BUTTERWORTH BAND REJECT FILTER MATLAB PROGRAM

BUTTERWORTH BAND REJECT FILTER

 

 

alphap=2;    %Passband attenuation in dB

alphas=20;    %stopband attenuation in dB

ws=[.2,.4];    %stopband frequency in radians

wp=[.1,.5];    %Passband frequency in radians

%To find cutoff frequency and order of the filter

[n,wn]=buttord(wp,ws,alphap,alphas);

%system function of filter

[b,a]=butter(n,wn,'stop');

w=0:.01:pi;

[h,ph]=freqz(b,a,w);

m=20*log(abs(h));

an=angle(h);

subplot(2,1,1);

plot(ph/pi,m);

grid;

ylabel('Gain in dB');

xlabel('Normalised frequency');

subplot(2,1,2);

plot(ph/pi,an);

grid;

ylabel('Phase in radians');

xlabel('Normalised frequency');