Compact Dual-Polarized Cavity-Backed Antenna With Wideband Performance for Deep Torso Imaging

A compact ultra-wideband cavity-backed dual-polarized antenna for torso imaging is presented. The antenna is specifically developed to achieve deep penetration and enhance detection accuracy. The design process involves placing two bowtie radiating elements orthogonally to generate vertical and horizontal polarization. Half-wavelength curved slots etched at the radiating elements create additional resonant frequencies and expand the operating bandwidth. A square cavity is used to back the antenna, ensuring unidirectional wave propagation and impedance matching for low-order modes. Via-fencing of the radiator is employed to confine surface currents, resulting in improved isolation (better than 20 dB) and electromagnetic wave penetration (more than 20% improvement at different frequencies). The antenna covers the frequency range of 0.17–1.74 GHz (164% fractional bandwidth). Despite its compact size (
$0.05\times 0.05\times 0.03\,\,\lambda ^{3}$
, where
$\lambda $
represents the wavelength at the lowest operating frequency), the antenna demonstrates enhanced wave penetration into the human torso by 172% and 62% compared to recent gradient index lens antennas and tapered gradient-index lens antennas, respectively. Notably, this improvement is achieved with much lower complexity and reduction in weight. The imaging capability of the antenna is assessed using a realistic average-male torso phantom and an optimized-based confocal imaging algorithm. The results reveal a significant enhancement of at least 35% in the signal-to-mean-clutter ratio (SMCR) when a dual-polarized antenna is employed. The dual-polarized antenna enables detecting targets at any location, shape, and orientation within the torso.