[Antennas] True Ground Plane?

2002年3月28日 08:07:52 -0500 (Eastern Standard Time)

Ron,=0D
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Thanks. Even I understand it now.=0D
=0D
Bill KA8VIT=0D
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-------Original Message-------=0D
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From: [email protected]=0D
Date: Thursday, March 28, 2002 12:57:57 AM=0D
To: [email protected]; [email protected]=0D
Subject: RE: [Antennas] True Ground Plane?=0D
=0D
Sure Ron.=0D
=0D
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 fl=
ows
between the antenna and the radials. Secondly, the radials shield the gro=
und
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 t=
he
actual ground.=0D
=0D
As I stated earlier, the higher you elevate your radials the less ground
loss you should experience with the antenna. According to the ARRL antenn=
a
book, "There is no advantage to using more than four or five radials if t=
he
[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 ar=
e
not avoiding ground losses, you have something less than a "true ground
plane."=0D
=0D
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 System=
s"
by K0CS in Vertical Antenna Theory - The Low Band Monitor (7/94).=0D
=0D
Ron W7MRR
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