Hi Mel,
> When building a multi element array, I have had to put in odd phase shifts
> to properly achieve the pattern I wanted. Using different lengths of feed
> line works, but is obviously difficult to adjust. Anyone have a good
There are a dozen solutions, but remember these rules. If you use
transmission lines:
A *mismatched* feedline only shifts phase the amount of the length
when the line is an exact electrical multiple of 90 degrees.
Be sure your feedlines are matched or you know the phase shift
with the mismatch. If the line is mismatched and is not a multiple
of 90 degrees, the phase shift is not equal to the line length in
degrees!
Maximum error is when the line is an odd-multiple of 45 degrees,
and of course with the highest mismatch and longest lines.
For example, a 135-degree long RG-8 line teminated in a 1.5:1
resistive mismatch shifts phase 146 degrees.
If you use a hybrid:
A hybrid only shifts phase the design amount when every port is
perfectly matched and only at the design frequency.
and:
There is no passive device available that splits power evenly into
different load impedances.
There is no minimum-loss continuously variable phase system that
does not shift amplitude ratios when the lines are mismatched.
> reference for designing adjustable feedline phase shift networks? I
> vaguely remember an article (many moons ago) on doing so, but could not
> drag it out. Thanks.
You can use conventional T networks to vary phase and power
division, or design the entire system.
You can use a BCD switched line (like a BCD switched set of lines
in series 2, 4, 8, 16, 32 degrees long will give you every two
degrees from zero to 62 degrees) to vary phase but you will have
no control over power division and the phase will only be correct if
the lines are matched. This is the system I use.
There is software that calculates phase shift of networks and
transmission lines with various loads. KM5KG Grant Bingeman
wrote some. I don't know if there is any freeware.
73, Tom W8JI
W8JI@contesting.com
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