Linearly and curvilinearly tapered cylindrical- dielectric-rod antennas

The body-of-revolution finite-difference time-domain (BOR-FDTD) method is applied to the analysis of a tapered cylindrical-dielectric-rod fed by a metallic waveguide with a launching horn. Before evaluating the wave propagating along the tapered rod, we design the launching horn to efficiently excite the fundamental guided-mode of a uniform rod. After confirming the effectiveness of the launching horn, guided-mode conversion properties are evaluated in linearly and curvilinearly tapered rods. As a result, the guided mode excited at the feed end is smoothly converted into that at the free end in a curvilinearly tapered rod. It is numerically revealed that the smooth guided-mode conversion leads to the expansion of the equiphase field region in a terminal aperture with a subsequent increase in the gain. The calculated radiation patterns are in good agreement with experimental data.