I have experimented (successfully) with two sets of loops spaced 1/4-wave.
They were wired to be in phase when broadside, and 180 deg. (phase
reversed) when in endfire mode. Endfire could be improved with different
phasing, but the 0/180 setup is very simple.
When broadside, the main lobe is narrowed somewhat, with better S/N but
not a big difference to the ears.
The difference in directivity is less than 1 dB. The additional side null
depth is less than 3 dB.
Endfire, you get the same F/B as a single loop, but add two very deep
nulls off the sides. Since the null is also overhead, the array now
rejects high angles. The pattern improvement is quite dramatic in many
cases.
There are two ways to fire end-fire. If you use a phase around +110 or -110
with 1/4 wave spacing, you will enhance back null with little side null
change. If this is made crossfire it can be made to work on multiple bands
but will have a side null change with bands. If you flip 180 and feed, it
adds deep side nulls and will also add additional nulls on higher bands.
The only real noticeable change would be some form of endfire, either the
180 to improve sides or the more complex unidirectional to improve rear null
depth.
73 Tom
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