Constructing normal-mode helical antennas

Helical antennas have made a marked impression on the communications industry due to the growing demands of telemetering, command and control and communications in the aircraft and guided-missile field. Helical antennas in the above fields are always circularly polarized and act in the axial mode. Compared to the axial-mode helical antennas, little attention has been paid to normal-mode helical antennas because of small bandwidth and low efficiency. However, it has been found recently1 that normal-mode helical antennas have certain considerations which far outweigh their disadvantages. These considerations are height reduction, ease of installation, and cost. It has been suggested1 by the author and his co-workers that it is quite possible to use normal-mode helical antennas in the medium and short wave region, thereby reducing the height of the mast antenna by a factor of 5 to 10. This paper discusses in detail the design and construction of vertically polarized normal-mode helical antenna structures.