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ABSTRACT: This paper describes the design of tip loss profile on support rod for a high gain, high efficiency helix TWT. The tip loss
profile at sever ends for the input and the output section of the helix slow wave structure has been designed for return loss
at severs ends better than -20dB. The experimental results have been carried out in the input and the output section of the
helix assemblies for the high gain helix TWT to find the return loss in the region of carbon coated tip loss on the support
rods. The experimental result has been compared with the simulated performance for the return loss at the sever ends. The
design of tip loss profile on the support rod for helix TWT has been carried out in real situation using Ansoft HFSS. A good
agreement has been found in the simulated and experimental results.
Journal of infrared, millimeter and terahertz waves 04/2012; 30(7):651-656. · 0.74 Impact Factor
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ABSTRACT: To extract rf power from a traveling wave tube (TWT), proper impedance transformation of the helix slow-wave structure (SWS) has to be done through coaxial couplers to a standard 50 ohm connector. Mismatch of impedance gives poor return loss (RL) behavior and leads to reflection of rf power causing oscillation and destruction of the TWT. In this paper authors have presented design of a co-axial coupler for high power space TWT using CST Microwave Studio and ANSOFT HFSS.
Vacuum Electronics Conference (IVEC), 2011 IEEE International; 03/2011
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ABSTRACT: A helix slow-wave structure (SWS) for a high-efficiency (electronic efficiency >; 25%) Ku-band 140-W space traveling-wave tube (TWT) has been designed. The cold circuit parameters of helix SWS, like propagation constant and on-axis interaction impedance, were determined using 3-D electromagnetic field simulators ANSOFT-HFSS and CST-MWS, and those were validated with the experimental results. The in-house developed large-signal code SUNRAY-1D was used to design a complete helix SWS in two sections with sever and taper to achieve desired output power, gain, efficiency, and other linearity parameters like phase shift, AM/PM factor, and I/M components. The simulated RF performance of the Ku-band 140-W helix TWT was validated with the experimental results. A close agreement between the simulated and experimental results has been found.
IEEE Transactions on Plasma Science 02/2011; · 1.17 Impact Factor
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ABSTRACT: This paper describes the analysis of helix slow-wave structure (SWS) for a high efficiency space traveling wave tube that
is carried out using Ansoft HFSS and CST microwave studio, which is a 3D electromagnetic field simulators. Two approaches
of simulating the dispersion and impedance characteristics of the helix slow wave structure have been discussed and compared
with measured results. The dispersion characteristic gives the information about axial propagation constant (Beta). Which
in turn yields the phase velocity at a particular frequency. The dispersion and impedance characteristics can be used in finding
the pertinent design parameters of the helix slow-wave structure. Therefore a new trend has been initiated at CEERI to use
Ansoft HFSS code to analysis of the helix slow wave structure in its real environment. The analysis of the helix SWS for Ku-band
140W space TWT has been carried out and compared with experimental results, and found is close agreement.
Journal of infrared, millimeter and terahertz waves 02/2009; 30(3):211-216. · 0.74 Impact Factor
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ABSTRACT: Efficiency of Space-TWT is of prime concern along with the long life and high reliability. The collector efficiency plays a major role in determining the desired overall tube efficiency. Various collector efficiency enhancement techniques are employed. This paper describes the use and development of technology of carbon coated OFHC copper electrodes in multi-stage depressed collector for the enhancement of collector efficiency in helix space TWT.
Recent Advances in Microwave Theory and Applications, 2008. MICROWAVE 2008. International Conference on; 12/2008
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ABSTRACT: The main objective of the paper is to make an efficient design of the input and output coaxial coupler for a helix TWTs. An
approach has been developed for the efficient design and analysis of the coaxial couplers in the practical situation. Normally
multi-section impedance transformer approach is used for any wide band coupler. For a space helix TWT, coupler should be wide
bandwidth and small size. In this case coupler is matched with helix slow wave structure and the standard 50-ohm connectors.
The simulated return loss (dB) profile for different type of couplers is obtained by using Ansoft HFSS, CST microwave studio
and compares those with experimental results. The tip loss design at sever ends for the input and the output section has been
also optimized.
International Journal of Infrared and Millimeter Waves 11/2008; 29(12):1083-1090. · 0.58 Impact Factor
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ABSTRACT: 4-stage graphite collector assembly has been designed and developed for a 140W Ku-band space TWT to achieve the collector efficiency more than 80%. The UHV compatible, high density, copper impregnated POCO graphite (DFP-1C) was used to fabricate the four collector electrodes of the 4-stage depressed collector. Copper impregnated graphite material is used for the collector electrodes because of its low secondary electron emission coefficient, high thermal and electrical conductivities, easy machining and brazing, low thermal expansion coefficient and low weight. The graphite material was characterized for the UHV compatibility. The collector electrodes were precisely fabricated by careful machining, and technology was developed for brazing of graphite electrodes with high voltage alumina insulators. Complete TWT with four-stage graphite collector was developed and 140W output power at gain more than 55 dB was achieved. The TWT was pumped from both the gun and the collector ends.
