Re: NEC-LIST: cross field antennas

Delivered-To: john.belrose_at_crc.ca
Date: Tue, 9 Feb 1999 17:37:29 -0500
From: Grant Bingeman <DrBingo_at_compuserve.com>
Subject: Re: cross field antennas
Sender: Grant Bingeman <DrBingo_at_compuserve.com>
To: John Belrose <john.belrose_at_crc.ca>
MIME-Version: 1.0

Dear Jack, thank you very much for your considered reply. I must say
my feeling is that this antenna belongs in the perpetual motion
machine museum. I brought up the same question with another CFA
experimenter of how much radiation was contributed by his attic
"ground" wires. He didn't know.

I would like your permission to forward your reply to a colleague of
mine at Hatfield and Dawson, a consulting engineering firm. Ben
Dawson has an interest in these antennas, and would like to put the
efficiency claims to bed with some rigorous and repeatable
measurements.

I would also appreciate it if you could convey your opinion to Jack at
Antennex, the on-line antenna magazine. I have forwarded a note from
one of his authors, which you may find interesting. Your decades of
experience with electrically short antennas carries a lot of weight,
and your opinion re the CFA concept would be respected by those who
appreciate good science.

Grant Bingeman
---------------------------------------------
Delivered-To: john.belrose_at_crc.ca
Date: Wed, 10 Feb 1999 10:41:51 -0800
From: Roy Lewallen <w7el_at_teleport.com>
Organization: EZNEC Antenna Analysis Software
To: John Belrose <john.belrose_at_crc.ca>
Subject: Re: NEC-LIST: cross field antennas

Hello Jack,

There's been discussion from time to time about the CFA on the
rec.radio.amateur.antenna newsgroup, and I frequently point out the
conspicuous lack of quantitative data on the thing as an indication of
its probable worth. Would you mind if I posted a copy of your NEC-LIST
posting on that group? I'll post it entirely intact and properly
credited.

73,
Roy, W7EL
---------------------------------------------

Dear Grant, Roy, and many others,

For purposes of copying my comments to readers outside those on the
NEC-List, we need to go back to the original TC I posted, on 15
November 1995, so as to provide a beginning --- and to add other
references that have emerged as a result of my recent posting.

Please copy to whoever, since this might stimulate further thinking
about the antenna, and what is needed is additional performance
measurements.

And, thank you all for the interesting mail on the subject.

73, Jack, VE2CV

-------------------------------------------

The Cross-Field Antenna
Should we go for it or let it Rest in Peace?
_____________________________________________

An antenna is sometimes described as a coupling device, coupling
electromagnetic energy to space, and following on with this line of
thinking, antenna amateurs/specialists have wondered whether there
were methods of achieving this process in more efficient ways than
provided by use of monopoles, dipoles and loops. The performance of
electrically small antennas is a subject that has been of interest for
me for more than 50-years.

For example, can we devise an antenna system that will radiate only a
true Zenneck-wave, and thus provide extended ground-wave coverage,
without the interference effects of a skywave. The answer to this
query is no. Since a spacewave arriving tangentially at the surface
of the earth will generate a ground wave, a ground wave will most
certainly generate a spacewave. And, concerning more efficient
coupling to the propagation media, most ideas that have so far emerged
are hoaxes. In one, where one considers an antenna as an opened out
transmission line, it is claimed that the characteristic impedance of
the antenna should be made equal to the intrinsic impedance of free
space (377 ohms). This is nonsense. In another, it is claimed that
the antenna's radiation resistance should be made equal to the
intrinsic impedance of free space. This latter statement has even
less meaning, since the antenna's radiation resistance for a specific
antenna depends on where you decide to reference it on the antenna
structure.

Continuing, in 1989 (see Electronics + Wireless World, March, July and
November, 1989, and December 1990) and in following years, Maurice C.
Hatley, GM3HAT describes a cross-field antenna (CFA), in which
quadrature E and H fields are separately generated. A follow on paper
[1] offered an explanation of its properties in terms of "Poynting
vector synthesis". In the words of the inventor, reversing the form
of Maxwell's equations led to the "realization and development of this
revolutionary new antenna system". Quite small versions of it have
(apparently) been fabricated and tested, cf. reference [1], to
demonstrate its ability to efficiently couple EM energy to space ---
but, notwithstanding, in my view this antenna also fits the category
of a hoax, since attempting to generate E X H in the antenna itself,
and claiming that such an antenna more effectively couples to the
space surrounding the antenna is about a fruitless as the other ideas
discussed above.

