Brendan - you've got the capability to measure
the reflection coefficient - the Impedance Test
Set you've got can be used to measure Input
Impedance numbers that can then be converted into
S-Parameter values (if that's what's needed for
design).

As to characterizing the device - I would build
a quickie little breadboard with the ability
to 'bias-up' the part (including the Drain) and
then terminate the output (AC-wise) with a
50 Ohm term and then measure the input Z (which
can then be converted into an actual S11 value
if need be). You will still have to be careful - this
device will *still* have gain across a wide range
of frequencies (and it may want to oscillate!).

You might need an inductor (RF choke) on the
drain in order to provide DC feed while making
that point isolated for AC - then AC couple (using
a capacitor) into a 50 Ohm load (or one of the
channels of the NA for S21 values!).

Jim


----- Original Message -----
From: "Brendan Moran" <bmoran@MILLENNIUM.CA>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, July 09, 2002 6:12 PM
Subject: Re: [EE]: Directional couplers & T/R test sets


> > It looks to me like you've got a lot of
> > what you need in that "HP 4395A network
> > analyzer".
> >
> > I would take my active device and build a
> > small fixture and simply characterize it
> > using that HP 4395A at my frequency of
> > interest.
>
> Ah, yes, it is that fixture that seems to be the problem
>
> > Does that particular 4395A have any options
> > (like the Impedance Measurement Function
> > and RF Impedance Test Kit)? (I don't own
> > one - I'm looking at it in the HP catalog ...)
>
> It has impedance analyser, spectrum analyser and network analyser modes.
>
> > Oh - I see you have the HP43961A Impedance test
> > set. (Too bad you don't have the S-Parameter
> > Test Set for the 4395A.)
>
> That's what I said.
>
> > With the Impedance Test Set you can get the Z
> > looking into a 'network' (like your pre-amp).
> >
> > Now you need a test set-up to measure Insertion
> > Loss (and Phase change) and come up with gain
> > (or loss) of a network.
> >
> > What are those four ports on the HP 4395A:
> >
> > 1) RF Output
> > 2) R(ef) Input?
> > 3) A and
> > 4) B inputs?
>
> Correct
>
> > I think you are closer than you think to a
> > solution!
>
> I expect I am.  However, this, unfortunately, falls under the "so close,
yet
> so far" range, I think.
>
> I have just been having trouble figuring out how to measure reflection
> coeficients.  Transmission loss is not a big concern to me, since that
one's
> easy to measure with a network analyser.
>
> Thanks again
>
> --Brendan
>

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