Backscattering from planar spiral antennas

Structural mode backscattering characteristics of planar spiral antennas with proper termination impedances are presented. The investigated spiral antennas contain a self-complementary two-arm Archimedean spiral, a self-complementary four-arm Archimedean spiral and our proposed four-arm bilayer spiral. Compared with the self-complementary two-arm spiral, it is observed that the self-complementary four-arm spiral has lower structural mode backscattering. Based on the observations of self-complementary two-arm and four-arm spiral antennas, a four-arm bilayer spiral is proposed and it is shown that this spiral can gain further reduction of co-polarized backscattering under the linear polarization incidence. Furthermore, the radiation characteristics of the spiral antennas are also presented. The good agreement between simulated and measured backscattering results of the fabricated spirals validates our design.