Frequency sweep parameters START and STOP can be set with variable declarations in the schematic, but the SCH assignments cannot be edited in the sweep dialog box.
For an S-Parameter simulation the START and STOP frequencies can be equated to a variable that is defined in an equation if the variable name is entered in the schematic (“Start=Fmin”), and all works as expected. But when the S-Parameters properties dialog is opened an error occurs (“Step: 0 Fmin”). Attempting to edit the step value causes the number of points to be calculated as a negative number.