Archimedean spiral antenna over a PEC reflector with a thin magnetic sheet

An Archimedean spiral antenna over a perfect electric conductor (PEC) reflector with a thin magnetic sheet is analyzed under the condition that the space between a spiral antenna and a PEC reflector is extremely narrow (0.007 wavelengths at the lower operating design frequency of 300 MHz). The permittivity of the magnetic sheet is about 15 times larger than permeability with the relatively large magnetic loss tangent. The analysis is performed using the finite-difference time-domain (FDTD) method. First, we analyzed the axial ratio characteristics when the distance between the spiral antenna and the PEC reflector with the thin magnetic sheet are changed. It is revealed that good axial ratio characteristics are obtained as the distance become narrower. Next, we describe the radiation characteristics of the spiral antenna when the distance of the antenna and the PEC is 0.02 and 0.007 wavelengths. Good axial ratio and input impedance characteristics are obtained in the case of 0.007 wavelength. We can conclude that this antenna can be applied for airborne based wideband antennas.