20 Meter Ground Plane Vertical Antenna 
Input impedance is 50 ohms!! 
Here is the one I built 
This is a ground plane antenna for 20 meters. Radiating element is 217.5 inches long. Bottom of the transmitting element is 60 inches off the ground. There are 8 ground radials each 145.7 inches long are all tied together 54 inches above the ground. The radiator is 1 inch aluminum pipe using 12 ga wire as the ground plane.
Here are the Far field plots for this antenna 
Great for DX
SWR plot for 800 kHz bandwidth 14.0 - 14.4 MHz 
SWR is less than 1.2 for the entire 20 Meter band
Current Field for 20 Meter Vertical Antenna
20 Meter Vertical Z plot form 14.0 through 14.4 MHz 
Antenna is matched for 50 ohm feed line.
Click on link below to download the antenna model file. 
Webpage design by  KC0ONR 
Marshall County Alabama Repeater Systems