The Use of Negative-Impedance Units Inserted Uniformly Into a Transmission Line to Reduce Attenuation

Abstract

This paper describes the general properties of a negative‐impedance‐boosted (NIB) transmission line, an otherwise uniform line to which lumps of negative impedance have been introduced periodically along its length. The purpose of these lumps is to reduce the attenuation of the line, but they also make possible self‐oscillation and cause reflections. However, these reflections are cancelled up to a cutoff frequency that has an inverse relationship to the spacing of NIB units. Summaries are included of the latest NIB project; of previous investigations into NIB lines, many of which were not published; and of the first work in the Bell System to reduce transmission‐line attenuation through the introduction of loading coils and then unilateral amplifiers. It is shown that many of the differences between properties of NIB lines and properties of a line fitted with unilateral amplifiers come from the different ways the source of energy replenishment is coupled into the line. It is shown that, under suitable conditions, the addition of small simple NIB units to a transmission line can reduce its loss to a low level in a stable manner and also equalize it. Because of some properties of NIB lines, they cannot be used successfully in all situations; in particular, an environment in which large longitudinal currents are induced in the lines is unfavorable.