ADMITTANCES OF PARALLEL-!' LANE ELECTRON TUBES 



621 



these effects experimentally. It seemed best to start this work with a study 

 of the electron stream admittances of simple diodes, with the object of 

 extending the measurements to the triode as the work progressed. 



Diodes 



Tlie diodes used in this work were identical in construction with the 155,^ 

 triode, Inil for the substitution of a solid copper anode in place of the grid. 

 Tn all cases the cathode-anode spacing was approximately 0.65 mil, and the 

 area of the cathode was 0.164 square centimeters. With this spacing one 

 would expect the potential minimum to be relatively close to the anode such 

 that a considerable portion of the cathode-anode region would contain 

 electrons moving in both directions. The potential distribution then would 

 be something like that shown in Fig. 2. 



Fig. 2 — Electron motion in a close-spaced diode. 



The method used in measuring the microwave-frequency input admit- 

 tances of diodes was based largely on a technique used by Mr. J. A. Morton, 

 and will be described in some detail. 



In a typical amplifier, radio-frequency power is fed from a waveguide 

 source to the cathode-grid input region of a 1553 triode through a waveguide- 

 cavity transformer. A similar circuit can be used for measuring diode ad- 

 mittances. The fundamental problem is to learn how to relate admittances 

 measured with a standing wave detector located in the wa\cguide supply 

 line to the equivalent two-terminal admittances located at the cathode- 

 anode gap of the diode itself. In other words, we have to know the trans- 

 formation-ratio between an admittance across the cathode-anode gap of the 

 diode and the corresponding admittance which will be measured in the 

 waveguide. 



Let us refer to the circuit in Fig. 3. The circuit shows an input trans- 



