Radio Antenna Engineering is a free introductory textbook on radio antennas and their applications. See the editorial for more information....

Six-wire Side-connected Balanced Feeder

Author: Edmund A. Laport

This type of line (Fig. 4.25) is one that can be constructed on the same plan as the four-wire side-connected line, but with three wires per side. This decreases the characteristic impedance over that of the four-wire side-connected type for the same sectional dimensions and consequently raises its power-transmission capacity. The spacings between the three wires on one side can be equal or unequal, providing some degree of adjustment of the characteristic impedance for special applications while using the same materials.

Fig. 4.25

The middle wires carry less current than the corner wires so that the amount of copper used increases somewhat faster than its effectiveness. Nevertheless, the increase in current-transmission capacity and the decrease in the characteristic impedance and the over-all attenuation per unit length are desirable trends as more power has to be transmitted.

Figure 4.35B shows how a short section of this construction may be used as a series transforming section in certain impedance-matching operations. For this type of line, when h » a, b,


The computed characteristics of a sample line are the following (compare with fifth line of the table for the type XVI line):

ρ (inches) a (inches) b (inches) A Z0 (ohms)

ρ, inches

a, inches

b, inches


Z0, ohms






The current in either middle wire is 81.7 percent of that in one of the corner wires for this example. This is also a direct measure of the relative effectiveness in copper utilization. The copper loss for this line is 87.5 percent of that for the four-wire side-connected line of the same cross section, and the insulation loss is 85.5 percent.

Last Update: 2011-03-19