OPTIMAL DESIGN OF DIPOLE ANTENNAS BACKED BY A FINITE HIGH-IMPEDANCE SCREEN

Abstract

The performance of a short dipole antenna closely located above a flnite High-Impedance Surface (HIS) is addressed. The antenna behavior is thoroughly analyzed in the frequency range up to the HIS resonance within the region where the propagation of the TE surface waves is not allowed. In the flrst part of the paper the analysis of a dipole antenna above a grounded dielectric slab is considered, and then it is extended to the case of a substrate with a frequency selective surface printed on it. For all conflgurations, the radiation pattern of the structure and Front-to-Back Ratio (FBR) are reported and compared. It is shown that the presence of a suitable frequency selective surface, regardless of the shape of the periodic elements, guarantees the antenna matching but does not in∞uence the behavior of the radiation patterns and the front-to-back ratio in the frequency range where only TM modes are allowed to propagate. The front-to-back ratio has been found to be maximum when the size of the generic HIS is around 0.8‚g (where ‚g is the TM guided surface wave wavelength). All the speculations are supported by simulated and measured results.