Sascha Meyne

Hot matching conditions of coupled-cavity traveling-wave tubes

An analysis of the propagation characteristics of coupled-cavity (CC) delay lines in traveling-wave tubes (TWTs) under hot conditions is proposed. Using this approach a necessary impedance level at the end of the periodic line is derived that leads to minimum input reflections during operation. From this matching condition a required cold input reflection can be predicted which is in general different from the one commonly used.

Taper optimization for helix traveling-wave tubes using adaptive simulated annealing

A specialized version of adaptive simulated annealing is presented. It is designed to optimize helix tapers for traveling-wave tubes in terms of output power and linearity based on the saturated tube characteristics. The algorithm is tested on a Ku-band traveling-wave tube and the results are presented.

Improved gain estimation for folded-waveguide traveling-wave tubes using Madey's Theorem

A small-signal model for the gain estimation of traveling-wave tubes with folded-waveguide delay lines is derived from perturbation theory. The model extends an existing formulation from literature, and increases its accuracy significantly. The results are compared to full-wave particle-in-cell simulation.

Design, fabrication, and measurement of nose-cone loaded folded-waveguide delay line in Q-band

A Q-band folded-waveguide delay line is presented which is loaded with nose cones that are intended to increase the beam-wave coupling in a traveling-wave tube. The fabrication process is briefly outlined and one-port measurement results are evaluated to compare the dispersion with full-wave results. The results prove the concept of field enhancement due to the nose cones with an acceptable increase in manufacturing complexity.

Nose-cone loaded folded-waveguide delay lines for Q-band traveling-wave tubes

A modified folded-waveguide (FW) delay line for traveling-wave tubes (TWTs) is proposed. The amplifier performance is assessed by full-wave and interaction simulation. Properly designed nose cones are shown to enhance the beam-wave coupling. This, in turn, improves the amplifier gain, a weak point of conventional FW-TWTs. The achievable beam efficiency is increased without sacrificing too much bandwidth.

Design procedure for hot-matched severs in folded-waveguide traveling-wave tubes

A design procedure for a hot-matched sever for folded-waveguide traveling-wave tubes (FW-TWTs) is proposed. To determine a starting point for a suitable load design, a realistic three-dimensional sever structure is developed using equivalent circuits and subsequent particle-free (cold) full-wave simulation. Additional wave impedance information, obtained by a small-signal eigenvalue analysis, is used to improve the termination for hot operation. The final full-wave optimization is then performed in the presence of the electron beam with only moderate computational effort. This procedure is applied to develop a sever structure for a given frequency point at Q-band. The simulated results support the approach.

Large-Signal 2.5-D Steady-State Beam-Wave Interaction Simulation of Folded-Waveguide Traveling-Wave Tubes

A large-signal beam-wave interaction code for folded-waveguide traveling-wave tubes is presented. Formulation in frequency domain yields fast results of the steady state. The slow-wave structure is described by an equivalent circuit, while the electrons of the beam are modeled by means of a particle-in-cell approach. The latter exploits the periodicity of the electromagnetic fields in the beam tunnel region, thus allowing to work with a relatively low number of injected particles compared to conventional implementations. Physically consistent solutions are then obtained iteratively by incorporating the well-established Broydens method. Further improvement in terms of computation time is achieved by initializing the iterative algorithm with results from previous simulations. The approach is verified by a comparison with published interaction simulation results. Single-frequency responses are obtained within a few minutes, which compares favorably with other specialized simulation packages and enables device optimization with acceptable effort.

Q-band high-power traveling-wave tube with optimized folded-waveguide delay line

A folded-waveguide delay line is proposed for traveling-wave tubes. It is intended for satellite communications at Q-band, thus aiming for high output power and efficiency. The delay line is optimized using Adaptive Simulated Annealing, and interaction is simulated using a large-signal tool.

Large-Signal Investigation of Cold and Hot Matched Coupled-Cavity Traveling-Wave Tubes

Abstract The implications of different matching conditions for coupled-cavity traveling-wave tubes are considered. Using a small-signal approach the characteristic impedance for the coupled (hot) beam-wave system is derived. It is taken as reference impedance to model ideal transformers and severs. This matching condition is compared to the standard cold match and both cases are analyzed using a large-signal interaction tool. The implications on input reflection and output gain are discussed.

Waveguide-Based Optical Phased Array

A concept for a 3-D waveguide system, which can be used for optical phased arrays, is presented in this letter. We implemented static phased arrays with rod waveguides of different widths, which can be used for holographic applications. They are fabricated with direct laser writing, a technique based on two photon polymerization. As the element size of our phased array can be in the order of the visible wavelength, relatively large diffraction angles of up to 40° can be reached.