On a small river, the water flows downstream, and suddenly the water flows into the small ditch, the water channel narrows, and the impedance becomes large. At this time, if the water flow rate is very fast, that is, the signal frequency is very high, will it splash water? This is reflection. At this time, is the water level at the end of the small ditch also raised, indicating that this produces a positive reflection and the voltage becomes higher!
Then it started to flow again, and suddenly the water flowed into the big river. The river became significantly wider, the impedance was small, and the water level was low, indicating that a negative reflection occurred, and the voltage was low after superposition.