THE FIELD DISPLACEMENT ISOLATOR 



887 



top and bottom faces of the ferrite and approach, in a sense, a less critical 

 rod type geometry. A ferrite height of 0.550" gave a VSWR -^ 1.05 

 (iver the band. With full height slabs (0.795"), A^SWR values as high 

 as 10:1 have been observed for typical geometries. 



I j C. 8 and h 



Experimentally, we have examined various ferrite thicknesses at dif- 

 ferent distances from the sidewall until optimum broadband performance 

 . jwas obtained. Table I shows the ferrite distance from the wall which 

 • I gave the best experimental results (highest broadband ratios, low for- 

 ,ward loss, high reverse loss) for each thickness 8 of one of the BTL 



I materials. It is interesting to note that the empirical ctuantity 8 -\- 6/2 — 



I 



Table I 



2t, where t is the thickness of the resistive coating, is very nearly con- 

 stant (within a few mils) for the stated range of 8 and for this type of 



[design.* 



i In Section IV a theoretical calculation using the null condition at 



i 6175 mc/sec for a full height ferrite gives 



5 = 180 mils 



b = 38.7 mils 



so that 8 -f b/2 = 199.3 mils. In the theoretical case t is assumed to be 

 very small. It will be noted that the theoretical result for 8 + b/2 (with 

 small t) agrees quite well with the experimental 5 -f 6/2 — 2t. The ques- 

 tion of the possible phj^sical significance of this quantity is being 

 investigated. 



D. Placement of Resistance Material and Choice of Resistivity 

 The propagating mode with a full height ferrite slab is of a TEo 

 variety, the zero subscript indicating that no variation occurs with re- 



* In one design of the isolator we used a General Ceramics magnesium manga- 

 nese ferrite with 5 = 0.180", b = 0.074" and t = 0.009" so that 8 + b/2 - 2t = 199 

 mils, in good agreement with Table I. 



