Cap-loaded folded antenna

The purpose of this paper is to present design curves and formulas that can be used to design the cap-loaded folded monopole antenna. As a result of a theoretical study and measurements made on the top-loaded folded antenna, it appears possible to build efficient antennas as low as .03 wavelength high with resonant resistance of 50 ohms and a half-power bandwidth of 8%. The electrical characteristics of the antenna are a function of height, size of the top hat, the diameters of the driven and folded conductors, and the spacing between them. Data will be presented to show the effect on the resonant height, resonant resistance, and bandwidth when these parameters are varied. The most important features of this antenna are its small height, high resonant resistance, and relative broad bandwidth; specifically, the bandwidth varies from 8% to 30% with heights from .03 wavelength to .09 wavelength. The resonant resistance may be chosen at will by varying the ratio of diameters of the folded to driven conductors. Practical values are 1 to 50 ohms for an antenna height of .03 wavelength and 20 to 300 ohms for .09 wavelength.