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Old April 22nd 07, 11:25 AM posted to rec.radio.amateur.antenna
Dave (from the UK) Dave (from the UK) is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 13
Default Where does the far field start on a phased array?

Wimpie wrote:

Hi Dave,


Hi Wim

Whether or not the formula is applicable, depends on many factors as
mentioned in my previous posting.


For a broadside array, the formula holds with same accuracy as for
continuous aperture antennas. In my antenna courses I use the
broadside array approach to derive the 2B^2/lambda formula.


My situation is very odd. As I said at the start, this is not an amateur
antenna.

The array of "antennas" are not designed to work as one nice antennas,
but are an essentially random(ish) collection of radiating centres.
(However, they are all energised from the same signal source). So they
can be considered like a phased array, as they are regularly spaced all
in one long line.

Hence my original diagram

A---A---A---A---A---A---A---A---A---A

accurately describes the situation. Each "A" is an antenna. The
amplitude and phase can be arbitrary.

I do *not* want them to behave as a nice phased array with decent gain
and low side-lobes! Each antennas is radiating an *unwanted* signal. But
the fact remains that the gain could conceivably be high under some
circumstances, which would create interference.

Hence I need to test this.

I would reserve the term "far field distance" for that distance where
the complete radiation pattern does not change with measuring
distance. In that case, the 2B^2/lambda formula is a good rule of
thumb.


In this case, I am interested in any direction. The direction of the
main lobe will be essentially random.

--
Dave (from the UK)

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