Modeling Vacuum Electronic Devices Using Generalized Impedance Matrices
We have developed a general approach to modeling a large class of vacuum electronic devices (VEDs) by using impedance matrices to characterize the circuit structure. Our approach can treat VEDs that have an arbitrary number of interaction gaps, severs, and input and/or output ports that may incorporate arbitrarily complex matching and/or tuning elements and windows. To find the impedance matrix for a given structure, we use the computational electromagnetics 3-D finite-element code HFSS to compute the response of the entire structure to an excitation of each individual port and gap. We define voltages and currents as certain integrals over the electric and magnetic fields, respectively, the ratios of which are elements of the generalized impedance matrix. This matrix is then imported into a beam-wave interaction code, which is used to compute VED performance (gain, output power, bandwidth, and so on). We have implemented this capability in a new 2-D code TESLA-Z, which has been verified by comparison with the large-signal code TESLA-FW and then validated by comparison with measured data from a Ka-band folded-waveguide power-booster TWT. Similar capability was also implemented in the 1-D interaction code CHRISTINE-CC.