Monte Carlo Calculation of Noise Near the Potential Minimum of a High-Frequency Diode

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Abstract
Noise near the potential-minimum of a high-frequency diode has been calculated in this paper using a high speed electronic, digital computer. Random numbers were generated and used to simulate the emission of electrons at the cathode. Electrons emitted were continuously fed into the calculating process and those collected on the anode or returned to the cathode were automatically erased. In this way the electron motions computed by numerical integration followed the actual operation of a one-dimensional space-charge limited diode. The results of this paper are based upon data obtained in the course of 3000 unit time intervals. In each case current and velocity fluctuations near the potential minimum were computed. This basic information permitted the calculation of the reduction in noise current caused by space-charge smoothing. The results were then applied for a calculation of the minimum noise figure for microwave beam-type amplifiers and show a sharp minimum of less than 2 db around 2500 Mc and a maximum of about 7.5 db near 4000 Mc. At very low frequencies the noise figure is small and agrees with existing low-frequency theories. At very high frequencies it approaches the figure corresponding to full shot noise, namely 6.3 db. Within the accuracy of calculation, correlation between current and velocity fluctuations has not been found nor the smoothing in velocity fluctuation.

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