Journal of Physics Conference Series 05/2008; 114(1):012051.
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ABSTRACT: SUNRAY-1D code for large signal analysis of a helix TWT was developed. Effect of circuit loss, sever loss, backward and reflection waves are considered in this model. Higher order harmonics, spurious signals and intermodulation components are also considered in this model. This is fast and it takes less than one minute to find out saturation drive on a P-IV computer. It is also validated with experimental results of several helix TWTs. Agreement for saturated power is achieved within 0.5 dB and for saturated gain within 3 dB.
Vacuum Electronics Conference, 2008. IVEC 2008. IEEE International; 05/2008
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A.R. Choudhury,
R.K. Sharma,
A. Bera,
S.M. Sharma, V. Srivastava,
P.V. Bhaskar,
R.R. Singh,
K.S. Prasad,
S. Ghosh,
V. Kiran,
R.R. Patnaik
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ABSTRACT: A Ku-band 140 W space TWT of gain (>55 dB), electronic efficiency (>24%), collector efficiency (>75%), overall efficiency (>55%), I/M components (<-12 dBc) for frequency 10.9-11.7 GHz has been designed and developed for satellite communication system. This paper presents critical design issues and approach related to different assemblies like electron gun, PPM focusing, helix SWS, input & output couplers, and 4-stage depressed collector in order to meet the stringent requirement of space TWTs.
Vacuum Electronics Conference, 2008. IVEC 2008. IEEE International; 05/2008
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ABSTRACT: In self-organizing networks, nodes are expected to perform services (such as forwarding packets) for one another. The design of incentive mechanisms that lead nodes to cooperate towards a network-wide goal is crucial for the deployment of such networks in commercial environments. In this paper we employ game theory to analyze a behavior-based incentive scheme for node cooperation in packet forwarding. Our analysis includes an evaluation of the effectiveness of the scheme in achieving an optimal solution, as well as stability considerations. One of the contributions of this work is the modeling of imperfect monitoring, recognizing that in practice nodes do not have perfect information regarding their neighbors' actions on which to base their decisions of whether to cooperate.
Communications, 2006. ICC '06. IEEE International Conference on; 07/2006
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ABSTRACT: All reflections present in the device may cause oscillations and hence instability in a high efficiency traveling wave tube (TWT) amplifier. In a helix TWT, a coating of lossy material is deposited on the helix support rods to absorb these reflections. Carbon is a very commonly used material for this type of coating, and may be deposited by a number of techniques. But other materials may also be employed for this purpose. In the present work, coatings of carbon, nickel and iron have been made and evaluated for their attenuation performance at microwave frequencies. Three APBN rods have been coated with carbon in different thicknesses by a pyrolytic deposition method, while two rods of alumina have been coated with an electro-deposition method. An experimental set-up involving a narrow-height wave-guide with a hole was used to measure the attenuation of the coated rods at 6.0 GHz. Very significant results have been obtained in the experimental study and it is concluded that carbon coated rods have maximum attenuation but nickel and iron can be used also for attenuator purposes.
Microwave and Telecommunication Technology, 2004. CriMico 2004. 2004 14th International Crimean Conference on; 10/2004
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ABSTRACT: High efficiency space travelling wave tubes (TWT) are essentially required for defense coherent radars and for satellite communication systems as a high power, high gain microwave amplifier. High efficiency (more than 60%) and high linearity (phase shift less than 30°) are very important aspects of a space TWT. Since 1997, efforts have been made at CEERI (jointly with BEL, Bangalore) for the successful design and development of high efficiency TWTs for space applications. Two projects have been sponsored by ISRO, Bangalore. A C-band 60 W space TWT has been successfully designed and prototypes have been developed jointly with BEL. Desired RF and electrical specifications were achieved over an extended frequency range of 3.40 GHz to 4.20 GHz with an output power more than 60 W, large-signal gain more than 50 dB, overall efficiency more than 55%, AM/PM factor less than 4 degrees/dB, and harmonic components and intermodulation (I/M) components more than 12 dBc down. Agreements between the simulated and the experimental values of the AM/PM factor, I/M components and the second harmonic power were achieved well within 10%. 'Quality assurance' (QA) of the C-band 60 W TWT has been initiated for space qualification. The design of a radiation-cooled Ku-band 140 W space TWT has recently been completed and the design has been transferred to BEL for further joint development.
Microwave and Telecommunication Technology, 2004. CriMico 2004. 2004 14th International Crimean Conference on; 10/2004
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ABSTRACT: Summary form only given. The synthesis and analysis of a Pierce-type electron gun has been developed from first principles to design the gun of a C-band, 60 W (CW) space TWT. The design of the gun includes an ion barrier anode A<sub>0</sub>, kept at a positive potential with respect to the ground anode A<sub>1</sub>, to prevent ions from flowing towards the cathode and to reduce ion bombardment at the cathode and hence enhance the life and reliability of the gun. Encouragingly, the space TWT actually developed that incorporates the electron gun designed by the authors has met all the desired specifications.
