Realization of wideband characteristics for a spiral antenna backed by a conducting plane reflector

Abstract

It is shown that backing a spiral antenna with a conducting plane reflector narrows the inherent wideband radiation characteristics of the spiral by distorting the current distribution. When a small, circular conducting plane is inserted between the spiral and the plane reflector, the distorted current distribution can be changed to a traveling wave. This traveling-wave current has a decaying amplitude, leading to a desirable radiation beam of good circular polarization. The frequency band for CPW (circularly polarized wave) radiation can be extended from 1:1.18 without the small disk 1:1.42 with the disk.<>