Focused Planar Electromagnetic Waves for Enhanced Near-Field Microwave Imaging With Verification Using Tapered Gradient-Index Lens Antenna

Radar-based algorithms for electromagnetic (EM) imaging are developed based on the assumption that EM has a local planar wave front inside the imaging domain. However, this might not be the case for majority of utilized antennas as the imaged object is usually located within the near-field zone of the antenna. The impact of that assumption on imaging accuracy and whether utilizing an antenna that can create a focused planar wave front inside the imaging domain improves EM imaging are investigated in torso imaging as an example. Thus, three types of antennas are used to scan the torso; 1) bio-matched loop-dipole, 2) Gradient-Index lens (GRIN), and 3) Tapered GRIN (T-GRIN) lens antenna. The proposed T-GRIN lens antennas is designed to create a focused plane wave propagation inside the torso using tapered trapezoid water-filled cavities inside a host medium. The proposed design improves penetration depth by 33% compared to conventional GRIN lens and 75% compared to the bio-matched loop-dipole antenna, in a wide fractional bandwidth of 83% at 0.7-1.7 GHz. The realized results indicate that generating focused plane wave inside the imaged object, which is realized using T-GRIN lens antenna, improves the detection accuracy by 15 % and 56% compared to conventional GRIN lens and bio-matched loop-dipole antennas, respectively. Moreover, the localization accuracy is improved by 54.5% and 100% compared to conventional GRIN lens and bio-matched loop-dipole antenna, respectively. This study highlights the importance of creating focused planar wave front within the imaging domain for improved detection and localization using microwave techniques.

Automated summary

This study investigates the impact of assuming a local planar wave front on the accuracy of electromagnetic (EM) imaging and explores the use of a lens antenna to improve imaging. The results show that the proposed tapered GRIN lens antenna improves the detection accuracy and localization accuracy compared to conventional GRIN lens and bio-matched loop-dipole antennas. This highlights the importance of creating a focused plane wave front within the imaging domain for improved detection and localization using microwave techniques.