FERRITES IN MICROWAVE APPLICATIONS 1347 



upon the diameter of the ferrite cylinder and upon the guide wavelengths 

 but not upon the length of the cylinder. 



Other waveguide effects causing anomalous loss behavior, such as 

 shown by curve G, have been discussed by Fox and Weiss" and \vill 

 be treated by them in greater detail in a forthcoming publication. 



In order to discuss these effects more fully we must examine the modi- 

 fications of the plane wave theory which must be made to explain the 

 behavior of a ferrite in a waveguide. 



WAVEGUIDE THEORY, LONGITUDINAL FIELD 



When a piece of ferrite is placed in a waveguide and magnetized it is 

 necessary to modify the foregoing plane wave theory to describe the 

 behavior of a wave passing through the ferrite. Because of the anisotropic 

 nature of the magnetized ferrite it is necessary to obtain a solution to the 

 specific problem of the waveguide containing the ferrite. When the mag- 

 netization of the ferrite precesses about the applied dc field it sets up 

 components of h which do not exist in any of the classical modes, and 

 unless one can deal with small perturbations the solution becomes quite 

 involved. 



The modes which can exist in the ferrite will often resemble the clas- 

 sical modes so that for convenience we will refer to them as modified 

 TE or TM modes. Suhl and Walker^^ have obtained solutions for the 

 case of a cylindrical waveguide completely filled with a magnetized 

 ferrite, and they have shown that the modified dominant TEn mode 

 behaves much like the plane wave in the region of small fields but that 

 the behavior of the TM modes cannot be approximated by a simple 

 extension of the plane wave theory. A waveguide large enough to sup- 

 port the dominant mode when filled with air will, when filled with ferrite, 

 support three or four higher order modes including some of the modified 

 TM modes. In this case, it is possible to have several present at the same 

 time with the result that observations of rotation, loss and ellipticity 

 are almost impossible to interpret. Accordingly, we should reduce the 

 size of the waveguide in the ferrite-filled region, and this involves the 

 creation of discontinuities in the waveguide. This is not always necessary, 

 however, because higher order modes will not always be set up in the 

 ferrite even though the waveguide is large enough to propagate them. 

 If care is taken to avoid geometries which favor a given mode the prob- 



" A. G. Fox and M. T. Weiss, Revs. Mod. Phys., 26, p. 262, Jan., 1953. 



12 A preliminary report of this work has been published in the form of a Letter 

 to the Editor by H. Suhl and L. R. Walker in Phys. Rev., 86, p. 122, 1952. A more 

 detailed account is scheduled for publication in the J. Appl. Phys. 



