P. Raja Ramana Rao

Optimization of couplers of TWT using TDR method

This paper describes usefulness of time-domain method (TDR) for optimization of couplers of TWT. Initially the method is used for a coaxial transmission line having four sections. Due to the transitions between the sections there exist some reflections. By knowing exact position of reflections one can optimize for better VSWR by introducing compensating steps. This method has been extended for the optimization of output coupler of a TWT by estimating the positions of discontinuities and optimizing the design for better VSWR. This method can be extended for any type of couplers like waveguide-to-coaxial transitions, or any other microwave transmission lines.

Experimental verification of the performance of a depressed collector for a linear beam tube

This paper describes the simulation of a single stage depressed collector using PIERCE and CST Studio including secondary electron emission effects. This collector was developed and integrated with a linear beam tube. The experimental efficiency of the collector agrees well with the simulated efficiency of the collector. The thermal analysis of the collector also has been carried out using ANSYS and agrees well with the measurements.

P2-3: Exploration of a broadband ‘semi-vane’ helical SWS

Slow-wave characteristics of a broadband ‘semi-vane’ helical SWS have been studied using 3D electromagnetic modeling in CST-studio. The geometry has shown promises for better broadbanding potential compared to a conventional segment loaded configuration. Also, the results have shown that placement of segments closer to the support rods provides a better negative dispersion.

Effect of inhomogeneous dispersion shaping of a helical SWS on the backward-wave oscillation criterion

The effect of inhomogeneous dispersion shaping of a helical SWS on the backward-wave has been studied. Theoretical simulations of three types of dispersion, namely, positive, flat and negative, achieved in an inhomogeneous structure and the interaction impedance characteristics thereof were carried out. The analysis of backward-wave oscillation criterion has been carried out to assess the effects of dispersion shaping and the beam-filling factor. A negative dispersion structure has been found to be advantageous in improving the threshold for backward wave oscillation.

Measurement of dispersion and azimuthal interaction impedance of vane-loaded coaxial wave guiding structures

Vane-loaded coaxial structures have been analyzed for dispersion and interaction impedance [1–2]. However the measurement of these parameters has not been reported. A method of simulated measurements was reported [3], in which the dispersion and azimuthal interaction impedance were obtained by using 3D-simulation software as a tool for conducting simulated experiment. In the present paper the results obtained by actual measurements are compared with simulation results obtained using CST-Micro-wave studio.

Simulation of collectors for TWT including the effects of SEE using PIERCE

This paper describes the simulations of a single-stage depressed collector and a 3-stage depressed collector including the effects of secondary electron emission (SEE) using a 2D FDM based code PIERCE and compares the single-stage collector efficiency against experimental results at different frequencies.

Simulation of a collector for a gyro-device using PIERCE

Simulation of an axis-symmetric depressed collector for a gyrating hollow electron beam is presented in this paper. The simulation including the effects of the magnetic field and secondary electrons has been carried out using a 2D FDM based code PIERCE (Program for Improved Electron Ray-tracing in Collectors and Electron guns). Further, effects of magnetic field profiling and its advantages in thermal management are also demonstrated.

Equivalent circuit analysis of a plasma-filled helix slow-wave structure

An equivalent circuit analysis of a plasma-filled helical slow-wave structure immersed in a strong longitudinal magnetic field was developed to analyze the dispersion characteristics of the structure. The analysis predicted the formation of hybrid-plasma slow waves in the structure and the enhancement of longitudinal electric field inside the helix for facilitating strong beam-wave interaction in a device like a plasma-filled traveling-wave tube.

P3-20: Analysis of dispersion and interaction impedance for vane-loaded coaxial waveguide structure

Vane loaded coaxial structures have been found useful for mode rarefaction, when used in oversized, over-moded gyrotron amplifiers. Also such circuits can compensate for the gain reduction which normally occurs while broad-banding of gyro-TWTs. This magnetron like structure was analyzed for its cut-off wave numbers by various techniques. In the present paper the dispersion and interaction impedance characteristics are obtained by boundary matching technique [1]. The results are compared with simulated data obtained using CST microwave studio for TE01-mode.

Characterization of vane-loaded cylindrical wave guiding structure using NRP technique by simulated experiment

There is a lot of interest in vane-loaded cylindrical wave-guiding structures for fast-wave devices. Dispersion and interaction impedance are the two basic characteristics defining the structures for their relative merits and demerits for an intended application. A mm-wave vane loaded structure is evaluated for these parameters by using a non-resonant perturbation (NRP) technique. The results are compared with the results obtained from analysis and simulation.