NATURE OF POWER SATURATION IN TRAVELING WAVE TUBES 845 



Table I 



* At Bell Telephone Laboratories. 



t Reference 10 (a slight beam misalignment could account for most of this 

 difference). 



t Siemens & Halske, Munich, Germany. 

 § Telefunken, Ulm, Germany. 



and of the gain parameter, where efficiency is proportional to C, as ex- 

 pected from small-signal small-C predictions. This reduces the problem 

 to a determination of -q/C versus QC and 7ro . 



Many measurements of this kind have been made, and the data are 

 summarized in Figs. 2 and 3, with efficiency shown as a function of QC 

 and yro . In Fig. 2 we have the efficiency when the beam voltage is that 

 which gives maximum low-level gain. Fig. 3 shows the efficiency ob- 

 tained when the beam potential is raised to optimize the power output, 

 and contours of constant efficiency have been sketched in. There is 

 significantly higher efficiency than before in the region of maximum effi- 

 ciency, but not much more elsewhere. 



Fig. 4 shows how efficiency varies with C for a small value of QC, a 

 representative value of 7ro , and with beam voltage increased to maxi- 

 mize the output. This indicates a maximum of about 38 per cent at 

 C = 0.14. 



Some of the computed results of Tien, Walker and Wolontis, and of 



Tien are also indicated in the figures. Their results generally indicate 



somewhat greater efficiencies than were observed, but in the most sig- 



i nificant region the comparison is not too bad as will be seen in a later 



section. 



The measurements are for conditions having negligible circuit loss 

 near the tube output. There are no new data on the effect of loss, but 

 earlier results'** have been verified by measurements at Stanford Uni- 



versity and are still believed to be a satisfactory guide in tube design. 



