calculate the reflection coefficient using MATLAB program

Hi, evryone
I wrote a program using MATLAB to calculate the reflection coefficient, but the value of the RC is 3.8282. so the program is incorrect. Could you check it for me? Thank you in advance! The program is below.
clc
clear
epsilon=[10.98+6.96j 14.36+11.15j 7.89+3.63j 2.91+0.113j]; %relative permittivity
h=[5.1 8 3.56 3.66]; %thickness of layers
z0=377; %the free-space impedance
f=6*10^9; %frequency of EM
c=2.9979*10^8; %the light speed

for a=1:4
eta(a)=z0./sqrt(epsilon(a)); %the EM intrinsic wave impedence
k(a)=(2*pi*f*h(a)*sqrt(epsilon(a))./c)*1i; %the complex wave number
end

z(1)=(eta(1)*tan(k(1)))*1i;
for a=2:4
z(a)=eta(a)*((z(a-1)+(eta(a)*tan(k(a)))*1i)./(eta(a)+(z(a-1)*tan(k(a)))*1i));
end
RC=abs((z(4)-z0)./(z(4)+z0)) %the reflection efficient