Proving beyond any doubt that a theory is completely wrong is very
difficult [c.f 2, and inventor's reply 3]. But it is possible to
conduct experiments as scientifically and impartially as possible, and
to draw firm and well founded conclusions from them under the test
conditions [4] --- but even here we have inconsistency --- since the
result obtained depends on who is doing the experiment, the inventor
or someone else.

The Hatley, Kabbary and Khattrab paper claims that the field strengths
and, service area for a small (1.6 percent of a wavelength high) MF
CFA in Egypt is identical to that provided by a 75 m quarter
wavelength vertical.

The Egyptian antenna is a ground-plane (GP) type CFA on the roof of
the transmitter building, and after listening to the presentation of
that paper, I questioned whether the radiation realized was in fact
generated by the GP CFA, or by currents flowing on the outside surface
of the coaxial cable feeding the antenna. I also wondered whether the
previously used quarter wave vertical antenna might indirectly
(induced currents and re-radiation) be a part of the antenna system.

At a more recent IEE ICAP Meeting (Edinburgh, April 1997), I was
presenting a paper on elevated radials, I met Hatley and his Egyptian
colleague (Khattrab), or should I say they cornered me; and I learned
that the Broadcaster was happily still using the antenna --- or should
I say the authors still believed in the results of their experiment
--- in retrospect I am not sure now which is which.

Maurice told me that he was developing HF versions of this antenna for
use by radio amateurs, for mobile communications, and he would send me
details on it. I told him I would be glad to measure the radiation
efficiency of his amateur version --- but, no correspondence or offer
of an antenna has to date been received.

In 1992 Colin Davis, University of Surrey [4], conducted a study of a
VHF dipole version of the CFA, his model was a 50-percent scaling of
Hatley's original antenna. His work, carried out to investigate
whether the CFA does operate as an efficient radiator, casts doubts
about it, which seem overwhelming.

Despite his best efforts to make it work, the best Davis could
achieve, with respect to gain was - 23 dBd ["The great tragedy of
science --- the slaying of a beautiful hypothesis by an ugly fact",
T.H. Huxley].

The article by Davis starts off by a consideration of the impedance of
the antenna, since power cannot be successfully coupled to the antenna
unless its impedance is known. Little information is available in the
literature to indicate what value this might be. It is interesting to
note that a discussion with Hately [Davis-Hately, private
communications], suggested that both input impedances of the CFA
antenna (E-plate and D-Plate parts of the antenna) should be around
300 ohms --- clearly referencing performance to the intrinsic
impedance of free space.

Smith [5] has considered input impedance. He considers that the
E-plates should have the characteristic impedance of an electrically
small dipole; and the D-plates are nothing more than a capacity, the
D-plates having a similar capacitive reactance to the E-plates. Smith
also concludes that there is nothing magical about the cross-field
antenna, since it will encounter the same efficiency-bandwidth
limitation, as for any electrically small antenna [6].

And, Smith makes reference to my article [7] which reveals that the
hula-hoop antenna (earlier called the DDRR antenna) is nothing more
than a resonate inverted-L --- and so the efficiency of this antenna
becomes vanishing small as the height (above the ground plane) of the
horizontal part of the hula-hoop becomes small.

So, in conclusion, is the debate concluded --- should the CFA RIP?

73, John S. (Jack) Belroser, PhD. Cantab, VE2CV
john.belrose_at_crc.ca
10 February 1999

References

1. M.C. Hately, F.M. Kabbary and Khattab, "An Operational MF Antenna
using Poynting Vector Synthesis", Proceedings of 7TH International
Conference on Antennas and Propagation, Part 2, Conference Publication
No. 333, April 1991, pp. 645-648.

2. K. Donaldson, "Misguided CFA", Electronics World+Wireless World,
October 1992, pp. 837-838.

3. M.C. Hately, "CFA -- no tricks", Electronics World+Wireless World,
December 1992, p. 1007.

4. Colin Davis, "CFA --- RIP?", Electronics World + Wireless World,
May 1993, pp. 405-407.

5. M.S. Smith, "Conventional Explanation for 'Crossed Field Antenna'",
Electronic Letters, 28, 13th February, 1992, pp. 360-361.

6. H.A. Wheeler, "Fundamental limitations of small antennas",
Proc. IRE, 35, 1947, pp. 1479-1484.

7. J.S. Belrose, "Transmission line low profile antennas", QST,
December 1975, pp. 19-25.

8. J.M. Boyer, "The Hula-hoop antenna: a coming trend?", Electronics,
11, January, 1963, pp. 44-46.

_____________________________________________
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>
_____________________________________________
Received on Wed Feb 10 1999 - 20:22:28 EST