Drive signal frequency multiplication in a hybrid antenna-amplifier device

Summary form only given. It was proposed that a traveling wave tube could be combined with a surface wave antenna if a relativistic electron beam propagates near and along the antenna´s slow-wave structure. In such a hybrid antenna-amplifier device, the TWT RF drive would simultaneously serve as the antenna feed signal. In the cylindrical geometry of the hybrid antenna-amplifier, the annular beam propagates outside a rod antenna, and the operating mode is the fundamental non-axisymmetric mode. In this paper, an important feature of this device following from the nonlinear multi-mode consideration is described, namely, the possibility of the generation of harmonics due to the fact that multiples of the fundamental mode amplification band frequencies may lie within the amplification bands of the higher-order modes. We have simulated the system using the set of equations similar to that from nonlinetuning schemesar TWT theory, but taking into account an arbitrary number of modes capable of interacting with an electron beam due to the TWT mechanism, as well as accounting for the azimuthal asymmetry of RF fields. Non-synchronous AC space charge fields are neglected. We used the actual values of mismatch and Pierce parameters calculated for different modes of the circular waveguide with an inner dielectric rod. At certain, parameters, the output power level at the second or third harmonic can significantly exceed that of the main frequency, distinguishing this system from a classical TWT with a very large bandwidth. Further, novel tuning schemes can be achieved. It has also been found that the character of field growth at harmonics of the main frequency significantly depends on whether the input signal field structure is fixed or azimuthally rotating. In addition to the modeling, we present simulation results obtained using the 3-D version of the MAGIC code to verify the existence of the effect discussed above.