Re: NEC-LIST:coco curtains

Hey Giusseppe,

To strictly answer your question here's what the theory says:
If you have an array of similar antennas (collinear array in your case),
the radiation pattern will be the product (sum in dB) between the "array
factor" and the individual antenna pattern. In most cases the "array
factor" is the dominant factor.
Assuming the individual antenna patterns will not be significantly
modified due to coupling between the array's elements.

The array factor represents the pattern generated by isotropic point
sources, when each point is fed with a certain phase and amplitude.
So you may synthesize an array pattern with nulls the way you want, and
with a narrow beam (high gain) in a certain direction. That is easiest
done on paper or there should be some downloadable programs to do it.

Some problems may occur at low frequencies due to array size. The ground
may have an effect depending on how the antenna is mounted. Also the
feeding may be a problem, to get the desired phase relation and properly
match the elements.

In your figure you have horizontal dipoles. A short dipole radiates in
its plane (nulls along its longitudinal axis). Combine that with an
array that has a null inwards the screen (and ground if possible) and
main lobe outward the screen and there you are.

Then you may actually model and optimize the dimensions with NEC, or
just experiment.

I hope it helps.

Cornel Gazdaru

ROSSI Giuseppe wrote:

> Dear Listmember
>
> I wish to ask some help concerning antenna array.
> I'm a radio amateur and i wish to experiment with curtain of
> coaxial collinea antenna (coco).
>
> I wish to explore the feasibility of high gain non yagi antenna.
>
> For this reason i wish to built a curtain with high gain and with
> a reasonable front to back ratio.
>
> For mechanical reasons i intend to use two or more horizontal coco antenna
> laid
>
> in a vertical plane. To be more clear this is the sketch:
>
>
>
> vertical mast
> |
> ------|------ one coco
> |
> |
> ------|------ another coco
> |
>
>
> The question is: is it possible to obtain a radiation pattern outward
> the screen with some front to back ratio ?
>
> If it is possible could someone point me toward the rigth direction ?
>
> I need to calculate the optimum (in term of gain) supply phase and distance
> for each coco
>
>
> I'm not an antenna engineer and having read the Jasik handbook on this
> topics
> i got lost in angle definition ( teta psi etc...)
>
>
> Thank you
>
> IZ1BLH
>
> Giuseppe Rossi
>

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