RE: NEC-LIST: Zero-Q antenna

Hi Alan,

I regret that I cannot provide the details that you would like, but most of
these errors are imbedded in equations that I cannot easily reproduce.
However, these are just some of the points that Collin raises.

-Grimes & Grimes attempt to find the integral of the time dependent Poynting
vector over a spherical surface without the need to consider the detailed
expressions for the energy density in the field; this leads to smaller
minimum values for the Q of small antennas.

-One of their eguations requires a complex Poynting vector that cannot be
derived from Maxwell's equations; thus one would question the validity of
their theory.

-Their continuity equation is not a correct equation for expressing
conservation of power since it cannot be derived from Maxwell's equations.

-Their expression for stored energy is non-analytic and this is not possible
in free space. It can be shown that this leads to a negative time average
traveling energy density per unit length in certain regions which is
non-physical.

In summary the two fundamental errors that they make are the use of
incorrect energy conservation laws and the criteria for choosing the
constant of integration for the indefinite integral of dW/dt.
Although the methods for finding minimum Q are well established, Grimes &
Grimes have obtained results that contradict those that have been reported
by previous investigators such as Chu, Harrington, Fante and Collin and
Rothchild.

Best regards,

Ed

-----Original Message-----
From: alan.boswell_at_baesystems.com [mailto:alan.boswell_at_baesystems.com]
Sent: Tuesday, January 21, 2003 8:52 AM
To: Edward.Altshuler_at_hanscom.af.mil; nec-list_at_gweep.ca
Subject: RE: NEC-LIST: Zero-Q antenna

Ed
I am ready to believe what you say but it would be helpful if you could
summarise the main points of the Collin paper saying why you think the
Grimes papers are faulty.
Thanks
Alan

-----Original Message-----
From: Altshuler Edward E Civ AFRL/SNHA
[mailto:Edward.Altshuler_at_hanscom.af.mil]
Sent: 21 January 2003 13:27
To: 'alan.boswell_at_baesystems.com'; ccc_at_space.mit.edu; nec-list_at_gweep.ca
Subject: RE: NEC-LIST: Zero-Q antenna

Dear Colleagues,

Unfortunately the Grimes & Grimes papers are filed with misconceptions and
errors that lead them to invalid results. For those who are interested I
refer you to an excellent paper by Prof. Robert E. Collin on "Minimum Q of
Small Antennas," Journal of Electromagnetic Waves and Applications, Vol. 12,
1369-1393, 1998.

Ed Altshuler

-----Original Message-----
From: alan.boswell_at_baesystems.com [mailto:alan.boswell_at_baesystems.com]
Sent: Monday, January 20, 2003 4:51 AM
To: ccc_at_space.mit.edu; nec-list_at_gweep.ca
Subject: RE: NEC-LIST: Zero-Q antenna

Chuck
Quote: An ensemble of four dipoles, two electric and two magnetic ones, one
of each type lying along each of the x- and y-axes. More details are said
to be in the 2000 paper in MOT Letters. They say there is strong intermodal
coupling between the x-directed electric moment and the y-directed magnetic
moment, and vice versa (I think that's questionable).
Alan
 

-----Original Message-----
From: Chuck Counselman [mailto:ccc_at_space.mit.edu]
Sent: 17 January 2003 18:05
To: alan.boswell_at_baesystems.com
Subject: Re: NEC-LIST: Zero-Q antenna

At 2:01 PM +0000 1/17/03, alan.boswell_at_baesystems.com wrote:
>Has anyone seen / modelled / experimented with the "zero-Q antenna"
>proposed by Grimes et al in Microwave and Optical Technology
>Letters, vol. 28 no. 3, Feb. 5, 2001, also in vol. 27 pp. 53-58
>(2000)?

I haven't; sorry; but I wish, and I bet others do, too, that you
would post a summary of what it is and how it works, to the list.

Tnx -chuck.

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