To: All
Subject: Need sanity check for one point of antenna theory
Here goes:
The gain of any antenna is referenced to a theoretical isotropic
radiator. A half wave resonant dipole (in free space) has a gain of 2.15 dB
over an isotropic source; hence it's rated at 2.15 dBi.
A quarter wave, end fed, monopole rod, erected normal to an infinite
ground plane, displays a field pattern equal to one lobe, or one half, of the
pattern formed by the dipole antenna. The ground plane serves as an image, or
mirror, of the other half of this resonant system.
So, the monopole directs the radiant energy into only one hemisphere
(above the ground plane), at the expense of no radiation into the other
hemisphere (below the ground plane). From the vantage point of those observers
located above the ground plane, the monopole creates a field with twice the
power of a dipole.
And, since twice the power is a 3 dB increase, then the gain of a
quarter wave ground plane rod is 3 dBd, or 5.14 dBi.
Uhhhh, right?
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Ed Price
[email protected]
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA. USA
619-505-2780
List-Post: [email protected]
Date: 07/16/97
Time: 12:53:09
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