[amsat-bb] Cubesat Antenna Modeling and truth?

[Robert Bruninga]

A big problem on small satellites (cubesats) is how to match
antennas.

Simply connecting a network analyzer, or MFJ antenna analizer or
any other test equpment won't work.  Connecting a cable to the
satelltie model will completely upset the near-field and any
useful measurements.

Especiallly, trying to match a 2 meter antenna to a 4" cubesat!

I wonder if the best way is to simply do the best you can with
EZNEC or other modeling tool, then build a true fidelity model
spaceframe with the fully designed and implemented mathcing
network, but reserve one side of the model to have a
field-strength meter on it connected internally to the actual
TX/RX cable to the antenna.  

Then using long insulated dielectric "tweakers" just tune the
matching circuit for max. (Of coures getting out of the way
after each tweak)..  Also, then comparing the results  with a
similar field strength meter and tuned dipole as a reference at
the same distance.

We tried lots of methods, including building in a directional
coupler and having it report its reflected power via
telemetery... but I think the one above is what I will do next
time.   

When the spacecraft is small, relative to a quarter wave,
everything near the spacecraft and any wires/cables have drastic
impact..

Has anyone had other successes?  Just thinking what we should be
telling these students that are building cubesats.  A 6" whip
for 70cm is not too bad on a 4" cubesat, but 2m is compltely
different...

Bob, WB4APR