A Simple and Accurate Analysis of Conductivity Loss in Millimeter-Wave Helical Slow-Wave Structures |
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Authors: | S K Datta Lalit Kumar B N Basu |
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Affiliation: | (1) Microwave Tube Research and Development Centre, Defence Research and Development Organization, Bharat Electronics Complex, Jalahalli Post, Bangalore, 560013, India;(2) College of Engineering and Technology, Lodhipur, Rajput Road, Moradabad, 244001, India |
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Abstract: | Electromagnetic field analysis of a helix slow-wave structure was carried out and a closed form expression was derived for
the inductance per unit length of the transmission-line equivalent circuit of the structure, taking into account the actual
helix tape dimensions and surface current on the helix over the actual metallic area of the tape. The expression of the inductance
per unit length, thus obtained, was used for estimating the increment in the inductance per unit length caused due to penetration
of the magnetic flux into the conducting surfaces following Wheeler’s incremental inductance rule, which was subsequently
interpreted for the attenuation constant of the propagating structure. The analysis was computationally simple and accurate,
and accrues the accuracy of 3D electromagnetic analysis by allowing the use of dispersion characteristics obtainable from
any standard electromagnetic modeling. The approach was benchmarked against measurement for two practical structures, and
excellent agreement was observed. The analysis was subsequently applied to demonstrate the effects of conductivity on the
attenuation constant of a typical broadband millimeter-wave helical slow-wave structure with respect to helix materials and
copper plating on the helix, surface finish of the helix, dielectric loading effect and effect of high temperature operation
– a comparative study of various such aspects are covered. |
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Keywords: | Conductivity loss Circuit loss Circuit attenuation Helix slow-wave structure (SWS) Helix traveling-wave tube (TWT) Wheeler’ s incremental inductance rule |
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