Equivalent Circuit Analysis of Serpentine Folded-waveguide Slow-wave Structures for Millimeter-wave Traveling-wave Tubes
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Equivalent Circuit Analysis of Serpentine Folded-waveguide Slow-wave Structures for Millimeter-wave Traveling-wave Tubes M. Sumathy & K. J. Vinoy & S. K. Datta
Received: 27 June 2008 / Accepted: 26 September 2008 / Published online: 1 November 2008 # Springer Science + Business Media, LLC 2008
Abstract A simple equivalent circuit model for the analysis of dispersion and interaction impedance characteristics of serpentine folded-waveguide slow-wave structure was developed by considering the straight and curved portions of structure supporting the dominant TE10-mode of the rectangular waveguide. Expressions for the lumped capacitance and inductance per period of the slow-wave structure were derived in terms of the physical dimensions of the structure, incorporating the effects of the beam-hole in the lumped parameters. The lumped parameters were subsequently interpreted for obtaining the dispersion and interaction impedance characteristics of the structure. The analysis was simple yet accurate in predicting the dispersion and interaction impedance behaviour at millimeter-wave frequencies. The analysis was benchmarked against measurement as well as with 3D electromagnetic modeling using MAFIA for two typical slow-wave structures (one at the Ka-band and the other at the W-band) and close agreement observed. Keywords Equivalent circuit analysis . Serpentine folded-waveguide (SFW) . Slow-wave structure (SWS) . Traveling-wave tube (TWT) Abbreviations SFW Serpentine Folded-waveguide SWS Slow-wave structure TWT Traveling-wave tube
M. Sumathy (*) : S. K. Datta Microwave Tube Research and Development Centre, Bharat Electronics Complex, Jalahalli Post, Bangalore 560013, India e-mail: [email protected] K. J. Vinoy Department of Electronics & Communication Engineering, Indian Institute of Science, Bangalore 560054, India
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J Infrared Milli Terahz Waves (2009) 30:151–158
1 Introduction The serpentine folded-waveguide traveling-wave tubes (TWTs) find applications at millimeter-wave frequencies due to its robust construction, high power capability, simpler coupling and reasonably wide bandwidth. Such a TWT uses a serpentine folded-waveguide slow-wave structure (Fig. 1) that belongs to the fundamentally backward class of circuits like that of a coupled-cavity slow-wave structure. The folded-waveguide slow-wave structure is preferred for millimeter-wave applications for the ease of mechanical fabrication due to its simple structural configuration. A renewed interest is observed for this class of slow-wave structure [1–5] for millimeterwave sources, where the design of the slow-wave structure has been carried out mainly through 3D electromagnetic modeling. However, analytical approaches, for the analysis of dispersion and interaction impedance characteristics of a serpentine folded-waveguide slow-wave structure, have been sparse in the published domain of literature. Only four approaches have been in vogue in this regard: the approaches from S. Liu [6], Na et al. [7], Han et al. [8] and Booske et al. [9]. Liu [6] proposed a si
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