High-Sensitivity Microwave Detection of Subwavelength Objects Using a Dielectric-Loaded Waveguide With Electromagnetic Jet Lens

This letter presents a high-sensitivity, noncontact sensing approach based on a 15 GHz electromagnetic jet for the detection of subwavelength-scale objects. The jet is generated by a rectangular waveguide partially filled with polytetrafluoroethylene (PTFE) and terminated by a rectangular dielectric lens extending into free space. An impedance-matching transition between the empty and PTFE-filled sections of the waveguide is optimized to minimize insertion loss resulting in a single, easily insertable dielectric component that ensures seamless integration into the waveguide. The lens geometry is designed through full-wave simulations to achieve subwavelength focusing. The proposed structure produces a focal spot with full width at half maximum of $0.41\lambda$ and $0.59\lambda$ in the $x$- and $y$-directions, respectively. Experimental results confirm the enhanced near-field confinement and demonstrate the detection of objects as small as $\lambda /400$, highlighting advantages over conventional open-ended waveguide configurations. Owing to its fully guided architecture, compactness, and ease of use, the proposed device is particularly well suited for high-resolution, noninvasive sensing and offers strong potential for transfer to industrial applications.