[Antennas] True Ground Plane?

Wed, 27 Mar 2002 22:35:14 -0800

the arrl handbook also describes a "ground plane" as being mounted on the
ground  as  well but requiring more radials than if installed at height.
ground plane simply describes an artificial ground  formed by many radials
to simulate actual ground without the inherent losses.

----- Original Message -----
From: "Ron W7MRR" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Wednesday, March 27, 2002 9:57 PM
Subject: RE: [Antennas] True Ground Plane?

>
> Sure Ron.
>
> As Bill Orr described, a ground plane is a vertical halfwave antenna, fed
at the center, with the bottom half of the dipole divided into separate
sections which are swung up to the horizonal plane.  The vertical section
acts as an antenna and the horizontal portions, or radials, form an
artifical ground plane.  The horizonal radials of the ground plane antenna
perform two important jobs.  First, they provide a return system or image
for the radio field of the vertical quarter wave antenna.  The engery field
flows between the antenna and the radials.  Secondly, the radials shield the
ground plane from the nearby ground with its attendant ground losses.  The
degree of shielding and the amount of ground loss depend upon the number of
radials used and the electrical height of the ground plane above the surface
of the actual ground.
>
> As I stated earlier, the higher you elevate your radials the less ground
loss you should experience with the antenna.  According to the ARRL antenna
book, "There is no advantage to using more than four or five radials if the
[ground plane] antenna is elevated a half wavelength or more above the
ground."  As you can see, it's all about avoiding ground losses.  If you are
not avoiding ground losses, you have something less than a "true ground
plane."
>
> If you are still puzzled, suggested reading would include the empiricial
evidence found in an article written by KB8I in August, 1988 for QST
entitled, "Elevated Vertical Antenna Systems" and "Elevated Radial Systems"
by K0CS in Vertical Antenna Theory - The Low Band Monitor (7/94).
>
> Ron W7MRR
>
>
> --- On Wed 03/27, Ron Evans  wrote:
> > Ron, while I agree with nearly everything you said, I find the term
> > "true ground plane" puzzling.  Perhaps you can share with the
> > list
> > members your authority for the assertion that a ground plane must be at
> > least 1/2 wavelength off the ground to be...a "true ground
> > plane."
> >
> > The ARRL Antenna Book imposes no such restriction.  Straighten us out?
> >
> > 73,
> >
> > Ron - K5MVR
> >
> >
> >
> > "What you have now is a vertical with elevated radials.  You have to
> > go
> > at least 1/2 wavelength off the ground on your chosen band to be able to
> > categorize the antenna as a true ground plane."
> >
> >
> >
> >
> >
> > - - -
> >
> > Your moderator for this list is:
> > Larry Wilson KE1HZ [email protected]
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