I think most of the NEC based programs calculate the current distribution
along the length of the antenna's linear elements. The far field pattern of the
antenna can then be derived by integrating the field contributions of each
elemental portion of that distribution. The equations given in Kraus's
"Electromagnetics" 2nd edition express the E and H fields in the far field
in terms of the current distribution only. His text does mention that the
E field depends on both current and charge distribution, but that only the
current distribution needs to be considered in the far field.
A 1/2 wave dipole can be thought of as a bunch of short linear dipoles
placed end-to-end with the current in each short dipole element proportional
to the magnitude of the dipoles familiar half sinusoidal current distribution at
that point along the length of the antenna. The short dipole elements near the
center of this array will of course contribute more to the overall radiation
field
than the ones near the ends since the current will be larger in the elements
near the center than that of those near the ends.
If I had the choice between having the ends of my dipole high with the center
low versus having the center high and the ends low, I would choose the latter
option.
73 de Mike, W4EF........................
----- Original Message -----
From: "2" <2@vc.net>
To: "Ron Lile" <rel@rnet.com>; "at towertalk" <towertalk@contesting.com>;
"1topband mailing-list" <topband@contesting.com>
Sent: Sunday, September 02, 2001 9:18 PM
Subject: Re: [TowerTalk] True or Not True?
>
> >
> >Several papers have been published lately that attempt to explain the origin
> >of radiation from a dipole.
> >
> >The papers are saying that the primary radiation on a dipole come from the
> >middle (the high current point) AND the ends.
> >
> // I used to think that the radiation mostly came from the current
> portion of an antenna. However, the University of California currently
> teaches that all parts contribute equally. Electro Magnetic radiation -
> a.k.a. photons - consist of an electrostatic E-field and a perpindicular,
> electromagnetic H-field. The higher-voltage ends contributes most to the
> E-field and the higher-current center contributes most to the H-field.
> -- Congrats Ron Lile, KØRL, you were the only one who agrees with the
> University of California.
> cheers
>
> >The papers have been publish in the Journal for the Antennas and Propagation
> >Society of the IEEE. I need to look them up again in the library. They are
> >recent issues.
> >
> >Ron , K0RL
> >
> >
> >----- Original Message -----
> >From: 2 <2@vc.net>
> >To: at towertalk <towertalk@contesting.com>; 1topband mailing-list
> ><topband@contesting.com>
> >Sent: Sunday, September 02, 2001 9:39 AM
> >Subject: [TowerTalk] True or Not True?
> >
> >
> >>
> >> Does radiation come mainly from the high-current portion of an antenna --
> >> i.e., for a half-wave, from the center?
> >>
> >> - R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
> >> end
> >>
> >>
> >> List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
> >> Trylon Titan towers, coax, hardline and more. Also check out our self
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> >>http://www.anwireless.com
> >>
> >> -----
> >> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> >> Submissions: towertalk@contesting.com
> >> Administrative requests: towertalk-REQUEST@contesting.com
> >> Problems: owner-towertalk@contesting.com
> >>
> >
> >
> >List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
> >Trylon Titan towers, coax, hardline and more. Also check out our self
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> >
> >-----
> >FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> >Submissions: towertalk@contesting.com
> >Administrative requests: towertalk-REQUEST@contesting.com
> >Problems: owner-towertalk@contesting.com
> >
> >
>
>
> - R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
> end
>
>
> List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
> Trylon Titan towers, coax, hardline and more. Also check out our self
> supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|