The reflection of the signal is directly related to the sudden change of the impedance of the line. Part of the signal power (voltage and current) is transmitted to the line and reaches the load, but part of it is reflected. The impedance mismatch between the source end and the load end will cause reflection on the line. It is assumed that the signal transmission process passes through two different areas , the impedance of zone 1 is Z1, and the impedance of zone 2 is Z2. When Z2<Z1, the reflection coefficient is negative, resulting in negative reflection; when Z2>Z1, the reflection coefficient is positive, resulting in positive reflection. The signal bounces back and forth to create oscillations, which cause signal distortion.