TE-polarized bessel-beam launchers for wireless power transfer at millimeter waves: theory, design, and experimental validation

Transverse-electric (TE) polarized Bessel-beam launchers working at millimeter-wave frequencies are theoretically described, simulated, realized, and experimentally validated. A limited-diffractive near-field distribution up to the so-called nondiffractive-range distance of about 30 mm has been obtained in this work. To generate a pure TE leaky mode, avoiding undesired transverse-magnetic (TM) field components, an innovative feeding scheme is designed consisting of a circular array of four radial slots. To enhance compactness, the four slots are excited through a single-port meandered microstrip feeding network, which has been optimized to ensure the same signal distribution exciting the slots while minimizing unwanted coupling among them. Full-wave simulations allowed for accurately designing a resonant cavity at 30 GHz able to generate a TE-polarized Bessel beam (BB). Two launchers of this kind are then exploited to create a wireless power transfer (WPT) link whose performance is first computed numerically and then verified by means of measurements for different transmitter-receiver distances, namely 25, 35, and 48 mm. These values respectively fall within, in proximity of, and away from the nondiffractive region of the transmitting (TX) device, showing an increasing WPT performance deterioration, as expected. For the case of a 25-mm distance, the evaluated |S-21| is - 12 dB, in excellent agreement between full-wave and measurement results.