[BC] Ground system

[Richard Fry]

On Saturday 11 February 2012 02:23:40 pm Richard Fry wrote:
> But all of the useful, far-field radiation from a vertical monopole
> originates from the vertical section only, not from buried (or elevated)
> horizontal radials.

Cowboy answered, "Correct, the operative word being 'useful.'"

Another interesting point about a thin, linear, unloaded 1/4-wave vertical 
monopole with its base near a perfect ground plane*  -- it has an input 
impedance of 37.5 + j 21.25 ?, which is exactly half that of a 1/2-wave 
dipole in free space.

So for the same Z-matched power applied, twice the r-f current flows on the 
monopole as on each side of the 1/2-wave dipole, and the peak intrinsic 
directivities of those two radiator forms therefore are equal (2.15 dBi).

However the reflection of the radiation by the monopole from a perfect 
ground plane adds 3.01 dB of directivity to the net far field, for a maximum 
system gain of 5.16 dBi in the horizontal plane.

A monopole antenna system with 5.16 dBi gain in the horizontal plane 
produces a field intensity a bit over 313 mV/m at 1 km for 1 kW of applied 
power (perfect ground plane).

The theoretical field of a 1/4-wave monopole using 120 x 1/4-wave buried 
radials gets pretty close to that  -- usually around 305 mV/m.  This 
indicates a system radiation efficiency of about 95%.

    * which 120 x 1/2-wave radials can get pretty close to providing.

RF