Consider the following dipole:
I want to calculate the s-matrix of this circuit: i think it is \$ b = S a \iff S = \frac{b}{a} = \frac{z_L - 1}{z_L +1}\$ with \$ z_L = \frac{Z_L}{Z_o} \$ But according to @AndyAka's answer the coefficient of reflection doesnt have a conjugate on the characteristic impedance as if they assumed its a real quantity, not a complex one.
EDIT
Here is my approach, so i think the diagram is just an abstracted version of this circuit -correct me if im wrong - :
Finally : \$S = \frac{b}{a} = \frac{V_r}{V_i} = \frac{Z_0}{Z_0 ^*} \cdot \frac{Z_L - Z_0^*}{Z_L + Z_0}\$



