Radials and the vertical antenna

Antennas claiming no radials or counterpoise needed are simply half an antenna.The current needs a return path and without radials or a counterpoise to supply that path will usually end up using the coax braid to do so.We don't really want the coax shield to radiate or indeed be part of the antenna and this is the reason many vertical antennas have chokes at the feedpoint of the antenna. Some designs however work on this principle of using the coax shield as part of the antenna.

I was in discussion with a respected amateur and antenna designer steve G3TXQ regarding radial placement at the base of a vertical antenna.I was interested to know if laying radials in a strategic manner could have any influence on the direction of strongest signal.Most people know a vertical is omni directional ,that is the signal is radiated and recieved 360 degrees around the antenna and most of us will try and lay radials around that 360 degrees at the base of the antenna at varying lengths depending on the available room we have in an attemp to get this omni directional effect and good current return.So can we manipulate the signal pattern of a vertical antenna by strategically placing radials down in an attempt to null any troublesome directions and concentrate on wanted signals?. Below is an explination, when the term quadrant is used imagine the 360 degrees around the base of the antenna devided into four.Each segment is a quadrant.

Ground has two separate affects on the performance of a vertical: 1) Close-in, it affects the losses incurred by the displacement currents which flow from the vertical and through the ground back to the feedpoint. If we have many more radials in one quadrant than another, the losses will be significantly less for the displacement current flowing from the antenna in that direction. So if I model 16 radials in one quadrant, with none in the other 3 quadrants, and assume very poor ground conductivity there is a very big difference between the losses in the various directions - I see almost 10dB of "front-to-back" at some take off angles. But if I do the same thing over salt water there is no "front-to-back" because the radials are not significantly improving the conductivity in their direction - the conductivity is already very good. But I say again, this "front-to-back is not leading to any real Gain - it's more a case of "more-loss" in the direction where we haven't placed the radials. Just to put some numbers on it: if you were prepared to put down say, 16 quarter-wave radials, and were only interested in one quadrant, the difference between 16 radials spread all around and 16 in one quadrant would be about 0.5dB in the wanted direction and a F/B of 4dB. That's over "average ground". In other words, the increased density of radials has improved things by 0.5dB in the wanted direction, and the absence of any radials in the other 3 quadrants has increased losses in the reverse direction by 3.5dB. 2) At the distance from the antenna where ground reflections take place, the ground conductivity and dielectric constant affect the relative power at different take-off angles. This is usually at a distance from the antenna where our radials don't reach, so we can't influence things there. As I'm sure you know, salt water has the highest conductivity and will result in low take-off angles. As an extreme example, a vertical set on the boundary of salt water and an extremely poor ground (say a concrete inductrial area) could show as much as 15db better signal in the seaward direction at low elevation angles.

Above you can see a plot for a quarter wave vertical antenna for 20m using quarter wave radials over poor ground. The blue line represents 64 equally spaced radials around the antenna.The red line represents 16 radials layed out in a single quadrant.Assuming we have an atenna over poor ground we could use this laying of radials in any given quadrant to our advantage in nulling to a degree all 3 other quadrants and so in effect giving some control over the direction of strongest signal.(not gain).This front to back could be very useful and radials placed strategically could actually be beneficial as could poor ground conductivity assuming we were looking for this f/b. So it looks like we can actually use strategically placed radials AND poor ground conductivity which is normally what we don't look for to our advantage. something that may be of use especially portable .