400 THE RELL SYSTEM TECHXTCAL JOURXAL, MARCH ] 9o7 



low and a high vahie of tran.sfcr loss as indicated b\' (14) which repre- 

 sents the forward traveling coupled wave amplitude where ex is the total 

 coupling strength/ 



^-,^/(..^.o.,/-'"[/^^^i^^^1" 



(14) 



At midband ex = tt 2 and experience has shown .r = 10 Xn ; therefore 

 c = 7r/20Xo at midband. The coupling hole radius is found from (3). 

 Because longitudinal slots are used instead of round holes the equivalent 

 hole radius r is found from fr^ = P(^, where P is the magnetic polariza- 

 bility' and ( is the length of the chosen slot. To avoid slot resonance in 

 either band, the length was chosen to be approximately Xci/4 in the 

 6-kmc band and fX,) in the 11-kmc band. The power expression of (3) 

 must be corrected by the wall thickness effect (4) and also multiplied 

 by the factor F due to the presence of the dielectric .slab' (15). 



7ri3n\a[Ki{di - \ sui 20i) + A^K.id. - \ sin 2^2)] 



B. = KM - d) e. = M A = (^pYs^^ 



XKo/ cos 60 



Theoretical coupling lo.ss per hole is defined by 



20 logio a = 10 log ^- - (A + 10 logio F) , (16) 



i 1 



An additional correction which reduces the coupling loss is due to the 

 long length of the slot. Although the slot resonates near 9 kmc, an in- 

 crease of 3 db in a single slot coupling results at 6 kmc. This effect was 

 found experimentall}' from a sample test line with several slots. To avoid 

 excessive length two rows of coupling slots were employed. The}' were 

 staggered to impro^'e the continuity of coupling from discrete points. 

 An approximate design is on hand at this point. The final dimensions 

 for the guides and coupling holes are found after the perturbations of the 

 phase constants are considered by the same process as noted in the dis- 

 cussion of the 11-kmc design. Impedance matching for the dielectric 

 strip and the coupling slot array was patterned after the technique 

 shown for the coupling hole array in the 11 kmc design. 



