I think your problem is your bias circuits.
I suppose you are trying to measure S-parameters at a fairly high frequency.
Your inductors are way too big. Such large inductors will have resonances
at very low
frequencies. If you can, do away with inductors in your bias networks all
toghether and use high value
resistors. At the minimum, use much smaller inductances that have resonant
frequencies several times the
frequencies of interest. What you really want is resonances at frequencies
larger than the ft of the transistor.

reguards,
Cliff

wrote in message
...
I'm fooling around, trying to measure the S params of an HXTR-6101,
Low noise npn uWave transistor. The transistor breaks into low freq
oscillations as I increae the base current. I've got it in a stripline
fixture, I made. I'm feeding the base from a supply,thru a 50KOhm, to
a .1uF & 22 uF cap to ground and 47uH coil to the base stripline run.
Same with the collector. How can I stop the low freq oscillations? You
can see a drawing of the stripline he

http://sdeyoreo.tripod.com/id18.html

Thanks.