Vacuum Electronics Conference, 2004. IVEC 2004. Fifth IEEE International; 05/2004
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ABSTRACT: An approach for designing an electron gun for a high efficiency, high linearity space traveling wave tube (TWT), has been presented. A low convergent (<10 : 1) Pierce electron gun of beam perveance 0.43 μP has been designed for a high gain, high linearity and high efficiency C-band 60 W Space TWT using in-house developed two-dimensional FDM based gun and collector simulation code PIERCE. In this gun, the first anode (isolated from the ground anode) has been kept nearly 100 V above the ground anode to act as an ion barrier for increasing cathode life and to regulate beam current over the lifetime of the tube. An M-type dispenser cathode of diameter 3.20 mm has been used for cathode loading of less than 1.0 A/cm2 and heater wattage around 3.0 W. The magnetic focusing with integral-pole-piece barrel assembly and periodic-permanent magnets (PPM) have been designed using in house developed two-dimensional FDM based code SUNMAG. The practical problem of linking requisite cathode flux to the cathode for confined flow of the electron beam with low convergence factor has been sorted out by gradually increasing the PPM magnetic field. The magnetic field has been increased in steps from the gun and over the first five magnets varying from Brillouin field (B B) value to twice B B for achieving the electron beam with scalloping less than 10%. Agreements between the simulated results and the experimental results for the beam current and magnetic field profile have been achieved within 8%. The dynamic beam transmission (under rf operation of the tube) has been achieved better than 98% in the tube.
International Journal of Electronics. 02/2004; 91(2):97-105.
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ABSTRACT: In this paper helix SWS (slow wave structures) for Ku-band space TWT is presented to achieve RF output power 140 W with gain more than 50 dB over the frequency band 10.9 to 11.7 GHz with the optimum values of efficiency, linearity, stability, weight and size. The criteria of selecting both beam and circuit parameters are discussed. The simulated RF performance for space TWT are shown.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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ABSTRACT: In this paper, the development of a high efficiency TWT for space applications has been presented. The tube has been developed for 60 watt output power in C-band with TWT efficiency 50%. The electron gun developed for the tube is Pierce convergent type electron gun with an ion barrier. The important aspect of this tube is the development of a four stage depressed collector. The depression of the collector electrodes are so adjusted to achieve collector efficiency in excess of 70%.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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ABSTRACT: Two-dimensional package EGUN was used for the simulation of multistage collector. Based on this package a pre- and a post-processor have been developed which make the package user friendly and analyses the performance of the collector. In this article, we modelled the multistage collector for high efficiency space TWT.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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ABSTRACT: An electron gun with dual anodes has been designed for a Ku-band 140 W space TWT. The initial gun geometry based on the design parameters such as beam voltage (5.8 V), beam current (90 mA), waist radius (0.34 mA) and emission current density (1.0 A/cm<sup>2</sup>) has been synthesized. The gun geometry is worked out with beam forming electrode (BFE) and anodes. The gun geometry has been optimized using Hermannsfeldt's gun simulation code E-GUN for the desired beam flow and beam current. A comparison between synthesis and simulated results for the electron gun has been analysed.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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ABSTRACT: Input and output couplers have been designed for Ku-band 140 W TWT with minimum reflection and transmission loss over the desired frequency range of 10.9 to 11.7 GHz. The software package Ansoft HFSS version 8.5 was used to simulate the coupler terminated with the actual helix slow wave structure (SWS). The SWS is a tungsten tape helix, which is supported inside the metallic barrel assembly using three rectangular shaped APBN support rods at 120 degrees. The return loss characteristics for both input and output couplers were investigated.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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ABSTRACT: Summary form only given. A four-stage axisymmetric depressed collector was successfully designed and developed to recover nearly 80% of the spent beam kinetic energy for a high efficiency C-band 60 W space TWT. The PIERCE program [LK-MTRDC] was used to optimize shape, size and operating depressed voltage of each electrode of the 4-stage depressed collector for achieving optimum energy recovery from the spent electron beam with minimum loss of collector efficiency caused by secondary electrons from back streaming. The program uses geometrical parameters of the electrodes and the spent beam trajectories data. The electron beam trajectories data were generated from the SUNRAY-3D large-signal model [VS-CEERI] and SUNBRS program [VS-CEERI] for the TWT operating at saturation output power at centre frequency 3.90 GHz. The SUNBRS code was used for analyzing the spent beam passing through the beam refocusing section (BRS) which was used before the collector for improving its performance. Radial velocities in the spent beam were reduced by decreasing PPM focusing magnetic field along the BRS.
Vacuum Electronics Conference, 2002. IVEC 2002. Third IEEE International; 02/2002
