s11 and s21:hows the ADS simulation of 2X-thru, where the S2P files of fixtures A and B are introduced to observe whether fixtures A and B are symmetric. It can be seen from the insertion loss S21 and return loss S11 of the 2X-thru simulation in Fig. 5(c) that the insertion losses of fixtures A and B almost coincide, but the return loss is not completely coincident because of the discontinuous impedance of the transmission line of fixtures A and B at the connection between the coaxial connector and the PCB. In Fig.