vary from approximately -3 dBi to 2.3 dBi and 42% to 98%, respectively.