Analysis of Helix Slow Wave Structure for High Efficiency Space TWT
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Analysis of Helix Slow Wave Structure for High Efficiency Space TWT Mukesh Kumar Alaria & A. Bera & A. K. Sinha & V. Srivastava
Received: 12 October 2007 / Accepted: 25 November 2008 / Published online: 6 December 2008 # Springer Science + Business Media, LLC 2008
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. Keywords Dispersion . Interaction impedance . Helix slow-wave structure (SWS) . Traveling wave tube (TWT) . Tip loss
1 Introduction Space TWT is ultra-High vacuum microwave device that is used as high power microwave amplifier in communication satellites [1]. Broad bandwidth, high gain, high efficiency and high linearity of a space TWT desirable for handling a large number of downlink signals in satellite communication. The main components of a TWT are electron gun, helix slow wave structure, Input and output coupler and collector. The helix slow wave structure was designed in 2-section with input and output couplers and tip loss at sever ends using Ansoft HFSS, MWS-CST codes, and CEERI developed M. K. Alaria (*) : A. Bera : A. K. Sinha : V. Srivastava Microwave Tubes Area, Central Electronics Engineering Research Institute, Pilani-333031, India e-mail: [email protected] V. Srivastava e-mail: [email protected]
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J Infrared Milli Terahz Waves (2009) 30:211–216
SUNRAY codes for large-signal analysis of helix TWTs. Dimensions of helix SWS (helix pitch, helix radius ‘a’, tape size) with APBN support rods and IPP barrel assembly were optimized for phase velocity at mid frequency 11.3 GHz synchronous to the electron beam 6.0 kV/100mA. The RF performance of a medium power space TWT is decided by the design of the helix slow wave structure. In this paper the helix SWS has been simulated with tip loss in their real situations of helix TWT as shown in Fig. 1. The helix slow wave structure should allow propagation of the rf wave with desired phase velocity, minimum rf loss and maximum possible rf field across the electron beam (high interaction impedance). The helix SWS is the main deciding factor of the rf performance of a TWT, e.g., power, gain, efficiency, operating bandwidth and
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