Generation of an Electromagnetic Jet Using a PTFE-Loaded WR90 Waveguide: Design and Characterization

We present a compact dielectric lens integrated at the aperture of a WR90 rectangular waveguide, achieved using polytetrafluoroethylene (PTFE). This innovative configuration enables, for the first time in the X- and Ku-bands, the direct generation of a subwavelength electromagnetic jet from a guided structure. The beam exhibits the hallmark features of an electromagnetic jet: strong near-field focusing, a subwavelength beam width surpassing the diffraction limit, and a quasi-planar wavefront sustained over a propagation distance of about 2λ. The lens design was systematically optimized, and its performance was assessed through full-wave finite element simulations and experimentally validated on a fabricated prototype. Excellent agreement between the simulation and measurement confirms the robustness of the approach. Beyond its simplicity and low cost, this solution achieves state-of-the-art focusing performance compared to free-space and guided-wave alternatives. It offers strong potential for applications in high-resolution imaging, precision sensing, and material characterization, particularly in opaque or highly lossy environments.