Broadband circularly polarized dielectric rod antenna excited by a cavity backed spiral.

This paper introduces a new broadband dielectric rod antenna with circular polarization that can be utilized in microwave imaging applications. The antenna utilizes a sine wave modulated Archimedean spiral to launch hybrid mode within the dielectric rod, resulting in a wide circular polarization bandwidth and high right-hand circularly polarized gain. The spiral's wideband nature and the rod's high-gain feature are used simultaneously. The antenna is excited using a linearly tapered microstrip balun that functions as a balanced transmission line. Throughout the operational bandwidth, the HE(11) mode is the single guided mode inside the rod. The measured results demonstrate that the proposed antenna achieves an ultrawide impedance and 3-dB axial ratio bandwidths of 56.9% from 3.9 to 7 GHz, along with a gain between 8 to 12.4 dBic.