1400 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



For the above case C = 5.7 X 10" farads or l/coC at 5.4 millimeters 

 is about 50 ohms. 



The accuracy of this capacitance calculation can be verified later 

 when a completed rectifier is measured for its high frequency conversion 

 loss. This is possible because we know the calculated low frequency 

 conversion loss of the rectifier, for the case of zero spreading resistance 

 from Southworth's book. Fig. 12.3-7. For an exponent of four this loss 

 is given as 4.4 db. The additional loss at high frequency due to the 

 capacitance, C, may be calculated (see Equivalent Circuit II) by the 

 formula : 



Additional Loss 



10 logic :?L+_?f db 

 /ti 



(2) 



From the text (Fig. 8), it is seen that the average wafer rectifier unit 

 has a conversion loss at 5.4 millimeters of 7.2 db; thus, the difference 

 between the low and high frequency conversion losses is very nearly 3 db. 

 This means that about one-half the signal power is lost in the spreading 

 resistance; hence Ri and i?, are about equal. By transferring back to 

 Equivalent Circuit I, the average value of the capacitance is found to be 



4.1 X 10 farads, which is a reasonable check with the calculated value 

 given by (1). 



Inductance of the Contact Spring 



The remaining parameter of the equivalent circuit to be determined 

 is the inductance of the contact spring. The value of the equivalent 

 parallel resistance, i?2 , depends on the inductance L (the other param- 

 eters being fixed), or conversely, for a given value of R2 , the appropriate 

 value for L may be calculated from the formula for Equivalent Circuit 

 III. For an off-center match of the rectifier to the waveguide, R2 must 

 equal the guide impedance, Zd , at the rectifier location. Also, for a 

 match, the distance, I, from the rectifier to the waveguide piston must 



'/////////////////////////////J///////////////////^///////A 



'R'. 



I 



PISTON 



V////////////////////////////^///////////////////////>////////. 

 WAVEGUIDE B| J 



T 



I 



b 

 I 

 I 

 I 



i_ 



V///y^////y'y'//J///////////////77777y 



I 



V///////////f////y/////////y/y7/77/A 



k 



. -A 



Fig. 14 — Mulching circuit for rectifier offset in waveguide. 



