Richard
I looked thru The ARRL antenna book and I cannot find
any antenna let alone the two element phased array
that showed ZERO radiation to the rear of the feed point.
Is it possible you are pointing to F/B for minimum radiation
where I am refering to zero front to rear:
Regards
Art

"Richard Harrison" wrote in message
...
Art Unwin wrote:
"I have just come to realise that if one drew a polygon of element
phases in an array and all elements were 180 degrees to its companion
element and excluding the driven elemment, the max gain and max front to
back will occur at the same frequency!"

Would an antenna made entirely of pairs of identical out of phase
elements be a good antenna?

A "polygon of element phases" must refer to the resultant current in
each element and their combined effect at a point (P) for example in
the far field. Art must have resolved and composed vectors or phasors at
some time. The resultant of any number of vectors can all add to zero or
to some other number and direction. A zero sum often happens in physics
when systems are in equiblirium. Newton said that any action results in
an equal and opposite reaction. Application of a new force often causes
no loss in equilibrium, just a corresponding added reaction.

The reflected wave from an antenna may change in magnitude in proportion
to an incidebt wave yet be nearly exactly equal in magnitude and
180-degrees out of phase with the incident wave, if the reflection is
perfect.

A polygon is a closed plane bounded by straight sides. It can represenht
forces.

Art asked if there were anything written about complete front to back
cancellation in two radiators carrying oppositely directed signals if I
understood the question. Indeed Kraus of W8JK fame has a lot to say
about the possibility.

Kraus writes about an "Array of Two Driven 1/2-wavelength El;ements.
General Case with Equal Currents of Any Phase Relation." in his 1950
edition of "Antennas".

It includes on page 294, field patterns for physical spacings and feed
phasings. For example, at a spacing of 1/8-wavelength and a phasing of
135-degrees, there is complete cancellation in one direction while there
is maximum radiation in the opposite direction.
That`s the good news. Now the bad.

On page 297 Kraus says:
"However, in the flat-top (an advantage placing all elements at maximum
height) antenna such losses may have considerable effect on the gain (as
the feedpoint resistance is very low). Therefore, the question of losses
and of radiating efficiency will be treated in this section in
connection with a discussion of arrays of two closely spaced,
out-of-phase elements. The term "closely-spaced" will be taken to mean
that the elements are spaced 1/4 wavelength or less."

Then, Kraus shows another fly in the ointment on page 300:

"Hence the Q for 1/8 wavelength spacing is about four times the Q for
1/4 wavelength spacing. Very large Q indicates a large amount of stored
energy near the antenna in proportion to the energy radiated per cycle.
This also means that the antenna acts like a sharply tuned circuit."

So much for bandwidth!



Best regards, Richard Harrison, KB5WZI