Set the type of stepped frequency sweep as Linear or Logarithmic:

Linear: the frequency sweep is linearly incremented by the step size from the start frequency to the stop frequency. The size of each step is set using the STEP SIZE or NUMBER OF POINTS.

Logarithmic: Step size increases logarithmically with frequency and is determined by a logarithmic curve fitted between the sweep start/stop frequencies. The number of steps is set using the NUMBER OF POINTS.