Stability of Negative Impedance Elements in Short Transmission Lines

Abstract

Until recently, voice frequency repeaters of the two-way type have been applied almost exclusively to electrically long transmission lines. Now, negative impedance repeaters are used in quantity in the exchange telephone plant, and applications to electrically short lines arise more frequently. Because lower over-all transmission losses can be obtained by utilizing the lower phase shift in short lines, a different engineering approach to the application of E-type negative impedance repeaters is desirable. This paper outlines a general method whereby transmission performance and stability can be related to the characteristics of a symmetrical repeater located in the center of a short transmission line. The theory is particularly applicable to negative impedance repeaters. A tandem arrangement of short sections of transmission line, where each section has a centrally located repeater, can be classed as a line loaded with negative impedance.