Asian Journal of Physics Vol 32, Nos 9 – 12 (2023) 453-461

A simple and fast split-model optimization technique for RF couplers of helix traveling-wave tubes

Raktim Guha1,2 and Sanjay Kumar Ghosh1,2
1Academy of Scientific and Innovative Research (AcSIR), CSIR-HRDG, Ghaziabad- 201 002, India
2Vaccum Electron Devices Group, CSIR-CEERI, Pilani-333 031, India
Dedicated to Prof B N Basu

A simple and fast split-model technique based on analysis and simulation was developed for the optimization of the RF coupling system of a helix traveling-wave tube (TWT). The proposed technique addresses the tedious design of RF power coupling to a non-uniform helix pitch section of the slow-wave structure of the TWT that becomes all the more tedious if one uses an H-plane end-launcher transition rather than an E-plane launcher, such as, probe or door-knob type of transition to reduce the size of the coupling system with better S-parameters. This proposed split-model optimization technique significantly reduced the optimization time by > 95% as compared to the conventional optimization technique without sacrificing the desired accuracy in the value of voltage standing wave ratio (VSWR). The proposed technique yielded the value of VSWR close to that predicted by the conventional optimization technique. © Anita Publications. All rights reserved.
Keywords: Coaxial couplers, Rectangular waveguide transition, Impedance matching, Helix slow-wave structure (SWS), Traveling wave tube (TWT).

Peer Review Information
Method: Single- anonymous; Screened for Plagiarism? Yes
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  1. Jia B, Baik C.-W, Park G.-S, The design of the input and output transformer for wideband helix TWT, in Proc 2nd International Conference on Microwave and Millimeter Wave Technology, Beijing, China, September 2000,, (2000)715–719, doi: 10.1109/ICMMT.2000.895787.
  2. Sinha A K, Singh V V P, Srivastava V, Joshi S N, On the design of coaxial coupler having multi-section short transformer for compact sized power helix traveling wave tubes, in Proc Int Vac Electron Conf, (2000),p2.25–p 2.26; doi: 10.1109/OVE:EC.2000.847499.
  3. Agarwal A K, Raina S, Kumar L, A novel approach for simulation of coaxial coupler for helix TWTs using HFSS, in Proc 4th IEEE Int Vacuum Electron Conf, (2001)58–59; doi: 10.1109/IVEC.2011.5746942.
  4. Duffield M J, A technique for designing the RF connectors used on Helix TWTs, in Proc IEEE Int Vac Electron Conf (IVEC), (2007)1–2; doi: 10.1109/IVELEC.2007.4283389.
  5. Ghosh T K, Carter R G, Challis A J, Rushbrook K G, Bowler D, Optimization of Coaxial Couplers, IEEE Trans Electron Devices, 54(2007)1753–1769.
  6. Rao K V, Naidu V B, Rao P R R, Datta S K, Simulation of RF coupler of a multi-section TWT with matched sever-loss,” 2009 IEEE International Vacuum Electronics Conference, (2009)455-456, doi: 10.1109/IVELEC.2009.5193567.
  7. Rao P R R, Datta S K, Kumar L, Optimization of Couplers of TWT using TDR Method, in Proc IEEE Int Vac Electron Conf (IVEC), (2012)79–80; doi: 10.1109/IVEC.2012.6262082.
  8. Jain P K, Basu B N, Electromagnetic wave propagation through helical structures, in Electromagnetic Fields in Unconventional Materials, (Eds) Singh O N, Lakhtakia A, (Hoboken, NJ, USA: Wiley), 2000.
  9. CST AG, Darmstadt, Germany. CST STUDIO SUITE. Accessed: 2018. [Online]. Available:
  10. HFSS V18.0: Ansoft Corporation.
  11. Naidu V B, Datta S K, Rao P R R, Agrawal A K, Reddy S U, Kumar L, Basu B N, Three-Dimensional Electromagnetic Analysis of Attenuator-Coated Helix Support Rods of a Traveling-Wave Tube, IEEE Trans Electron Devices, 56(2009)945–950.
  12. Rizzi P A, Microwave Engineering: Passive Circuits. New Delhi: Prentice Hall International, 1988.
  13. Li Q, Y. Zhang, L. Qu, Y. Fan, Quasi-Static Analysis of Multilayer Dielectrics Filled Coaxial Line Using Conformal Mapping Method, in Proc IEEE International Conference on Computational Electromagnetics (ICCEM), (2018)1–3, doi: 10.1109/COMPEM.2018.8496545.
  14. Yang D.-Y, Design and Fabrication of an End-Launched Rectangular Waveguide Adapter Fed by a Coaxial Loop, J Inf Commun Converg Eng, 10(2012)103–107.
  15. Gesche R, Löchel N, Two Cylindrical Obstacles in a Rectangular Waveguide- Resonances and Filter Applications, IEEE Trans Microw Theory Tech, 37(1989)962–968.
  16. Pandharipande V M, Das B N, Equivalent network of a variable-height post in a rectangular waveguide, Proc Inst Electr Eng, 124(1977)1160–1162.