%例程4－6    帶通橢圓濾波器的幅頻函數
wp1=10;
wp2=20;
Fs=100;
rp=0.5;
rs=50;
wp1=2*pi*wp1;
wp2=2*pi*wp2;
Bw=wp2-wp1;
Wo=sqrt(wp2*wp1);
[z,p,k]=ellipap(7,rp,rs);
[A,B,C,D]=zp2ss(z,p,k);
[At,Bt,Ct,Dt]=lp2bp(A,B,C,D,Wo,Bw);
[At1,Bt1,Ct1,Dt1]=bilinear(At,Bt,Ct,Dt,Fs);
[num,den]=ss2tf(At1,Bt1,Ct1,Dt1);
[H,W]=freqz(num,den);
plot(W*Fs/(2*pi),abs(H));grid;
xlabel('頻率/Hz');
ylabel('幅值');