Square spiral antenna on dielectric half-space: analysis using an electric field equation formulated by a finite-difference technique

A tangential electric field equation for a wire antenna on a dielectric half-space of relative permittivity ε_r is formulated using a finite-difference technique. This equation involves only single-integral calculations and is used to obtain the current distribution of a square spiral antenna. The validity of the current obtained is checked by FD-TD analysis. Based on the current distribution obtained, the radiation characteristics of the spiral are evaluated. It is found that the gain in the dielectric material is larger than that in free space, with a ratio of ε_r^1.5 in the broadside directions. As ε_r increases, the circularly polarised radiation region bounded by the critical angles in the dielectric becomes narrower and the resistance value of the input impedance becomes lower