TRANSMISSION LOSS DUE TO EESONANCE OF CONVERTED MODES 903 



ATTENUATION OF SPURIOUS MODE IN DECIBELS 



Fig. 3 — • Relative insertion loss as a function of the spurious mode attenuation 

 and mode conversion level. 



attenuation is low, but the general interpretation of the phenomenon is 

 still the one given above. 



From (6) we can calculate the extreme values of | r | differentiating 

 with respect to I, and we define the relative insertion loss I in db, as the 

 ratio between the minimum and maximum transmitted power expressed 

 in db. 



7 = 20 log 



10 



i min 



r 



■•■ max 



= 20 logio ^ 



1 



2 1 ri2 Kl + cosh at) 



1 - c' I r 



22 



2 —2a'>t 



1 - 



2|ri2|2(l - cosha^) 



(9) 



l + B'\ r22 Ye 



2 — 2a2^ 



where 

 E = 1 + 



ri2 



•l 22 



-at 



C 



1 - 



ri2 



i 22 



-a( 



a = ai — a2 



For the most important practical case, that is, when the maximum value 

 attainable by cosh aC is of the order of 1, and knowing from (3), (4) and 

 (5) that 



12 



ro2 r (1 - I ro2 p) 



r22 1' ^ 1 - 2 I ro2 



