Cascade analysis
Updated July 8,
2011
Click
here to go to our page on noise figure (includes a gain/NF cascade
example)
Click
here to go to our calculator page to check out our threestage
cascade calculator
Do to lack of demand and the
pain associated with collecting small money from cheap microwave
engineers, we've stopped trying to sell the Cascade Analysis Excel
workbook way back in 2006. If you ask nicely, maybe we'll give you
the full version for free!
Here's a clickable outline for
this page:
What is cascade
analysis?
Small signal
cascade analysis
Cascaded noise
figure analysis
Large signal
cascade analysis
What is cascade
analysis?
Cascade analysis is a simple
yet powerful tool for analyzing system performance. You can analyze
smallsignal gain and noise figure nearly exactly, and come pretty
close to modeling largesignal performance, such as predicting onedB
compression point.
Everyone and their little brother
has created an Excel spreadsheet for performing Cascade analysis.
The noise figure equation is fairly simple. Adding a decent nonlinear
equation for largesignal performance is a lot more complicated.
But here at Microwaves101, we have already done that and much more
for you in a convenient analysis tool!
Smallsignal
analysis
Under ideal small signal conditions,
gains and losses of cascaded components merely add up in decibels.
However, in real life you will have have the added effects of mismatch
losses and sneak paths. Cascade analysis doe nothing to address
these errors. Be sure to chose components that are well matched
in impedance and you won't have to worry about this.
Noise figure
analysis
Noise figure of a cascade follows
the wellknown Friis equations:
You can learn more on our
noise figure page, which goes through the math on an example
receiver. Meet Harald Friis
in our Microwave Hall of Fame!
Largesignal
analysis
Large signal analysis that can
be done in a simple spreadsheet includes compression point and saturated
power calculations.
The graph below illustrates three
input/output power response curves. The "linear" curve
simply assumes that the output power in dB will be higher than the
input signal by a constant (the gain, 18 dB in the plot). In the
"cubic" relationship, the compression characteristic has
been fit from smallsignal up to saturation with a cubic polynomial.
This works great, until you oversaturate your component and the
calculated gain starts to decrease. In real life the output power
will most likely saturate for all further increases in power. We
call this the "saturated cubic" model. This is what we
use in our cascade analysis tool. Note that this type of curve should
not be applied to squarelaw devices such as frequency doublers
and detectors.
The Unknown Editor burned some
midnight oil and prepared the best known cascade analysis tool ever,
so you will never have to. We call it Cascade101.xls. We are offering
a free version you can download today, and the full version you
can purchase. Both versions have the following features:
 Predict gain, noise figure,
P1dB, Psat.
 Predict Pout for any Pin (each
stage and entire chain).
 Small file size, many copies
fit on one floppy.
 Printer and eyesightfriendly
sheets!
 All computational cells are
annoyingly locked!
Here are the extra features you
will receive when you place an order for the full tool:
