Understanding the behavior of miniaturized metamaterial-based dipole antennas in leaky wave regime

We investigate the frequency behavior of a half-wave dipole antenna placed very close over a 2LC uni-planar compact electromagnetic bandgap (UC-EBG) structure. A very compact and high-gain antenna is realized at 1 GHz. The air distance between the dipole element and the UC-EBG surface is similar to lambda (0)/100. We analyse the structure by using the optical model of Hansen, full-wave electromagnetic simulations (EM) and experimental characterizations. The analytical model of Hansen describes accurately the UC-EBG phase contribution to the total radiated field below 1 GHz. Above this frequency, the Hansen analytical model is in discrepancy with the measurements and full-wave simulations, which show split in the radiation patterns. We show that this phenomenon is induced by the power leakage of the fast-wave UC-EBG surface excited by the dipole source inside its leaky wave region. We propose an original model based on the Hansen optical analysis that takes into account the overall phenomena. The model includes the contribution of the weighted fields radiated by the cells of the UC-EBG. This model leads to very good agreements with measurements and full-wave simulations.