Greetings to one and all,

Hopefully someone will be able to advise me on the following, being very
new to NEC modelling I've hit a stumbling block.

As part of my Masters dissertation (In RF Engineering) I am working on
developing an N element antenna array in the V/UHF area of the spectrum
for a field system (non-amateur). It's nothing that's not really been
done before, but I'm taking the practical 'ham' approach to it. Anyway
this is only background to my question, and is not really too relevant.

I decided to have a go with some modelling software before actually
building an array ad testing it. It just so happens that I had installed
4nec2 many moons ago though I'd never used it. For some reason I had it
in my head that modelling an antenna was difficult. Well I'm sure it
takes a lot of thought to do a complex model, and the simple models I've
done so far have been quite a learning curve, but a fun one at that.

Anyway, I have modelled what is essentially a 4-square above ground and
so on, which is fine. The next stage was to make the array out of
dipoles. This went fine when modelling in free space, centring around
z=0. I get lovely 3D plots etc, wonderful!

Now I want to model this dipole arrangement as if it was mounted on a
tower, i.e. not at z=0. So I move all the elements up to the correct
height and add in a real earth (which adds itself at z=0). That much is
fine. When I then run the model the radiation plots are still all
centred on z=0.

Now, logic says to me that the radiation should be coming from the
driven antenna elements rather than a point on the ground beneath them.

Am I missing something really simple here?

Many thanks in advance. :-)

--
73, Iain M0PCB/AD5XI

Hi Iain

You are displaying the far field radiation pattern, not the close-up
energy density...

ie the antenna and height above ground is very small compared to the
radiation pattern being displayed.

Cheers Bob

Iain Kelly wrote:


Now, logic says to me that the radiation should be coming from the
driven antenna elements rather than a point on the ground beneath them.

Am I missing something really simple here?

Many thanks in advance. :-)

Bob Bob wrote:
Hi Iain

You are displaying the far field radiation pattern, not the close-up
energy density...

ie the antenna and height above ground is very small compared to the
radiation pattern being displayed.

Cheers Bob

Aha, so it's just a matter of scale in the plot then? That's what was
confusing me. My mind was looking to directly compare the 3D pattern
generated with the antenna structure. It makes a bit more sense now.

Cheers,

--
73, Iain M0PCB/AD5XI