HERE IS A DESIGN FOR A GROUND MOUNTED VERTICAL WITH SIX SECTIONS FOR 20 METERS
Theory:
The idea for this design came from N2DT. He suggested that I use several sections of my vertical folded monopole loop in an effort to reduce the overall height of the antenna while retaining a 50 ohm driving impedance.
Here are the dimensions in millimeters.
This is what the antenna looks like:
Side View
Rotated Side View
Here is a 3D view of the antenna:
Here is a 2D plot:
Sorry but it didn't all fit. The pattern is symmetrical.
Note that there is a nice deep null at the top which means that noise will be low on receive. The angle of maximum radiation is 19 degrees, which is 9 degrees lower than the original monopole design. This is a bonus that I was not expecting.
Here is a 3 D pattern:
Here is the legend for the above plot:
Note that the SWR is good. Maximum radiation of 3.92 dBi is very good for such a small antenna.
Here is an SWR plot:
Some of this was cut off but the top is very close to 2:1 SWR. This antenna will not cover the entire band without a tuner but most of it.
You are probably wondering what the point of all this is. The idea is to make an antenna that is as compact as possible, has a reasonable bandwidth, and a low angle of radiation. This antenna is only about 3 feet high and 10 feet in diameter not counting the radials. More sections can be added. Each time, the height will decrease, the diameter will increase, and the bandwidth will decrease. This assumes that you want to maintain a 50 ohm driving impedance.