I have been wondering if the antenna element in phased arrays could be a
loop rather than a vertical. My thinking is that the loop has some level of
directivity so phasing two of them should result in better side lobe
suppression compared to a vertical. Is there any merit to this thought?
Specifically, will I see better RDF numbers if I were to use loop elements
in any of the active 8 and 4 circle systems (e.g., DX Engineering, Hi-Z
Antennas, etc.)?
Hi Rudy,
A loop can work in a fixed array, or bi-directional array. My first antenna
allowing me to work JA's through LORAN from Ohio was a long array of loops,
although these were elongated loops. I also had long end-fire arrays of
small inverted delta loops in Cleveland in the 80's, and small active
verticals.
Small loops do not work well when used in things like four squares or 8
circle arrays. A multiple direction array, like a four square or 8-circle,
requires a uniform pattern of uniform phase from each element or cell.
With a small loop, phase flips 180-degrees immediately after crossing the
null. Also, the directivity is generally poor because the small loop has two
very sharp null points though the loop axis, but a broad response everywhere
else. Both of these things actually hurt performance of arrays with loops
that depend on phasing to eliminate side nulls.
Elongated loops are a different story, because (we probably all know)
elongated loops are not really loops in function. They are really phased
verticals, and the horizontal part or component of the conductors is simply
a phasing line. K9AY's, Flags, Pennants, EWE's, and other forms of elongated
loops are really all just phased verticals in function. They have a wider
null and no sudden phase shift at the null, and no null cone at the side or
"loop axis".
The best element for a traditional 8-circle or four square will always be a
simple vertical, and even in a broadside array we would want to avoid small
loops with deep axis nulls. They are OK as cells in an end-fire array, but
not particularly advantageous for pattern unless elongated. I used small
loops as a matter of "construction convenience" as deltas in a long endfire
array, but the deep side null in that array was really created by
out-of-phase cells of deltas and not the sharp null pattern of the
individual delta. It could have just as well been verticals with no loss of
pattern.
73 Tom
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Topband Reflector
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