Study of a plane short on a shielded helix

Abstract

The results of probe measurements along a shielded helix terminated in a plane conducting "short" are given. These results seem to indicate that the higher-order fields at the short are reactive and that the minimums are shifted out from the normal 180-degree position. The amount of this shift seemed to be relatively constant at approximately 38 degrees from 500 to 2,000 megacycles for a particular helix. A very approximate analysis of the helix short is made where the helix and its image wire are considered as a tapered two-wire transmission line. The position of the first minimum is determined by a numerical integration using the transmission line equations. This analysis predicts the correct direction of the shift of the minimum and also gives a rough idea as to the amount of this shift over the given band of frequencies.