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 HE₁₁ 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.