Traveling-wave tube devices with nonlinear dielectric elements

The performance of traveling-wave tube (TWT) amplifiers incorporating nonlinear dielectric elements is studied via computer simulation. Two different situations are investigated: (1) the use of nonlinear dielectric elements to reduce intermodulation distortion and (2) the use of voltage-controlled dielectrics to provide rapid modification of the dispersion characteristics of the slow-wave structure. In the first case, the use of dielectrics with negative second-order susceptibilities is studied as a means of reducing phase and intermodulation distortion. Use of these dielectrics along with dynamic velocity taper to reduce amplitude modulation distortion results in marked reduction of predicted intermodulation distortion. In the second case, the goal is to design an amplifying structure whose gain as a function of frequency can be varied electrically. Preliminary design studies show that relatively large changes in the center frequency of the amplification band can be achieved with relatively modest changes in the dielectric constant of helix support structure.