Traveling-wave tube oscillators

Theory is presented for a traveling-wave (or other wave) tube oscillator, with emphasis on the maximum range of electronic tuning which can be obtained. Experimental data on two traveling-wave tube-oscillators is given. A very simple arrangement consisting of a traveling-wave tube with feedback through an external path which includes a transmission cavity filter yields a tuning range of 4 to 8 percent with changes in helix voltage, according to theory. 4.5 percent has actually been obtained. The tube should be short since relative mode separation is of the order of half the reciprocal of the number of periods about the complete feedback loop. It should also have a high gain per unit length since the total electronic tuning range is estimated to be of the order of three-fourths the Pierce gain parameter C. Normal dispersion in the tube or external path acts to decrease mode separation; dispersion unavoidably associated with a transmission cavity filter has been included in the above figures and reduces the tuning range to about three-fourths what it would be with a hypothetical dispersion-free circuit. A more general analysis in terms of the transmission parameters of the system in matrix form is included.