The Character of Waveguide Modes in 

 Gyromagnetic Media 



By H. SEIDEL 



(Manuscript received August 31, 1956) 



A magnetized gyromagnetic medium is birefringent. The effect of bire- 

 fringence is studied in rectangidar and circular waveguides with special 

 attention paid to propagation characteristics in guides of arbitrarily small 

 cross-section. Propagating , small-size structures are found in certain ranges 

 of magnetization for both types of guide. 



I. INTRODUCTION 



A gyromagnetic medium, isotropic in the absence of a magnetizing 

 field, becomes axially symmetric with respect to that field when mag- 

 netized. A tensor susceptibility^ is thus produced which reflects the 

 resulting anisotropy. Two essentially different types of rays appear in 

 the medium in much the same manner in which the ordinary and extra- 

 ordinary optical rays form in a calcite crystal. These rays may combine 

 to produce results in a ferrite loaded waveguide quite alien in character 

 to those of a conventional isotropic guide. Since the ferrite is, to first 

 order, characteristic of general gyromagnetic media we shall discuss all 

 gyromagnetic phenomena in terms of ferrites alone. 



One very startling phenomenon observed in ferrite loaded waveguides 

 is the occurrence of propagation in a waveguide of arbitrarily small 

 transverse dimensions.- We shall show that this type of wave guide 

 behavior is a consequence of the particular form of the birefringent 

 character of the medium. 



In order to understand the nature of the ferrite loaded case let us first 

 consider the conventional isotropic small wave guide. Fig. 1 shows, 

 schematically, the field distribution encountered in a small rectangular 

 waveguide operating in a (1,1) mode. The .r axis is shown along the 

 wide transverse dimension and z is along the narrow height dimension. 

 The y axis is chosen to coincide with the guide axis. 



The field solutions of such a wa^•eguide may be obtained as a super- 



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