Slow-wave structure (SWS) is a core part of a traveling-wave-tube (TWT) amplifier. In this letter, the planar microstrip meander SWS on a dielectric substrate at V-band (50-70 GHz) is studied. The basic electromagnetic parameters of the SWS are calculated. The SWS circuits are designed and fabricated, and good transmission characteristics are measured. The SWS developed is characterized by a wide bandwidth and a relatively-large slow-wave factor, and is suitable for a low-voltage TWT with the sheet electron beam.

Results of numerical simulation of a miniaturized sub-THz traveling-wave tube amplifier with sheet electron beam and planar grating slow wave structure (SWS) are presented. Cold characteristics of the SWS are calculated. Small-signal and large-signal gain regimes are studied by the 1-D parametric frequency-domain code. The results are verified by simulations using 3-D particle-in-cell codes.

This article presents the results of a design study of an electron-optic system (EOS) for a sheet-beam G-band traveling-wave tube. An electron gun providing a 0.1-A, 20-kV sheet beam emitted by a 0.8 mm x 0.8 mm curved cylindrical cathode is designed. The beam dimensions at waist position are 0.05 mm x 0.8 mm with a compression ratio of 16 in the vertical direction. A magnetic system providing 1.1 T magnetic field, which is nearly seven times higher than the Brillouin field, is designed, and beam transmission in the 0.1 mm x 0.85 mm beam tunnel is studied by 3-D particle-in-cell (PIC) simulation. It is demonstrated that the beam has a complex structure of particle distribution, i.e., a high-density central part (core) and a peripheral low-density part (halo). The effect of assembly tolerance on beam transmission is studied. The prototype gun is fabricated, which compresses the beam to 0.1 mm by electrostatic field only. The 135-mA current with 95% transmission through the 0.2-mm anode aperture is measured.

A nonstationary nonlinear model for numerical simulation of a coupled-cavity traveling-wave tube is described. The model is based on the nonstationary discrete theory of excitation of a periodic waveguide structure, when it is supposed that the beam-wave interaction takes place only inside the cavity gaps separated by drift spaces. Such an approach allows one to consider properly the dispersion of the slow-wave structure (SWS) and to simulate processes at any point inside the SWS passband, including interaction near cutoff and even beyond the passband. Results of numerical simulations of amplification in small-signal and large-signal regimes are presented. Self-excitation processes near cutoff frequency are studied. In particular, drive-induced self-excitation that takes place only in the presence of a sufficiently strong driving signal is discussed.

The application of chaos in communications and radar offers new and interesting possibilities. This article describes investigations on the generation of chaos in a traveling wave tube (TWT) amplifier and the experimental parameters responsible for sustaining stable chaos. Chaos is generated in a TWT amplifier when it is made to operate in a highly nonlinear regime by recirculating a fraction of the TWT output power back to the input in a delayed feedback configuration. A driver wave provides a constant external force to the system making it behave like a forced nonlinear oscillator. The effects of the feedback bandwidth, intensity, and phase are described. The study illuminates the different transitions to chaos and the effect of parameters such as the frequency and intensity of the driver wave. The detuning frequency, i.e., difference frequency between the driver wave and the natural oscillation of the system, has been identified as being an important physical parameter for controlling evolution to chaos. Among the observed routes to chaos, besides the more common period doubling, a new route called loss of frequency locking occurs when the driving frequency is adjacent to a natural oscillation mode. The feedback bandwidth controls the nonlinear dynamics of the system, particularly the number of natural oscillation modes. A computational model has been developed to simulate the experiments and reasonably good agreement is obtained between them. Experiments are described that demonstrate the feasibility of chaotic communications using two TWTs, where one is operated as a driven chaotic oscillator and the other as a time-delayed, open-loop amplifier.