Enhancing Long-Range Battery-Free Communication: A Passive Lens-Enabled Broadbeam Harmonic mmID for Emerging IoT Systems

For the first time, the authors propose a novel 3D lens-enabled, fully-passive harmonic retrodirective mmID with wide spherical angular coverage and ultra-long-range capabilities. The mmID features a bi-convex dielectric lens for high gain and solid angular coverage, paired with an RF front-end comprised of 25 capacitive-coupled dual-polarized 'pixel' antennas and a fully-passive frequency-doubling circuit. The proposed system achieves a solid angle coverage of 2.68 sr and a peak RCS of -31.9 dBsm, representing the highest detectability across solid angles among harmonic RFIDs. The mmID was tested up to 150 m at incident angles of 0° and 55°, to demonstrate its ultra-long range capabilities even at highly oblique angles. With <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 \mathrm{G} / \text{mm}$</tex>-Wave EIRP of 75 dBm, the mmID is projected to reach ranges of 2.7 km at boresight and 1.6 km at 55°. With its fully-passive design and high detectability, this mmID offers a transformative solution for next-generation ultra-long-range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{5 G} / \mathbf{m m W a v e ~ I o T ~ a p p l i c a t i o n s. ~}$</tex>