This slides set illustrates how nonlinear behavior can show up as “deterministic noise” in S-parameters measurements.

1. Why are
my S-parameters
so noisy?
This slide set illustrates that nonlinear behaviour shows up as
“deterministic noise” in S-parameters measurements.
1

2. S-par measurement #1
FET Vg = -0.6V, Vd = 2.0V, Id = 28mA
500MHz-18GHz (100MHz spacing)
Source @ -20 dBm
S21 (dB)
10/22/08 2
A first S-parameter measurement is performed on a biased FET, from
500MHz to 18 GHz with 100MHz of frequency spacing, applying
-20dBm at source output.
This slide shows the measured S21 parameter in dB as function of
frequency.
The gain of the transistor decreases smoothly from 11.5 dB to 6dB.
2

3. S-par measurement #2
FET Vg = -0.6V, Vd = 2.0V, Id = 28mA
500MHz-18GHz (100MHz spacing)
Source @ -20 dBm
S21 (dB)
2 measurements plot on top of
each other with Source @ 0 dBm
10/22/08 3
A second S-parameter measurement is performed on the same device,
using the same frequency grid, but applying 0dBm at the source
output. The device is in compression for this input level.
This slide shows a comparison of the resulting S21 parameter as
function of frequency for the two measurement.
One can observe a noisier S21 parameter for the second
measurement.
Moreover, a third S-parameter measurement is performed with 0dBm
at Source output. The resulting third S21 parameter is exactly the
same as in case of the second measurement.
Nonlinear behaviour shows up as “deterministic noise” in S-parameter
measurements.
3

4. Conclusions
Nonlinear behaviour
shows up in
S-parameter measurements
as “deterministic noise”
10/22/08 4
4