Monofilar conical-helix antenna with low pitch angle

The radiation characteristics of a monofilar conical-helix antenna are investigated on the basis of the theoretical current distribution. It is shown that the current distribution may be divided into two regions, and that a decaying current from the feed point to a point of the first minimum is the major contributor to the radiation. It is also found that the wideband usage requires the arm length to include the region up to the second minimum at the lowest operating frequency. Experimental data concerning the input impedance and radiation characteristics are presented to verify the numerical results.