Specifications

17
Figure B-2 shows the typical display for the entry point
to this interactive model. Figures B-3, B-4 and B-5 show
simulated results for the uncertainty calculator. There
are a number of graphs that can be plotted. These figures
show examples of RSS uncertainty with respect to
instrument match, DUT input match and instrument noise
figure, respectively. This interactive uncertainty calculator
and the spreadsheet version shown in Figure B-1 can be
accessed via the Internet by using the URL on the back
page of this application note.
Figure B-2
Figure B-3
Appendix B:
Total uncertainty calculations
The error model in the spreadsheet shown in Figure B-1
is obtained from the derivative of the Cascade equation
(F1 = F12 - [(F2-1) / G1]). It takes into account the
individual mismatch uncertainty calculations at each
reference or incident plane of the DUT, noise source and
measurement system. This example represents the total
noise figure measurement uncertainty, RSS analysis, for
a microwave transistor with an S11 of 0.5, S22 of 0.8 and
S21 of 5 (14dB). Noise figure uncertainty, here is
calculated as ±0.48 dB. The uncertainty dramatically
improves to ±0.26dB, in this instance, if the gain is
improved to 20dB. The calculation for this error model
is derived in Reference 6.
Figure B-1