FERRITES IN MICROWAVE APPLICATIONS 1367 



frequency the dc magnetic field was adjusted so that absorption was a 

 maximum for the wave for which the absorption is the greater. The 

 field was then reversed and the absorption was again measured. Since 

 reversmg the field is entirely equivalent to reversing the direction of 

 propagation we obtain in this way the insertion loss for both directions 

 of propagation. Data taken in this manner are shown in Fig. 22 along 

 with a sketch of the geometry employed. The VSWll was measured in 

 the case of the thinnest plate and was found to be less than 1 05 to 1 

 over the band. The variations in the dotted curve, however, are probably 

 due to reflections from the ends of the sample. 



One must bear in mind that as the frequency is changed, the field 

 required for ferromagnetic resonance is changed so that these data do 

 not give a true index of the bandwidth of the device. This must be 

 measured at a constant value of field. However, if we had used a ferrite 



36 



32 



28 



§ '6 



CD 

 < 



6200 



6400 6600 6800 7000 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 21 — Absorption of forward and reverse waves at the optimum value of 

 field as functions of frequency. Two sample thickness are shown to illustrate the 

 effect of sample thickness. 



