VERTICAL LOOP DIPOLE ANTENNA FOR 20 METERS
Here is a vertical dipole loop antenna close to ground. These are the
dimensions in feet. Each wire is modeled using 30 segments and #14 wire.
This is what the antenna looks like. Note that the feed for the dipole
is near the bottom. This may seem strange but the current distribution for
the folded dipole portion of the antenna is nearly linear. The feedpoint
can be anywhere along that portion. The bottom of the antenna is 0.2 feet
above ground. If you compare this antenna to the folded dipole loop in free
space, you will note that it is smaller. There is significant capacitive loading
to ground which explains why the antenna is smaller. As the antenna approaches
the earth, the driving impedance also rises. To counteract this tendency,
I shortened the folded dipole section to bring the impedance to 50 ohms.
The gain of this antenna is about 2 dB below the version that has 8 radials.
A 1:1 balun coil should be used at the feedpoint.
This is the elevation pattern.
This is the azimuth pattern at 29 degrees. Note that it is almost circular.
Here is a 3D plot
To return to LIMITED SPACE ANTENNAS go to:
LIMITED SPACE ANTENNAS
