Helical top-loading of electrically small monopole antennas

Comprehensive tests and analysis have been made of a novel form of top loading for monopole antennas of about 0.03 wavelength electric height. The configuration has some advantages over the usual types of electrically small antennas, especially for high-power applications in the VLF to HF ranges. Since the helical top load resonates the entire structure, the supporting tower (and guy wires, if used) may be grounded, eliminating many high-voltage problems. Low-impedance coaxial transmission lines may be conveniently matched by tapping the helix, or in a number of other ways. Results are given for 20- and 200-foot models operating at 1500 and 150 kc, respectively. Parameters of bandwidth, efficiency and power handling capability have been extrapolated to other sizes and frequencies, including a 2000-foot design for VLF.