Topics in Guided Wave Propagation 

 Through Gyroniagnetic Media 



Part 111 — Perturbation Theory and Miscellaneous Results 



By H. SUIIL and 1.. R. WALKER 



Some prohlcnif^, complete discussion of which would be extremely difficult, 

 are treated approxijnately by means of perturbation theory. Among these 

 are the partially filled cylindrical waveguide, and the problem of multiple 

 internal reflections in a sample of finite length filling the cross section of a 

 cylindrical guide. Propagation in a ferrite between pai'allel planes, mag- 

 netized along the propagation direction is discussed by the methods described 

 in Part I. The paper concludes with an addendum to Part I — a numer- 

 ical study of field patterns of the TEu-limit and TMn-limit mode for 

 various dc magnetic fields. 



IXTRODUCTIOX 



Parts I and II of this paper were devoted to a number of specific propa- 

 gation problems, whose solutions, though frec^uently quite compHcated, 

 could be discussed with a reasonably modest investment of effort. Un- 

 fortunately, not all of these problems pertain to situations met with in 

 actual gyromagnetic devices. Actual devices frequently employ struc- 

 tures 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 classifica- 

 tion and survey, 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 essen- 

 tially solved. The small change in propagation constant due to a slight 

 change in the original state of the system is then calculated. The small 



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