% Digital Lowpass Filter Specifications:
wplp=0.2*pi;%                              digital Passband freq in rad
wslp=0.3*pi;%                              digital Stopband freq in rad
Rp=1;       %                              Passband ripple in dB
As=15;      %                              Stopband attenuation in dB
% Analog Prototype Specifications:Inverse mapping for frequencies
T=1;Fs=1/T;   %                            Set T=1
OmegaP=(2/T)*tan(wplp/2);    %             Prewarp Prototype Passband freq
OmegaS=(2/T)*tan(wslp/2);     %            Prewarp Prototype Stopband freq
% Analog Chebyshev Prototype Filter Calculation:
[cs,ds]=afd_chb1(OmegaP,OmegaS,Rp,As);
% **Chebyshev-1 Filter Order=4
% Bilinear transformation:
[blp,alp]=bilinear(cs,ds,Fs);
% Digital Highpass Filter Cutoff frequency:
wphp=0.6*pi;       %                        Passband edge frequency
% LP-to-HP frequency-band reansformation:
alpha=-(cos((wplp+wphp)/2))/(cos((wplp-wphp)/2))
Nz=-[alpha,1];Dz=[1,alpha];
[bhp,ahp]=zmapping(blp,alp,Nz,Dz);
[C,B,A]=dir2cas(bhp,ahp)