[TowerTalk] vertical antenna ground loss

[Its from Onion]

For the purpose of calculation, it is convenient to consider that the reflected wave is generated not by reflection, but rather by an "image" antenna located below the surface of the ground.  The image antenna  is so chosen that the joint action of the actual antenna and its image produces the same conditions  in the space above the earth as exist with the actual antenna in the ground.

This result requires that the image antenna have the same physical configuration that is the mirror image of the actual antenna.

The effect of the ground (coefficient disregarded for this discussion) on the directional characteristic of an antenna can be obtained by considering that the antenna together with its image forms a simple two-element antenna array, spaced a distance equal to twice the height of a actual antenna center above ground. 


Does that help any?

Lee
KE4VYN



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I have difficulty in accepting the explanation of poor vertical antenna 
performance due to ground loss.It seems to be the culprit in about all 
antenna books going way back in years but is never explained. My 
understanding is that verticals do not get the benefit of ground reflection 
that horizontals get; that the radiation of the wave may be partially 
absorbed on its path away from the antenna but this occurs not within the 
area that radials woul alleviate.

This leaves the radials as providing a better return path for the return 
currents.  However, it is my understanding that antennas radiate because of 
the changing (accelerating) current in them which means that the antenna is 
charging and discharging,  If this is the case then the charging and 
discharging has to be offset with something that is of the opposite 
polarity.  That something in the case of the vertical is the ground if there 
are no radials.

When radials are added, the antenna itself can better charge and discharge 
which is the real problem with the ground resistance
being only an inhibiter?

Any corrections or explanations is welcome.

k7puc