Antennas and Open‐Wire Lines. III. Image‐Line Measurements

摘要

A new type of open‐wire line is described for which many disadvantages, notably radiation and unbalance, are overcome by replacing one of the physical conductors by the image of the other in a semi‐infinite, highly conducting plane. The characteristics of a line driven at both ends and loaded at the center are examined; it is shown that the impedances measured on both sides of such a line are equal and simply related to the load impedance, provided that electrical symmetry is maintained about the load point. The double‐ended drive requires no dielectric supports and permits the line conductor to continue past the load. The construction and operation of an image line with double‐ended drive is described. The characteristics of the new line compare very favorably with those of a good coaxial measuring line. Finally, use of the line in the measurement of the apparent impedance of a cylindrical dipole antenna as a function of the line spacing is described.