volume | PIER Journals

Abstract

A simple field analysis was developed for helical slow-wave structure symmetrically supported by rectangular shaped discrete dielectric support rods partially embedded in the metal segments projecting radially inward from a metal envelope for wideband traveling-wave tubes. The tape helix model was used for the prediction of the dispersion relation and the interaction impedance characteristics. The closed form simplified expressions are obtained by combining the tape model dispersion relation for free-space helix and the dielectric loading factor obtained for the loaded helix in the sheath model. The dispersion characteristics and the interaction impedance characteristics obtained by the present analysis were compared with other more involved analytical method reported in the literature for the similar helical slow-wave structure and found to be in close agreement. The present analytical results were also validated against HFSS simulation with an agreement within 5% for both the characteristics for a wide range of structure parameters. An appropriate choice of the structure parameters (helix thickness, height of the metal segments, material of the dielectric support rods, wedge segments angle and helix pitch) provided the phase velocity varying with frequency corresponding to flat to negative structure dispersion with an appreciable interaction impedance values over a wide frequency band. The present analysis enjoys simplicity and establishes the potential of theproposed helical interaction structure for its employment in wideband traveling-wave tubes.

1. Ghosh, S., A. K. Sinha, R. K. Gupta, S. N. Joshi, P. K. Jain, and B. N. Basu, "Space-harmonic effects in helical slow-wave structure --- An equivalent circuit analysis," Progress In Electromagnetics Research, Vol. 30, 85-104, 2001.
doi:10.2528/PIER00011001

2. Ghosh, S., P. K. Jain, and B. N. Basu, "Analytical exploration of new tapered-geometry dielectric-supported helix slow-wave structures for broadband TWT's ," Progress In Electromagnetics Research, Vol. 15, 63-85, 1997.
doi:10.2528/PIER95011200

3. Basu, B. N., Electromagnetic Theory and Applications in Beamwave Electronics, World Scientific, Singapore, 1995.

4. Sinha, A. K., R. Verma, R. K. Gupta, L. Kumar, S. N. Joshi, P. K. Jain, and B. N. Basu, "Simplified tape model of arbitrarily-loaded helical slow-wave structures of a traveling-wave tube," IEE Proc. PT-H, Vol. 139, 347-350, 1992.

5. Ghosh, S., P. K. Jain, and B. N. Basu, "Rigorous tape model analysis of inhomogeneously loaded helical slow-wave structures," IEEE Trans. Electron Devices, Vol. 44, 1158-1168, 1997.
doi:10.1109/16.595945

6. Ghosh, S., A. K. Sinha, S. N. Joshi, P. K. Jain, and B. N. Basu, "A heuristic analysis for a dielectric loaded tape helix considering the non-uniformity of the radial propagation constants over the structure cross sections ," Int. Jour. Electronics, Vol. 88, 197-213, 2001.
doi:10.1080/00207210010002032

7. Jain, P. K. and B. N. Basu, "The inhomogeneous loading effects of practical dielectric supports for the helical slow-wave structure of a TWT," IEEE Trans. Electron Devices, Vol. 34, 2643-2648, 1987.
doi:10.1109/T-ED.1987.23366

8. Kravchenko, N. P., L. N. Loshakov, and Y. N. Pchel'nikov, "Computation of dispersion characteristics of a spiral placed in a screen with longitudinal ribs ," Radio Engineering & Electronic Physics, Vol. 32, 33-39, 1976.

9. Kumar, L., R. S. Raju, S. N. Joshi, and B. N. Basu, "Modeling of a vane-loaded helical slow wave structure for broad-band travelling-wave tubes," IEEE Trans. Electron Devices, Vol. 36, 1991-1999, 1989.
doi:10.1109/16.34282

10. Paik, S. F., "Design formulas for helix dispersion shaping," IEEE Trans. Electron Devices, Vol. 16, 1010-1014, 1969.
doi:10.1109/T-ED.1969.16901

11. Lei, W., Z. yang, L. Liao, and P. Liao, "Analysis of a U-shaped vane-loaded helical slow-wave structure for wideband travelling wave tubes," Int. Jour. Electronics, Vol. 92, 161-172, 2005.
doi:10.1080/00207210512331337703

12. Jung, S. S., C. W. Baik, S. T. Han, S. G. Jeon, H. J. Ha, A. V. Soukhov, B. F. Jia, G. S. Park, H. S. Kim, H. S. Uhm, and B. N. Basu, "Wide-band semivane and heavily dielectric loaded helix traveling-wave tubes ," IEEE Trans. Plasma Science, Vol. 30, 1009-1015, 2002.
doi:10.1109/TPS.2002.801660

13. Zhu, Z., B. Jia, and Z. Luo, "Calculation of high-frequency characteristics for ridge-loaded helical slow-wave structure," Proceedings IEEE Int. Vacuum Electronics Conf. (IVEC-2008), 113-114, 2008.

14. Kory, C. L., Validation of an accurate three-dimensional helical slow-wave circuit model , NASA Contract Report 4766, NAS3-27600, March 1997.

15. Zhang, Y., Y. L. Mo, J. Q. Li, and X. L. Zhou, "Modelling of finite size vane-loaded helical slow-wave structures," IEE Proceedings --- Microwaves and Antenna Propagation, Vol. 151, 135-142, 2004.

16. Yang, J., Y. Zhang, X. Cai, and L. Li, "Study on effect of different metallic vane-loaded helix slow-wave structure in travelling-wave tubes ," Jour. Infrared Millimeter Terahertz Waves, Vol. 30, 611-621, 2009.
doi:10.1007/s10762-009-9476-8

17. Sensiper, S., "Electromagnetic wave propagation on helical structures," Proc. IRE, Vol. 43, 149-161, 1955.
doi:10.1109/JRPROC.1955.278072

18., HFSS10.0 User's Manual, Ansoft Corporation, Pittsburgh.
doi:10.1109/JRPROC.1955.278072

Dr. R. Seshadri

Dr. Sanjay Kumar Ghosh

Dr. A. Bhansiwal

Dr. S. Kamath

Dr. Pradip Kumar Jain