Noise factor of a transmission line subjected to thermal gradients

A novel, analytical treatment of noise factor in ideal transmission lines subjected to thermal gradients is presented. Temperature dependence on the propagation direction is assumed linear, whereas line loss is initially considered constant. The latter restriction is then removed, in such a manner that, for the first time in the literature, linearly varying line losses are also addressed. In both cases, closed formulae are presented allowing to compute line noise factor for arbitrary source terminations. Previous numerical implementations of the underlying theory are also reappraised both as an introduction to the Reader and as a test bench of the closed-form results. A discussion of the effects of a non-uniform temperature distribution across the transverse section of the transmission line is provided upfront, so as to clarify the conditions under which the usual simplifications are valid. This discussion too is believed by the Authors to be original.