volume | PIER Journals

Abstract

The Lienard-Wichert potentials show that radiation is caused by charge acceleration. The question arises about where charge acceleration occurs on the most basic of antennas, a center-fed, perfectly conducting dipole, for which there are two obvious causes. One is the feeedpoint exciting voltage that sets into motion an outward-propagating charge and current wave at light speed c in the medium. A second is at the dipole ends where the outgoing wave is totally reflected producing a change in charge speed of 2c. A third is the decreasing amplitude of the propagating wave with distance due to its partial reflection along the wire. That reflected charge also undergoes a speed change of 2c. This is the reason why the decay of current flowing along a straight wire antenna has been attributed as being due to radiation. Radiation caused by these and other kinds of charge acceleration due to resistive loads, right-angle bends, and radius steps are investigated. These phenomena are examined primarily in the time-domain where they are more observably separable in time and space than in the frequency domain. The current and charge induced on an impulsively excited wire antenna and its broadside radiated E-field are computed using a time-domain, integral-equation model. The computed results are used to derive a numerical relationship between the amount of accelerated charge and its radiated field. This relationship is denoted as an Acceleration Factor (AF) that is obtained for various charge-accelerating features of a generic wire object are normalized to that of the exciting source for comparison with their respect speed changes.

1. Panofsky, W. K. H. and M. Phillips, Classical Electricity and Magnetism, Addison-Wesley Publishing Company, Inc., 1955.

2. Martin, R. G., A. R. Bretones, and S. G. Garzia, "Some thoughts about transient radiation by straight thin wires," IEEE Antennas and Propagation Society Magazine, Vol. 41, No. 3, 24-33, 1999.
doi:10.1109/74.775245 Google Scholar

3. Bantin, C. C., "Radiation from a pulse-excited thin wire monopole," IEEE Antennas and Propagation Society Magazine, Vol. 43, No. 3, 64-69, 2001.
doi:10.1109/74.934903 Google Scholar

4. Schelkunoff, S. A., Advanced Antenna Theory, 190, John Wiley & Sons, 1952.

5. Manneback, C., "Radiation from transmission lines," AIEE Journal, Vol. 42, 95-105, Feb. 1923. Google Scholar

6. Jackson, J. D., Classical Electrodynamics, 401, John Wiley & Sons, 1962.

7. Yeh, Y. S. and K. K. Mei, "Theory of conical equiangular-spiral antennas Part II — Current distributions and input impedances," IEEE Trans. AP-S, Vol. 16, No. 1, 14-21, 1968.
doi:10.1109/TAP.1968.1139111 Google Scholar

8. Shen, L.-C., T. T. Wu, and R. W. P. King, "A simple formula of current in dipole antennas," IEEE Trans. AP-S, Vol. 16, No. 5, 542-547, 1968.
doi:10.1109/TAP.1968.1139241 Google Scholar

9. Bach Anderson, J., "Admittance of infinite and finite cylindrical metallic antenna," Radio Science, Vol. 3, No. 6, 607-621, 1968.
doi:10.1002/rds196836607 Google Scholar

10. Jones, D. S., Methods in Electromagnetic Wave Propagation, 295, Clarendon Press, 1994.
doi:10.1109/9780470545256

11. Kudrin, A. V., E. Yu. Petrov, G. A. Kyriacou, and T. M. Zaboronkova, "Insulated cylindrical antenna in a cold magnetoplasma," Progress In Electromagnetics Research, Vol. 53, 135-166, 2005.
doi:10.2528/PIER04090101 Google Scholar

12. Jackson, J. D., "How an antenna launches its input power into radiation: The pattern of the Poynting vector at and near an antenna," Am. J. Phys., Vol. 74, 280-288, 2006.
doi:10.1119/1.2063069 Google Scholar

13. Kordi, B., R. Moini, and V. A. Rakov, "Comment on ‘Return stroke transmission line model for stroke speed near and equal that of light’ by R. Thottappillil, J. Schoene, and M. A. Uman," Geophys. Res. Lett., Vol. 29, No. 10, 1369, 2002.
doi:10.1029/2001GL014602 Google Scholar

14. Kordi, B., R. Moini, and V. A. Rakov, "Comparison of lightning return stroke electric fields predicted by the transmission line and antenna theory models," Proc. 15th Int. Zurich Symp. Electromagn. Compat., 551-556, 102P2, Zurich, 2003. Google Scholar

15. Baba, Y. and M. Ishii, "Characteristics of electromagnetic return-stroke models," IEEE Trans. Electromagn. Compat., Vol. 45, No. 1, 129-135, Feb. 2003.
doi:10.1109/TEMC.2002.808037 Google Scholar

16. Baba, Y. and V. A. Rakov, "On the mechanism of attenuation of current waves propagating along a vertical perfectly conducting wire above ground: Application to lightning," IEEE Transactions of Electromagnetic Compatability, Vol. 47, No. 3, Aug. 2005. Google Scholar

17. Miller, E. K., "The differentiated on-surface poynting vector as a measure of radiation loss from wires," IEEE Antennas and Propagation Society Magazine, Vol. 48, No. 6, 21-32, Dec. 2006.
doi:10.1109/MAP.2006.323341 Google Scholar

18. Smith, G. S., An Introduction to Classical Electromagnetic Radiation, Cambridge University Press, 1997.

19. Landt, J. A., E. K. Miller, and M. Van Blaricum, "WT-MBA/LLL1B (TWTD): A computer program for the time-domain electromagnetic response of thin-wire structures,", Lawrence Livermore Laboratory Report No. UCRL-51585, 1974. Google Scholar

20. Burke, G. J., E. K. Miller, and A. J. Poggio, "The numerical electromagnetics code (NEC) — A brief history," 2004 IEEE Int. Antennas Propagat. Symp. Dig., Vol. 42, 2871-2874, 2004.
doi:10.1109/APS.2004.1331976 Google Scholar

21. Miller, E. K. and G. J. Burke, "A multi-perspective examination of the physics of electromagnetic radiation," Applied Computational Electromagnetics Society Journal, Vol. 16, No. 3, 190-201, 2001. Google Scholar

22. Miller, E. K., "Time-domain far-field analysis of radiation sources," IEEE Antennas and Propagation Society Magazine, Vol. 53, No. 5, 46-54, Oct. 2011. Google Scholar

23. Balanis, C., Antenna Theory Analysis and Design, Harper and Rowe Publishers, 1082.

24. Miller, E. K. and J. A. Landt, "Direct time-domain techniques for transient radiation and scattering from wires," Proc. IEEE, Vol. 68, 1396-1423, 1980.
doi:10.1109/PROC.1980.11881 Google Scholar

Dr. Edmund K. Miller