RF Cafe Software

RF Cascade Workbook

About RF Cafe

Copyright

1996 -
2016

Webmaster:

Kirt Blattenberger,

BSEE
- KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

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Q. Why won't the VSWR checkbox, row hide/show, and other special functions work?

A. Macros must be enabled for the functions to work. To enable macros, go to the "Tools/Macros/Security..." menu selections. Choose either the Medium or Low security option. Close the workbook and then re-open it. If you selected Medium security, a window will open during loading that asks if you want to enable macros - select Enable. If you selected Low security, the workbook will load without prompting you.

Q. How is dynamic range calculated versus linear gain , noise figure, noise power, etc?

A. Both the “Gain” and “P[sig]” columns are calculated based on a linear small signal model and assume no power limitations.
Similarly, all other parameters except “P_{SAT},” and “DR” are based on linear models, since the standard cascade
formulas are set up that way. Operation into the nonlinear region negates the formulas. However, if a situation exists whereby
the output power would exceed the P_{SAT} of a stage, then a red “S” is placed in the “!!!” column as an alert to
the user.

A separate calculation is provided for P_{SAT} to permit the user to keep a tab on power in the system, and to
estimate the dynamic range. P_{SAT}, as implemented in this spreadsheet, is a step transition from the linear region
to saturated output power, since attempting to accurately model the transition region is beyond the capability of a simple
spreadsheet. P_{SAT} for each stage is calculated based on P_{SAT} of the previous stage (N-1) and the gain,
input power level and P_{SAT} of the current device (N) as follows:

- Calculate what the output power would be for the current stage using the calculated P
_{SAT}of the previous stage and the gain of the current device (ignoring actual P_{SAT}of the current device).

- If P’<= P
_{SAT}for the current device then P_{SAT}for the current stage is set to P’. - If P’ > P
_{SAT}for the current device, P_{SAT}for the current stage is set to P_{SAT}for the current device.

Noise power (P[n]) of each stage is calculated based on the noise power bandwidth of the device, the cumulative linear gain through the current stage, and the cumulative system NF through the current stage as follows:

Dynamic range for each stage is calculated as P_{SAT} – P[n], and does not include a term for minimum signal-to-noise
ratio as is sometimes used.

To reiterate, P_{SAT} is a subjective number whose optimal value is determined by the user. Its function is to
provide an indication of operation – advertently or inadvertently – in the nonlinear range of the components, and to provide
an estimate of the dynamic range that can be expected. More powerful non-linear simulators such as Agilent’s “ADS,” Eagleware,
or AWR’s “Microwave Office” are required to obtain more exact results.

The DR Min/Max cells use the following equations, in keeping with the plan of using the worst possible combination of parameters:

- DR
_{MAX}= P[sat]_{MAX}– P[noise]_{MIN} - DR
_{MIN}= P[sat]_{MIN}– P[noise]_{MAX}