CALCULATION OF BEAM LOADING USING THE INDUCED-CURRENT METHOD IN PASSIVE CAVITIES

Quantitative knowledge of beam loading and detuning is necessary for the prediction of the bandwidth and operating frequency of an electron device that has resonant interactions. We present a method for calculating the loaded Q and beam detuning of a passive (gain or idler) cavity in an electron device. The method is based on the determination of induced current by a technique often referred to as Ramo's theorem. We use the induced current in conjunction with a lumped equivalent circuit representing the cavity. This leads to a solution for the self-consistent cavity fields. Although the induced-current expression is usually developed from low-frequency models, we show that Ramo's theorem is valid for high-frequency, steady-state analysis when the unloaded passive cavity Q is high. We use the method to calculate the loaded Q of the passive cavity of a new type of gyro-resonant electron device, the magnicon.