Feeding Coils Design for TE-Polarized Bessel Antenna to Generate Rotationally Symmetric Magnetic Field Distribution

Abstract

Three feeding structures are proposed to feed a TE-polarized Bessel antenna for a rotationally symmetric magnetic field distribution. We first propose a spiral coil and a dual half-loop coil to achieve rotationally symmetric magnetic field, resulting in homogeneous current distribution on the coils. Unfortunately, the magnetic field distribution is very sensitive to the coil size for both structures. An alternative solution using a half-loop coil with mushroom structure is then designed to achieve robustness. Both the simulation and the measurement demonstrate that the proposed feeding structures can generate a rotationally symmetric magnetic field distribution; the proposed spiral coil is simple and efficient, while the half-loop coil with mushroom structure is robust.