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 dielectri c half-space of relative permittivity epsilon(r) is formulated using a finite-difference technique. This equation involves only single-integ ral calculations and is used to obtain the current distribution of a s quare spiral antenna. The validity of the current obtained is checked by FD-TD analysis, Based on the current distribution obtained, the rad iation characteristics of the spiral are evaluated. It is found that t he gain in the dielectric material is larger than that in free space, with a ratio of epsilon(r)(1.5) in the broadside directions. As epsilo n(r) increases, the circularly polarised radiation region bounded by t he critical angles in the dielectric becomes narrower and the resistan ce value of the input impedance becomes lower.