An electronically tuned HF/VHF helical antenna
Abstract
The principles of a tunable helix design are presented as well as a mathematical model of the helix, and it is pointed out that the tuning range of the helix is a prime design parameter. The antenna, a normalmode helix, produces a radiation pattern that is predominantly vertically polarized and is similar to that produced by a standard monopole. As the antenna is tuned higher in frequency, the radiation resistance increases rapidly and becomes larger than the antenna loss resistance at higher frequencies. Design tradeoffs, voltage and current distributions, helix tuning circuits, and diode selection and limitations are covered. It is shown that closely spaced tunable helical antennas operating at different frequencies do not affect tuning. Examples of 6ft and 9ft HF helixes designs generated from the presented equations and curves are given.
 Publication:

Microwave Journal
 Pub Date:
 May 1991
 Bibcode:
 1991MiJo...34..223P
 Keywords:

 Antenna Design;
 Helical Antennas;
 High Frequencies;
 Tuning;
 Very High Frequencies;
 Antenna Radiation Patterns;
 Bandwidth;
 Mathematical Models;
 Monopole Antennas;
 Communications and Radar