thanks mimomod for your help.
btw, i have another question which i am stuck in how to begin..It is in the attachement.
Qn) what should be the reasonable value which i should choose for 'fp in "step 2"?
I have devise steps below for the approach.Can you help me see if its correct
steps:
1) Required to find the prototype lowpass cutoff frequency for 'fp and 'fs.
*2) Choose a reasonable value for 'fp
3) Obtain alpha1 and alpha2 by substituting 'fp,Wup,wlp values into the four equations
4) Now, we can obtain 'fs since alpha1,alpha2,Wus,wls values are found and given
5) Compute the analog butterworth lowpass prototype specification
6) Design Analog butterworth lowpass filter
7) Perform billinear transformation to obtain digital lowpass butterworth filter
7) Transform digital lowpass to bandstop using the frequency band transformation
thanks
regards
scdoro