Intermodulation in klystrons and TWTs

Summary form only given. Intermodulation is of great concern in communication applications of microwave tube amplifiers. High channel density is desirable and output linearity is important, particularly in digital systems. Predistortion and backing off the output power are both costly remedies. Accurate modeling of intermodulation would promote understanding of this phenomenon and allow mitigation schemes to be evaluated. A recently developed theory of klystron intermodulation provides a simple algorithm to compute the intermodulation products and harmonics to all orders, for an arbitrary number of RF input signals. Here, we compare the theory with experiments and investigate the spectrum arising from non-balanced drive signals. We also provide the mathematical proof that the algorithm fully accounts for charge overtaking. The klystron intermodulation theory is being extended to the TWT; it is formulated in such a way that for single frequency drive in the small signal regime, the algorithm exactly reproduces Pierce´s linear theory, including his account of the launching loss. Preliminary results of the relatively simple algorithm include the computation of thirdand fifth order intermodulation products for drive signals at 5.0 and 5.1 GHz and we find qualitative agreement with the well-established Christine code. Ongoing attempts to improve the theory to saturation will be reported.