Radiation Resistances of Loaded Antennas

Short cylindrical antennas have been loaded to resonate at frequencies lower than their natural frequencies by means of dielectric sheaths of cylindrical and conical form. These loadings are compared experimentally with loading by means of metal disks at the ends of the antennas. Resistances at resonance calculated by the Poynting vector method for two assumed current distributions are compared with the experimental results. It is shown that for a given current distribution at resonance, the antenna radiation resistance depends only on the antenna length in wave-lengths. Particular loading methods alter the current distributions. Those which produce more nearly uniform current distributions yield higher radiation resistances.