FERRITES IN MICROWAVE APPLICATION'S 1351 



wave theory. Experimentally one will observe very erratic and fre- 

 quency-dependent behavior under these conditions. 



WAVEGUIDE THEORY — TRANSVERSE FIELD 



A waveguide, either round or rectangular, filled with ferrite and mag- 

 netized by a field parallel to the electnc vector of the dominant mode 

 will exhibit a behavior qualitatively the same as described in the plane 

 wave theory of the transverse field. In fact, it has been shown that in a 

 rectangular guide all of the TEo^ modes can exist with only slight modi- 

 fication.^^ That this result is probable may be seen from the fact that the 

 precessing magnetization vector sets up components of h in the x and y 

 directions when the applied field is in the z direction, and both of these 

 components normally exist in the TEon modes. The primary modification 

 of the mode arises from RF demagnetizing fields in the ferrite. Because 

 of this modification it is extremely difficult to match the boundary con- 

 ditions for normal incidence at an interface between the ferrite and air 

 in the waveguide. An infinite series of modes is actually required, but 

 in practice the mismatch due to magnetic effects is usually not very large. 

 If one matches the dielectric constant by means of tapered dielectric 

 horns the remaining mismatch is slight except where ti^u approaches 

 zero and at resonance. 



While the completely filled waveguide magnetized by a transverse 

 magnetic field parallel to the electric vector of the wave will exhibit a 

 reciprocal behavior in respect to phase change and attenuation, an in- 

 teresting and potentially useful modification of these effects occurs when 

 a small piece of ferrite is located asymmetrically in a waveguide. Chait 

 and Sakiotis^^ of the Naval Research Laboratory and Turner of the 

 Holmdel laboratory of Bell Telephone Laboratories have independently 

 observed a phase shift which is dependent upon the direction of propaga- 

 tion of the wave, and a simple explanation of this effect has been made by 

 Turner^ ^ and by Kales. ^^ Suhl and Kales^^ have shown the theoretical 

 validity of this explanation. The idea can be demonstrated by considera- 

 tion of the field configuration shown in Fig. 9. 



An observer at the point P will see an h field which is elliptically po- 

 larized in a plane normal to the direction of Ha- The sense of the rotation 

 of the larger circular component of the ellipse will depend upon the 

 direction of propagation of the wave. Thus for one direction the major 



^''A A. van Trier, Paper presented orally at meeting of Amer. Phys. Soc., 

 Washington, D. C, April, 1952. 



16 M, L. Kales, H. N. Chait and N. G. Sakiotis, Letter to the Editor, J. Appl. 

 Phys., June, 1953. 



16 E. H. Turner, Letter to the Editor, Proc. I. R. E., 41, p. 937, 1963. 



