Broadband conical helix antennas

The extended need for circularly polarized antennas has increased with the growing demands of telemetering, countermeasures, and communications in the aircraft and guided missile field. The inadvertent cross polarization which occurs from linearly polarized sources as a result of reflection has also imposed such a need in the field of satellite tracking. The desirable antenna characteristics for these particular applications are: (a) Constant beamwidth in both planes (b) Low axial ratio (c) Low beamtilt (d) Optimum match to a standard 50 ohm line Coupled with these requirements is the all important one of maximum attainable bandwidth to reduce the number of structures required to cover the assigned frequency spectrum. Circularly polarized antennas, in the past, have been restricted to crossed dipoles fed in quadrature or cylindrical helixes mounted on ground planes. The maximum attainable bandwidth of these antennas, being extremely frequency sensitive, is 2:1 or less. The conical helix was suggested by Dr. Kraus of Ohio State University some time ago and more recently by J. S. Chatterjee of the University of Calcutta as reported in the Journal of Applied Physics.