Hi Hwang ming chen,
I have been using he s2tf function for my projects related to control signals. The s2tf function in MATLAB converts the scattering parameters (S-parameters) of a 2-port network into a voltage transfer function. The input to this function typically includes the S-parameters of the network and the source and load impedances, but you can also use it with only the scattering parameters. The input signal for the s2tf function is typically the S-parameters of the network, which are complex numbers representing the reflection and transmission characteristics of the network. The output is the voltage transfer function. It represents how the input voltage is transformed into the output voltage through the network. This can be used for further analysis in control systems, signal processing, or RF circuit design. The output is complex because it has to show both the magnitude and the phase information of the signal. For a better understanding you can refer to this diagram of this circuit which encapsulates the working of the s2tf function:
I used this sample code to understand the working of the function:
S = [0.1 + 0.2i, 0.3 + 0.1i; 0.4 + 0.2i, 0.5 + 0.6i]; % Example S-parameters with complex values
tf = s2tf(S);
disp(tf);
The output is a complex number as follows, which can be converted to polar form to obtain the phase and magnitude:
0.4000 + 0.2000i
Also, for further information, you can refer to the following documentation link for s2tf:
