Tushar K. Ghosh

Design of Helix Pitch Profile for Broadband Traveling-Wave Tubes

To improve the performance of a broadband traveling-wave tube (TWT), a helix pitch profile incorporating a section with reduced phase velocity followed by a positive phase-velocity taper is used. A simple technique to design a pitch profile of this kind is elaborated upon and later applied to an existing 6-18-GHz uniform pitch mini-TWT to improve its interaction efficiency. By using the newly designed helix, a TWT is developed, which shows increases in electronic efficiency and output power up to 8.75% points and 2.6 dB (75 W), respectively. Further application of this method to another uniform pitch baseline tube results in similar improvements.

Optimization of Multistage Depressed Collectors

Random walk and genetic algorithm techniques have been implemented in a 3-D collector simulation code to automate the design optimization of multistage depressed collectors. An axisymmetric four-stage collector and an asymmetric two-stage collector have been optimized following both approaches. Procedures for the implementation of these methods in any suitable code and simulated performance of the collectors are demonstrated. The results show significant improvement in the collector performances due to optimization. A comparison between the optimum collector performances that were obtained using these methods has also been carried out.

Optimization of Coaxial Couplers

A simple and accurate method has been developed to optimize the performance of coaxial couplers for traveling-wave tubes using a 3-D electromagnetic field simulation code. The new technique, which is a combination of numerical and analytical procedures, is presented with a comparison with conventional practice. By using this method, a number of couplers with Sub- Miniature A, Threaded Neill-Concelman, and waveguide output for different tubes were modeled, validated by the experimental cold test data, and optimized. The use of this technique can reduce the optimization time by up to 90% in comparison with the conventional numerical only approach.

Improvements in Performance of Broadband Helix Traveling-Wave Tubes

The effectiveness of positive phase velocity tapering to improve the performance of a broadband helix traveling-wave tube (TWT) has been investigated. A large-signal model of an existing 4.5-18 GHz two-section mini-TWT with uniform pitch has been validated against the experimental results, and used as a starting point to design and develop a number of TWTs with different taper lengths. Comparisons between the experimental results of uniform pitch TWT and positively tapered TWTs show significant improvements in output power, electronic efficiency, and second harmonic content throughout the operating frequency band for the positively tapered TWTs. Increases in electronic efficiency and output power up to 5.2% points and 50 W (1.7 dB), respectively, have been achieved.

Improvements in Broadband Performance of Mini-TWTs at e2v technologies

Positive phase velocity tapering has been implemented to improve the broadband performance of helix traveling wave tubes (TWTs). The slow wave structures of a mini-TWT and a midi-TWT have been optimized using this technique. A comparison between the actual performances of the tubes with uniform and positive tapered pitch shows a significant improvement in efficiency and power at the higher end of the frequency band of operation in the later case.

An improved magnetic field simulator - MAGFLD

An improved two-dimensional simulator MAGFLD has been developed which is useful for the design and simulation of periodic permanent magnet (PPM) focusing system for linear beam tubes. At present, input is possible only through the input file, which is very simple and user friendly. A complete PPM circuit is generated using the coordinates of first pole piece, first magnet, gun adapter (if the structure is a-periodic) and the region of computation. Small mesh units of either square or rectangular shapes can be used with mesh refinement capability in one or more regions in any or both directions for better accuracy of the solution. Materials with different magnetic permeability can be modeled by defining a characteristic value for each mesh point of the geometry. The effective potential value at each point in the region of interest is calculated based on the vector potential model by using the 5-point finite difference method and the solution is achieved by over relaxation technique for faster convergence. This package has an interface with EGUN to model the electron gun and collector under the influence of magnetic field. Versatile color graphics are capable of plotting both axial magnetic field and flux lines along with the magnetic circuit. MAGFLD has been validated against some published data and experimental results.

Optimization of helix pitch profile for broadband Mini-TWTs

Broadband helix traveling-wave tubes (TWTs) with a pitch profile incorporating a section of reduced phase velocity followed by a positive taper show significant improvement in output power. A simple technique is described here to optimize such slow-wave structures taking an existing uniform pitch mini-TWT as a baseline tube. A comparison has been made among the actual performances of the TWTs with three different pitch profiles such as, uniform, positive taper and negative step positive taper. It has been observed that the improvement in output power is highest for the last TWT over 6-18 GHz operating band.

Design and Evaluation of Electron Gun and Beam Focusing for Ku-band 140W Space TWT

A low perveance (0.22 muP) electron gun for Ku-band 140W space traveling wave tube (TWT) has been designed, using E-GUN and TRAK codes. Pierce type electron gun with an electrically isolated beam forming electrode (BFE) and an ion barrier anode (A0) has been opted. An M-type dispenser cathode with low cathode

Design optimisation of multistage depressed collectors for high efficiency travelling wave tubes using genetic algorithm

The design of a symmetric and an asymmetric collector has been optimised using the genetic algorithm. The improvement in collector efficiency in both cases is remarkable.

Development of multistage collectors for broadband helix TWTs

This paper describes the design strategies of multistage collectors. Using this technique three different types of collectors with different number of stages have been designed, developed and experimentally evaluated for broadband traveling wave tubes (TWTs). Simulated performance and experimental results of these collectors are presented in detail.