On 1/31/19 5:51 AM, Bob kb8tq wrote:
Hi
If you take a hammer to one of these antennas, they seem to mostly play games
with transmission lines on pc boards. The number of components involved is
pretty
small.
If hammering one apart does not sound like a great thing to do, there are
pictures
here and there. I have yet to see a picture that shows enough to actually make
sense
out of. I’d bet that is intentional.
Looking at network analyzer sweeps, it becomes pretty apparent that whatever
combination of things are involved, they only work inside each of the target
sub-bands.
Once you get to the edge, it all falls apart. It comes back together once you
get to
the edge of the next sub-band. Some of that is intentional filtering so sorting
it out
that way … not so much.
Bob
These things are designed by someone sitting down with HFSS or similar,
starting with a cookbook layout and iterating the design manually until
it works. It's faster than xacto-knife, copper foil tape, etc.
You can literally click and drag and watch the S11 change in real time
if you've got enough CPU horsepower.
Someone who is reasonably facile with the tools (and has a design to
start with) can probably knock one out in a day or two of work.
Then a week to get the prototype back from fab and you test it, and call
it done.
I'll bet they don't agonize too much about axial ratio off boresight or
perfect phase center vs look angle.. It's more about "is the degradation
tolerable for the desired application".
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