Charlie
There is no error in your model. The gain of a short-spaced array can be
very good, as you have shown. ZL-Special and W8JK antennas are examples of
proven short-spaced arrays.
Yes, such an array can be built to work as designed. Just be aware of the
challenge it presents:
The problem is practical -- the mutual impedances are very large, and
implementing a feed system that achieves the proper currents and phase
shifts can be a daunting task. That task is even greater if you want a
useful bandwidth. Feeding a two-element array is manageable, but the problem
becomes greater with more elements and pattern switching. The critical
tuning will magnify differences among the elements, which will likely change
the pattern as it is switched in the various directions.
For these reasons, there are relatively few broadcast directional arrays
with spacing less than 1/4-wave, almost none with 1/8-wave spacing -- they
are hard to tune and can be unstable over time and with varying soil
moisture.
Several hams have decided that parasitic arrays are much easier to implement
when limited to short spacing, in exchange for a bit less gain than a phased
array.
73, Gary Breed
K9AY
>Here's a modified 1/8 wave spaced 4-Square for TOPBAND.
>I am surprised that it has over 8dbi gain. Can anyone
>tell me why and if not , then what the error might be.
>Charlie - N1RR
>
>Ground Mounted
>1.832 MHz
>4 wires, feet
>s = 70.75
>1 -s 0 0 -s 0 122 .25"
>1 0 -s 0 0 -s 122 .25"
>1 0 s 0 0 s 122 .25"
>1 s 0 0 s 0 122 .25"
>4 current sources
>i1 = 1
>i23 = 1
>i4 = 1
>p1 = 0
>p23 = -135
>p4 = -270
>Wire 1, end1 i1 p1
>Wire 2, end1 i23 p23
>Wire 3, end1 i23 p23
>Wire 4, end1 i4 p4
--
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