Suppression of Third-Order Intermodulation in a Klystron by Third-Order Injection

The first observations and measurements are reported on suppression of the third-order intermodulation (IM3) product arising from nonlinear mixing of two drive frequencies in a klystron, by externally injecting a wave at the IM3 product frequency. Optimum amplitude and phase of the injected wave for maximum suppression are examined. Results indicate that suppression of the IM3 product by as much as 30 dB can be achieved. Experimental results compare favorably with predictions of a 1D simulation code that takes into account all kinematical and dynamical effects including charge overtaking and space charge forces.

Figure 1

Klystron small signal gain versus frequency.

Figure 2

Klystron drive curve (input power versus output power).

Figure 3

Schematic of the experimental circuit.

Figure 4

Output spectra of the klystron with the two fundamental drive waves and the self generated IM3.

Figure 5

(a) Sensitivity of the IM3 suppression to variation in injected IM3 phase with respect to the fundamentals; (b) Expanded view of the region around maximum suppression.

Figure 6

Sensitivity of the IM3 suppression to variation in injected IM3 amplitude.