Long-Wire Antennas

Author: J.B. Hoag

In transmission lines, the two conductors are kept close to each other in order that their fields will cancel and radiation will be kept to a minimum. With antennas, the conductors are separated from each other in order that as much radiation as possible can be secured. Figure 35 H shows the current distribution along an antenna in which the wires have been opened up to the fullest extent.

Fig. 35 H. Current distribution along a center-fed 7/2-wave antenna

A quarter-wave resonant feeder is used to connect the antenna to the transmission line. With proper connections, these antennas may be fed from the end or from any of the points one-quarter wave-length apart down the wire. Sometimes the conductors are not opened up fully 180° from each other. The V and the rhombic or diamond antennas of Fig. 35 I are of this type.

Fig. 35 I. " V " and Rhombic types of antenna

The V antenna directs the transmitted energy more or less sharply in both directions along the line bisecting the angle between the wires, while the rhombic antenna is uni-directional as indicated by the arrow. Further discussion of the directive properties of antennas will be given later.