FERRITES IN MICROWAVK A IMM.K \ ri()\> 13()5 



netized. Since these latter effects are quite new two measurements of 

 this type are shown to illustrate the sort of performance obtainable. In 

 the first experiment a' slab of ferrite 20 mils thick was placed successively 

 in several positions in a rectangular w^aveguide, and the phase shift as a 

 function of field was measured for both directions of propagation. When 

 the plate of ferrite is centrally located the phase shift is the same in both 

 directions but when the ferrite is placed half way between the center and 

 the edge of the guide a large difference in phase shift is observed. Finally 

 when the slab of ferrite is located at the edge of the guide there is only 

 a small difference between the positive and negative phase characteris- 

 tics. This small difference will vanish as the thickness of the ferrite plate 

 goes to zero. In Fig. 21 (a) we show the phase shift versus applied field 

 for three positions of the ferrite slab and in Fig. 21 (b), the differential 

 phase shift at a constant value of applied field is plotted against the posi- 

 tion of the ferrite plate. The solid line curve taken at 9,500 mc indicates 

 that maximum differential phase shift is obtained when the ferrite is 

 located approximately 0.100'' from the guide wall. Suhl's prediction is 

 that the position at w^hich maximum differential phase shift is observed 

 should be independent of frequency. The dotted curve in Fig. 21 (b) 

 taken at 8,200 mc verifies this part of the prediction in that the maximum 

 again occurs where the ferrite plate is 0.100" from the guide wall even 

 though the point at which h is circularly polarized has been shifted sig- 

 nificantly by the change in frequency. 



The second measurement was designed to measure the non-reciprocal 

 absorption which is obtained when the strength of the dc magnetic field 

 is adjusted so that the ferrite is at ferromagnetic resonance. In order to 

 obtain the minimum forward loss and maximum reverse loss it is essential 

 that the ferrite be located precisely at the point where the transverse 

 and longitudinal components of the h field of the wave are equal, i.e., 

 where the h field is circularly polarized in a plane perpendicular to the 

 magnetic field. Since this condition exists at only one point in the half- 

 waveguide the ferrite slab must be made very thin. Measurements were 

 made in the 6000-7000 mc band in RG50 w^aveguide. A thin plate of 

 "Ferramic G" was cut so as to extend from one broad wall to the other 

 Its length w^as approximately 1-}^'' and its thickness was originally 

 0.050" and was subsequently reduced to 0.025" and finally to 0.009". 

 In the last case the ferrite was so fragile that it was necessary to support 

 it by cementing it to a }i-mch plate of polystyrene. For convenience the 

 ferrite plate was fastened securely in place at a point calculated to be 

 the point where the h vector is circularly polarized at the center of the 

 band, and frequency was varied about this center frequency. At each 



