F. Nekoogar, Ultra-Wideband Communications: Fundamentals and Applications. Upper Saddle River, NJ: Prentice Hall Press, 2005.
 K. Siwiak and D. McKeown, Ultra-Wideband Radio Technology. Chichester, West Sussex: John Wiley & Sons, Ltd., 2004.
 A. Grebennikov, RF and Microwave Power Amplifier Design. New York, NY: McGraw-Hill, 2005.
 A.S.Gilmour, Jr. Principle of Traveling Wave Tubes, Magnetrons, Crossed-Field, Amplifiers, and Gyrotron, Boston, Artech House, 2011.
 L. Hongtao, “Slow-wave characteristics of any shape spiral groove and has a central dielectric rod spiral groove,” M.S. thesis, School of Physical Electron., Univ. of Electron. Sci. and Tech., Sichuan, China, 2006.
 M. K. Alaria, A. Bera, R. K. Sharma, and V. Srivastava, “Design and Development of Helix Slow-Wave Structure for Ku-Band TWT,” IEEE Trans. Plasma Science, vol. 39, no. 1, pp. 550-554, Jan. 2011.
 F. He, J. Luo, M. Zhu, and W. Guo, “Theory, Simulations, and Experiments of the Dispersion and Interaction Impedance for the Double-Slot Coupled-Cavity Slow Wave Structure in TWT,” IEEE Trans. Electron Devices, vol. 60, no. 10, pp. 3576-3583, Oct. 2013.
 A.S. Gilmour, Jr. Principle of Traveling Wave Tube, Boston London, Artech House, 1994.
 A. Singh, J. E. Scharer, J. H. Booske, and J. G. Wohlbier, “Second- and third-order signal predistortion for nonlinear distortion suppression in a TWT,” IEEE Trans. Electron Devices, vol. 52, no. 5, pp. 709-717, May 2005.
 Y. Hu, Y. Wang, Z. Yang, J. Li and B. Li, “Harmonic reduction for broadband helix TWTs with negative dispersion,” IVEC 2012, Monterey, CA, 2012, pp. 231-232.
 T. K. Ghosh, A. J. Challis, A. Jacob, D. Bowler, and R. G. Carter, “Improvements in Performance of Broadband Helix Traveling-Wave Tubes,” IEEE Trans. Electron Devices, vol. 55, no. 2, pp. 668-673, Feb. 2008.
 E. Gehrmann, P. Birtel, W. Dürr, and A. F. Jacob, “Filter Helix for Harmonic Suppression in Traveling Wave Tubes,” IEEE Trans. Electron Devices, vol. 61, no. 6, pp. 1859-1864, June 2014.
 F. K. Mullen, “Traveling-wave tubes with ferrite attenuators,” IRE Trans. Electron Devices, vol. 8, no. 4, pp. 284-289, July 1961.
 A. Karp and W. R. Ayers, “Design concepts for an octave-bandwidth coupled-cavity TWT,” International Electron Devices Meeting, 1978, vol. 24, pp. 546-549.
 D. M. Pozar, Microwave Engineering, 2nd ed. New York: John Wiley & Sons, Inc., 1998.