Dual-Sense Circularly Polarized Substrate Integrated Waveguide Antenna for Deep Torso Imaging

A compact dual-sense circularly polarized (CP) antenna is presented for torso imaging, offering deep electromagnetic (EM) wave penetration and improved imaging capabilities. The design starts with a single-sense antenna on a circular base, using a square patch and substrate-integrated waveguide (SIW) to enhance EM wave penetration into the torso. Sleeved feeding and slow wave techniques are adopted to broaden the CP bandwidth without increasing the size. The final dual-sense CP antenna, with both left-hand and right-hand CP and dual feeds, has a 3.9 dB signal-to-mean-clutter ratio more than the single-sense design. It operates from 0.64 to 2.22 GHz (107% Fractional Bandwidth) with a compact size of 75 mm diameter and 8 mm thickness. Despite avoiding using a bulky lens, the antenna outperforms recent similar antennas by up to 248% in penetration in the torso while using a more compact structure. The proposed antenna generates in-depth E-fields across vertical and horizontal directions, enhancing imaging quality by collecting more accurate data. The antenna is tested on a torso phantom in three imaging scenarios using an optimization-based confocal imaging algorithm. It achieves a 129% improvement in detection accuracy compared to a single-sense CP antenna.