RF Cascade Workbook 2002™ et. al. FAQs |
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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 “PSAT,” 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 PSAT of a stage, then a red “S” is placed in the “!!!” column as an alert to the user. A separate calculation is provided for PSAT to permit the user to keep a tab on power in the system, and to estimate the dynamic range. PSAT, 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. PSAT for each stage is calculated based on PSAT of the previous stage (N-1) and the gain, input power level and PSAT of the current device (N) as follows:
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 PSAT – P[n], and does not include a term for minimum signal-to-noise ratio as is sometimes used. To reiterate, PSAT 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:
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