The Production of Ultra-High-Frequency Oscillations by Means of Diodes

HE theory of the production of negative impedance by means of an electron discharge between two parallel planes has been known for some years. 1 The negative resistance appears whenever the electron transit time is approximately V/i, etc. cycles of a given high-frequency current. Using this property, Miiller was able to construct tubes giving 100 cm. oscillations.2 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.