Minimum noise figure for magnetron injection guns

A minimum noise figure has been derived for the magnetron injection gun. This theoretical expression is based upon RF equations which were developed to calculate the transport of current and velocity fluctuations along a planar 3-dimensional space-charge flow. Current and velocity fluctuations at the magnetron gun output were found to be correlated regardless of the assumed cathode conditions. The resultant minimum noise figure expression incorporating correlation is valid for any planar, lossless O-type device utilizing a magnetron injection gun. The variations of magnetron gun-velocity fluctuations, current fluctuations, and minimum noise figure versus transit angle and cathode-magnetic field angle were plotted assuming that the noise at the potential minimum consisted of the traditional values of uncorrelated shot current and mean-square velocity fluctuations. The noise figure for the other values of the dc magnetron-gun parameters and assumed cathode-noise conditions are easily calculated since all expressions are in closed mathematical form. Comparisons between this theoretical minimum noise figure and the noise performance of an operational multicavity klystron were made.