How to implement Bessel filter transfer function for bandlimited electronic driver after pulse shaping? (number of poles 4 and B-3db equal to 7 GHz)

clc;

clear all;

close all;

M=2;

N_bits=1e5;

SPS=8;

f0 = 193.4e12;

k = log2(M); % Number of bits per symbol

Nsymbol=N_bits/k; %Number of Symbols

data=randi([0 M-1], N_bits,1);%%

moddata=pammod(data,M)+1;%%2PAM MODULATION

%Upsampling

signal=zeros(1,SPS*Nsymbol,1);% makes a vector of zeros with the size of sps*Nsymbol

signal(1:SPS:end)=moddata;

%%Pulse shaping

A=1;

B=ones(1,SPS);% makes a vector of ones with size of sps [1,1,1,1,1,1,1,1]

Z=filter(B,A,signal);

%Elecrotnic Driver modeled as Bessel filter transfer function

Poles=4;

Bandwith=7*1e9;

% for Counter=1:length(Bandwith)

WC=2*pi*Bandwith;%(Counter); %%Angular frequency

[b1,a1]=besself(Poles,WC);

%s=1j*2*pi*f;

%H=polyval(b,s)./polyval(a,s);

%TF=H/max(H);

% plot(f,abs(TF).^2)

%grid on

[bz, az] = impinvar(b1,a1,Bandwith);

y=filter(bz,az,Z);

%y=real(ifft(fftshift(TF).*(fft(Z))));

% end;