I am trying to implement a fourth order Butterworth high pass filter under a Sallen-Key topology. Two frequencies, one at the passband and another for the stopband, are set to be at some specific gain/attenuation.
Consulting the Butterworth tables, I was able to design a functioning circuit with two cascaded Sallen-Key networks. The higher frequency (passband side) has no problems and is within my expectation. The problem is with the lower frequency. The filter fails to assign the lower frequency to the set attenuation level.
This is because the Butterworth filter has a linear 80 db/dec since it is a fourth order filter. I am under the impression that the slope cannot be changed. With that, I am confused as to what possible steps I should take to solve the problem.