78 BELL SYSTEM TECHNICAL JOURNAL 



The input standing wave ratio on the input Hne is given by 



Oq -+- 02 



The leakage power is similarly given by 



Pr = Po 52 (14) 



while the gas-discharge power in terms of these parameters and the power 

 in the transmitting line (P) is given by 



P, = (P Po h?"" (19) 



The parameters 5i and ^2 are properties of the input and output coupling 

 as they are geometrically related to the cavity and are substantially in- 

 dependent of the Q of the cavity. The parameter 5o is, however, the recipro- 

 cal of the intrinsic or unloaded cavity Q. Equation 12 is seen to depend 

 upon 5o but equations (14) and (19) do not. The efifect of variations in 

 Q is thus demonstrated. 



The over-all performance is also affected by the relative values of 5i 

 and 62. In view of the dependence of Pr on b-2 directly and on 5i indirectly 

 through the fact that Po is not entirely independent of Pg, it is advantageous 

 to adjust the values of 5i and ^2 so that the input standing wave ratio (o- of 

 equation 13) is unity. Such a condition is also very desirable for system 

 reasons as well. When this condition is met, equation (12) reduces to 



J, _ ^2 



The curve marked o- = 1 of Fig. 15 and the curve of Fig. 16 were plotted on 

 this basis. It should be noted that matched input requires that the input 

 window be larger than the output window. 



TR boxes are unfortunately not always operated in the in-tune condition, 

 and they must also pass a band of frequencies as fixed by the narrowness of 

 the transmitter pulse. For these reasons the Q must not be set at too high 

 a value. The additional low-level loss which results from off-tune operation 

 may be computed from equation 28 of appendix A. 



Incidentally, it is an experimental fact that the leakage power and the 

 gas-discharge power are not materially altered by small departures from the 

 in-tune adjustment, presumably because of the very low effective Q of the 

 gas discharge. 



The ATR Low-Level Loss Component. The component of low-level loss 

 which results from losses of power to the transmitting branch depends very 

 greatly upon the "cold impedance" of the magnetron or other transmitting 

 tube and upon the properties of an ATR box if one is used. As shown in 



