A planar inter-digital type slow-wave structures is proposed for forward first-space-harmonic operation. The proposed structure supports hybrid (even and odd) modes. The analysis of the proposed structures is carried out using CST-Microwave studio for the mode analysis and slow-wave characteristics (dispersion and interaction impedance characteristics) at W-band. Fabrication and cold test measurement of the structure is in progress and the measured results will be presented at the time of conference.

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.

A new class of Multi helix based THz vacuum electron devices is under consideration easily fabricated using unconventional applications of microfabrication technology and modern computer modeling. This configuration will extend the operating range of the helical slow wave circuit into the THz frequency band. The design of a ~140 GHz amplifier is described, which can be extended beyond 1.0 THz.

Analysis of a W-band meander-line slow-wave structure has been carried out using quasi-TEM approach and validated against CST-Microwave studio for the dispersion and interaction impedance characteristics. A waveguide coupler is designed using HFSS and large signal analysis is carried out for output power and gain. A cold test model of the structure is fabricated at Ku-band frequency and cold test measurement is carried out for the dispersion characteristics and results are compared against analysis results.

The vacuum electronic era started with the invention of vacuum diode by JA Fleming in 1904. However, the foundation of microwaves was laid in India much earlier by one of the fathers of radio science Acharya Jagdish Chandra Bose in 1890's in Calcutta. He used waveguides, horn antenna, dielectric lenses, polarizer's and even semiconductor detector, while working at the 2.5 cm to 5 mm wavelength. Today, the vacuum electronic devices (VEDs) are an essential component of many defense, space, and high energy research and civilian systems employing rf, microwaves, or x-rays or simply high speed switching. Defense systems like Radar, electronic warfare, communication and missile systems; high energy particle accelerators, TeV colliders, fusion reactors, industrial and domestic-ovens, medical imaging, hyperthermia, high power electric transmission etc. all require VEDs. Presently, India is one among just a dozen countries in the world having the ecosystem of academia, research laboratories production enterprises and a significant domestic market in defense, space, civilian, high energy research and ISM sectors to nurture innovation in these devices.

This paper describes the design and experimentation of electrostatic focusing of electron beam using a demountable vacuum measurement setup. Initially a focusing setup is designed for focusing a single on-axis low perveance beam. The design was carried out using an in house developed 2.5 D finite difference electron optics code PIERCE and CST Particle Studio. This focusing scheme is being extended for multiple beams of same perveance for a compact klystron device.

Electromagnetic field analysis of a helical slow-wave structure was carried out following tape-helix model incorporating the effects of space-harmonic propagating modes and the effects of finite width of the tape. Using this analysis, RF loss in the structure due to the finite conductivities of the constituent materials was estimated. The analysis was validated against published results for a segment-less structure and against HFSS simulation for a metal segment loaded structure.

In a broadband coupled-cavity slow-wave structure, the problem of bandedge oscillation is overcome by resonant loss technique by introducing lossy dielectric resonators in the cavity. To reduce the dimensions of the dielectric resonators, high lossy and high dielectric constant, materials are used. In this paper, the effects of introducing 2, 4 and 8 lossy dielectric resonators (operating either on E010- or H111-mode), on the dispersion, interaction impedance and start oscillation current are studied.

This paper describes the simulation of an axi-symmetric 2-stage depressed collector including the effects of secondary electrons using a 2D FDM based code and compares its efficacy against experimental results and 3D simulation using CST Particle Studio. The paper also demonstrates the 3D simulation of a tilted electric field (TEF) collector using CST Studio for arresting the secondary electron back-migration.

Small-signal analysis of a plasma-filled helix traveling-wave tube was developed following Eulerian hydrodynamic approach. The electron beam was treated as a moving charged fluid and the plasma a stationary quasi-neutral fluid. The coupled circuit and electronic equation was developed and a Pierce-type hot dispersion relation obtained, which was then interpreted for the gain-frequency response of the device. The analysis was validated against an existing approach that treats the interaction as a boundary value problem by considering the beam-plasma system as a propagating medium of an equivalent relative permittivity tensor.

In this present work, optimization of a Ku-band waveguide coupler for coupled-cavity traveling-wave tube waveguide coupler has been carried out using an Artificial Neural Network (ANN). The ANN model takes the cavity physical dimensions as the input and the VSWR as the output. The training data for the network has been taken from the numerical simulation using the 3D electromagnetic simulation software MAFIA. The ANN uses a 3 layer feed-forward network consisting of 60 neurons for each layer. The ANN was trained so that the simulated error will be less than 10 %.

The waveguide and the coaxial-probe type wideband high power TM0n-mode couplers (n = 1, 2) were designed and qualified with respect to the coupling factor using the wheel-type mode launchers. The mode launchers and the mode couplers were simulated and experimentally tested, the former for the VSWR and the latter for the coupling factor. The coupler chamber has been used in single-shot experiments, the values of the measured frequencies of coupled output of a typical vircator agreed with those predicted values by particle-in-cell code simulation using MAFIA.

In the present paper various class of helix slow wave structures, right from S-band to Ka-band, dielectric loaded and segment loaded have been analyzed to obtain the dispersion and impedance characteristics using MAFIA and tape helix model HELTAPE and the results compared. For the MAFIA simulation ten turns of helix were modeled in the cylindrical coordinate system by varying axial and azimuthal coordinates consistent with the formula of a circular helix.

This paper describes a novel approach to model and analyze a helix to coaxial transition using three-dimensional electromagnetic computer code, the High Frequency Structure Simulator (HFSS) based on the Finite Element Method (FEM). For a K-Ka band helix TWT, RF Coaxial Coupler consisting of a helix to coaxial transition and a RF coaxial window is designed. The novelty of this simulation approach is that the RF matching to helix slow wave structure at the other end was provide by lossy resistive thin films being placed them on either side of three dielectric support rods. For a broadband K-Ka band helix TWT where the optimum VSWR expected for a transition is high, the used approach is promising of giving more realistic estimate of the performance of a transition compared to the method in which at both ends of helix a identical transition is modelled. The simulation approach for the coupler of an X-Ku band production tube compares well with measured results.

Large-signal analysis for backward-wave oscillation (BWO) start condition in a helix travelling-wave tube (TWT) amplifier has been developed. The effects of distributed circuit loss and beam-filling factor on start oscillation condition are investigated, and large-signal analysis results are presented vis-a-vis Eulerian analysis results.

In secondary emission modelling programs, the total secondary emission yield is generally estimated using semi-empirical formulae proposed by Vaughan. The backscattered yield is often estimated simply as a constant fraction of the total yield, which is too simplistic, or by using a polynomial fit to the experimental data. The angular distribution of backscattered electrons on the energy and incident angle using the functional dependence.

A simple scheme of broadbanding a helical slow-wave structure is proposed using helix support structure made of composite chiral dielectric material. The dispersion relation of the slow-wave structure obtained by sheath-helix field analysis and the dispersion behavior of a typical structure analyzed. It was seen that negative dispersion characteristics, required for broadband operation of the device, could be achieved by merely controlling the chirality parameter alone.

A design procedure for an inter-digital slow-wave structure for TWTs is presented using equivalent circuit approach. The results are refined using numerical simulations by modeling the structure using the software package MAFIA. The dimensions of the inter-digital structure are compared with those of a conventional coupled-cavity slow-wave structure designed at the same center frequency. It is concluded that the size and weight of the inter-digital structure is significantly reduced as compared to that of a coupled-cavity structure.