Optimization of the exchange of energy between a free space wave and current flowing in the conductive helix of an axial mode, helical antenna is achieved by varying the pitch angle of successive turns of the antenna along the axis of the antenna, from a relatively small pitch angle at the base, feed location of the antenna, to a relatively large value at the distal end of the antenna. Pitch angles of successive turns of the antenna are varied in a non-linear manner to correspond to the non-linear manner in which the phase velocity of a wave propagating through the antenna varies relative to the phase velocity of a free space electromagnetic wave. For the case of an axial mode, helical antenna operating at C-band, the pitch angle of said antenna may be varied between 3-8 degrees at the antenna feed point to a 20-30 degrees at its free space-interfacing distal end. The variable pitch angle antenna has a gain versus bandwidth characteristic that contains a plurality of spaced apart peak regions, one of which has a peak gain slightly less than the other. This dual peak gain behavior permits application design trade off between a smaller sized antenna with slightly reduced performance versus a larger sized antenna with slightly higher performance.
展开▼
