Hi Kuan,
The symmetrize is used at the end of the function to ensure the individual s parameter of the network are symmetric.
For a 2 – port symmetric reciprocal network, the conditions s12 = s21 and s11 = s22 holds
This is due to the reciprocal nature of the network, which ensures that the ABCD parameters satisfy
(AD - BC = 1), leading to ( s12 = s21). The symmetric network condition requires (A = D ) in the ABCD parameters, which makes the numerators of s11 and s22 identical, as defined below:
s11 = (A + B./z0 - C.*z0 - D)/den
s22 = (-A + B./z0 - C.*z0 + D)/den
This ensures the s11 = s22 and s21= s12 for a 2-port network.
In case of 3 transmission line the reciprocal network ensures sij = sji so s21 = s12 follows. However, the parameters s12 and s32 are independent and do not necessarily equal each other.
Kindly refer to the below documentation of “rlgc2s” for more details:
I hope this helps!
