Why do I receive different results when I set the maximum FIR filter length to a number that is not a power of 2 in RF Blockset?

I created a model that uses the General Passive Network block and specified, in the RF Inport block, a finite impulse response filter length of 129. The simulation results are different when the finite impulse response filter length is set to a power of 2.

Answer 1

[MathWorks Support Team]

This enhancement has been incorporated in Release 2008a (R2008a). For previous product releases, read below for any possible workarounds:

This is due to the modeling technique used in the RF Blockset. When the finite impulse response is truncated to the length specified by the user, the effect of the truncation is similar to windowing with a rectangular window. As with any windowing technique there will be an effect on the truncated signal spectrum. The difference between the results in the 129 case and in the 128 case illustrates the effect of a windowed filter response.