The Production of Ultra-High-Frequency Oscillations by 



Means of Diodes 



By F. B. LLEWELLYN and A. E. BOWEN 



The general problem of obtaining oscillations by the use of 

 diodes with critical electron transit time is outlined. Some of the 

 properties of a 10 cm. oscillator tested experimentally are included. 

 Extraneous losses were reduced when the oscillator was enclosed 

 within a wave guide. 



THE theory of the production of negative impedance by means of 

 an electron discharge between two parallel planes has been 

 known for some years. ^ The negative resistance appears whenever the 

 electron transit time is approximately 134. 23^^, 334, etc. cycles of a 

 given high-frequency current. Using this property, Miiller was able 

 to construct tubes giving 100 cm. oscillations.^ The operating 

 efficiencies were quite low, and in the frequency range covered by 

 these tubes it seems fairly conclusive that other methods of producing 

 oscillations are more effective than the critical transit time diode. 

 However, there is promise in the application of diode operation to 

 much higher frequencies than those of Miiller. 



In a diode where the electron discharge occurs between two parallel 

 planes where one performs the function of electron emitting cathode 

 and the other constitutes an anode biased at a positive potential, the 

 effective impedance presented to an external source is inherently low 

 in magnitude. This is because of the capacitance between the two 

 planes which causes the decrease in impedance at high frequencies. 

 For the production of oscillations, the capacitance must be combined 

 with a resonant structure having the proper inductance to resonate at 

 the desired frequency and having a resistance which effectively is less 

 in magnitude than that of the electron stream. Because of the low 

 losses thus required of the coupling or tuning circuit the properties 

 of concentric lines and of tuned cavities offer a favorable method of 

 attack. These structures also have the property that the impedance 

 presented to the diode proper may be made low to match its capacitive 

 reactance at the high frequencies desired. 



The two most important sources of circuit resistance are ordinary 

 ohmic loss modified in the usual way by skin effect in the conducting 



^ For numbered references see end of paper. 



280 



