2X-thru

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. 5(c), T11, the impedances of fixtures A and B at the interface of the SMA to the microstrip line are 55.15 and 52.24 Ω, respectively, with a difference of 2.91 Ω. Owing to process instability and errors in circuit fabrication, there are large differences in the S parameters of fixtures A and B, which may lead to inaccurate and unsatisfactory test results. In the actual production process, completely symmetric fixtures A and B could not be fabricated; therefore, errors between them were inevitable. In addition to the unavoidable factors, the 2X-thru structure designed in this study is symmetrical and can provide significant reference data for testing.

s11与s21：对应2X直通结构的先进设计系统（Advanced Design System，ADS）仿真结果，其中引入夹具A与夹具B的S2P文件，以验证两夹具是否对称。由图5(c)中2X直通仿真的插入损耗S21与回波损耗S11可知，夹具A与夹具B的插入损耗基本重合，但回波损耗并未完全一致——这是由于两夹具的传输线在同轴连接器与印制电路板（Printed Circuit Board，PCB）连接处存在阻抗不连续现象。在图5(c)中，T11对应的SMA接头（SubMiniature version A）至微带线接口处，夹具A与夹具B的阻抗分别为55.15Ω与52.24Ω，二者差值为2.91Ω。受电路制作过程中的工艺不稳定性与误差影响，夹具A与夹具B的散射参数（S-parameter）存在较大差异，这可能导致测试结果不准确且效果欠佳。在实际生产流程中，无法制备完全对称的夹具A与夹具B，因此二者之间的误差不可避免。除上述不可控因素外，本研究所设计的2X直通结构具备对称性，可为测试工作提供极具参考价值的数据。