Topics in Guided Wave Propagation Through Gyromagnetic Media: Part III - Perturbation Theory and Miscellaneous Results

Parts I and II of this paper were devoted to a number of specific propagation problems, whose solutions, though frequently quite complicated, could be discussed with a reasonably modest investment of effort. Unfortunately, not all of these problems pertain to situations met with in actual gyromagnetic devices. Actual devices frequently employ structures whose performance could be predicted only as the result of lengthy computing programs. For example, the microwave gyrator using Faraday rotation usually employs a ferrite sample whose cross-section only partly fills that of the cylindrical waveguide. Although it is easy to formulate the corresponding equation for the propagation constant, the classification and surve}'", let alone the computation of solutions, would be very difficult to carry out. Thus, one must often be content with approximate results, and the bulk of the present paper is devoted to perturbation methods. These take as starting point a situation whose propagation problem is essentially solved. The small change in propagation constant due to a slight change in the original state of the system is then calculated. The small 1133