Short-Lines

Author: J.B. Hoag

In the 1880's, Hertz carried out the first radio experiments, with damped waves only a few millimeters long. For many years thereafter, the trend was to use longer and longer waves, up to 20,000 meters or more. During the past twoscore years, the reverse trend has been followed, back again to the " microwaves," but with the important difference that undamped waves are used and that the tubes and circuits have been so thoroughly studied that accurately controllable and predictable operation can be obtained.

In this chapter we shall be concerned with the systems of conductors whose physical lengths are comparable to the wave-lengths of the radio waves. It is difficult to call these systems " circuits " or " lines " in the conventional sense, so the term " short-line " will be used. As in the case of long-lines discussed in the preceding chapter, short-lines may be designed either to prevent or to favor radiation. In the latter case they are called short-antennas, while in the former they are called linear-circuits (sometimes " feeders "). In practice, both types are operated in the resonant rather than the non-resonant condition.