Antenna and Feeder Mutually Self-matching

Author: Edmund A. Laport

This method (Fig. 4.29) consists in constructing the antenna for its desired radiation properties, then measuring or carefully computing its input resistance, and using a feeder with a characteristic impedance equal to the input resistance of the antenna. The antenna can often be designed to have the proper radiation characteristics and also have an input impedance of a desired predetermined resistive value, to match directly a preferred type of feeder. Examples of this technique are the folded dipoles, folded uni-poles, and multiple-tuned antennas. The principle may be applied in a number of ways in many different kinds of systems. In very-high-frequency and ultrahigh-frequency techniques it is frequent practice to design the antenna input impedance to match that of a preselected type of feeder. Figure 4.30 exhibits two cases where an impedance match can be realized by using only one reactive element.