Re: NEC-LIST: radiation from dipole

Hal Smith wrote:
>
> Food for thought with regards to the source of radiation. A Physics
> professor of mine (probably during my graduate E&M course at
> Roosevelt in Chicago) once gave a class lecture in which he derived
> Maxwell's Equations from Einstein's Special Relativity. The real
> physical situation concerning electromagnetic radiation is MUCH more
> complicated than the models we normally use. The true source of
> radiation is apparently tied up with the concepts of Special
> Relativity like time dilation, relativistic energy, and dimension
> distortion.

Hal,

I have just returned to my office after being away for more than a
month. I see a topic which I more or less started is still ongoing.

You are perfectly correct.

I copy below the beginning para from a paper I have recently written
concerned with the history of wireless telephony --- intended for the
AP-S/URSI AP 2000 meeting in Salt Lake City, UT, 16-21 July.

"The very possibility of wireless communications is founded on the
researches of Maxwell, since his equations form the basis of
computational electromagnetics. Their correctness was established by
Hertz, when in 1887 he discovered EM radiation at UHF frequencies as
predicted by Maxwell. Since the pioneering work of Maxwell beginning
in the middle 1850s, and of his followers, a small group that became
known as Maxwellians, which included UK's Poynting and Heaviside,
Maxwell's equations have been studied for over a century, and have
proven to be one of the most successful theories in the history of
radioscience. For example, when Einstein found that Newtonian
dynamics had to be modified to be compatible with his special theory
of relativity, he found that Maxwell's equations were already
relativistically correct. EM field effects are produced by moving
charges, and so Maxwell had automatically built relativity into his
equations."

But, that is about as far as I can go. I would be interested to read
a paper along the lines of your Professor's way of thinking.

My post graduate University courses on electromagnetics was based on
Ed Jordan's book Electromagnetic Waves and Radiating Systems,
Prentice-Hall, 1950. He discusses (pp. 303-308) radiation from wires
in terms of an alternating current element or oscillating electric
dipole (a chain of Herzian dipoles).

For those interested in this subject, Glenn Smith, Georgia Institute
of Technology, has recently published a paper entitled "Teaching
Antenna Analysis from a Time-Domain Perspective", paper number 0425,
Millennium Conference on Antennas and Propagation (Davos,
Switzerland), 9-14 April, 2000.

This paper is clearly a progress report. He considers radiation due
to a moving point charge for dipole type antennas --- but his
concluding remarks interestingly suggest that more is to come. He
briefly introduces the subject of more complicated antennas: a
circular loop. Here, in the author's words, "the radiation is
analogous to that for a moving point charge, only now there is also
radiation from the curvature of the antenna, which corresponds to
synchrotron radiation from a charge moving on a circular trajectory."

It is interesting that this subject is still under discussion after
150 years.

Regards, Jack

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
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Received on Sun May 07 2000 - 20:18:21 EDT