Using VNA to test the PCB impedence

Crosstalk caused by discontinuities of transmission lines can seriously affect the quality of signal transmission, which leads to the problem of signal integrity. By introducing the principle of impedance test in vector network analyzer, and comparing the open response calibrated measurement result under Smith chart format, port extension compensated Smith chart format, impedance format and phase format, the paper describes the information stated by these three different formats under frequency domain; Using time transform function of the vector network analyzer to evaluate PCB traces under time domain, that can get the PCB traces impedance and the impedance discontinuity location information. The measurement result of a 3.5mm transmission line explains how to use the vector network analyzer to evaluate the impedance characteristics of PCB traces under both frequency and time domain; this provides a new method of verifying PCB design.