Imagine water flowing through a flexible pipe. Assume that the water is being pumped by a motor and the other end of the pipe is with us. Now the amount of water coming out of the other end can at best be equal to the amount of water sucked by the pump. Now consider there is a mild twist in the pipe. What does this mean to flowing water? Water sees a portion on pipe that is resisting flow and eventually sending back a portion of water coming towards the twist/bend. This is electrical terms can be told "Water faces a high resistance." In other words, until the bend the water was facing very low resistance and all of a sudden, at the bend it begins to face a much higher value of resistance. This mismatch in resistance is causing a portion of water coming in to flow back eventually causing what is known as "reflections" of water. In a nutshell, resistance mismatch on the line( caused by the bend) resulted in reflections and in the process it is worth to note that not all water sucked by the pump is reaching the other end.
Let us now migrate to transmission line parlance and connect the above scenario with that world. Energy sent down the transmission line is guaranteed to reach the other end "maximum" only when there is no change in the impedance as seen through out the line. When there is a impedance change on the line, there is said to be an impedance mismatch. And when there is an impedance mismatch, RF energy is partially or completely reflected back. A way to quantify these reflections is Standing wave ratio. Reflected waves interact with incident-forward travelling waves to form what is known as standing wave in which the positions of maximum and minimum are constant. For a symmetrical wave sent down, the ratio of maximum and minimum should be the same in magnitude. This ratio of maximum to minimum is called as standing wave ratio. Lower the standing wave ratio, better is the matching and higher is the power delivered. Higher the standing wave ratio, worse is the matching, higher are the reflections and lesser is the power delivered.
Let us now migrate to transmission line parlance and connect the above scenario with that world. Energy sent down the transmission line is guaranteed to reach the other end "maximum" only when there is no change in the impedance as seen through out the line. When there is a impedance change on the line, there is said to be an impedance mismatch. And when there is an impedance mismatch, RF energy is partially or completely reflected back. A way to quantify these reflections is Standing wave ratio. Reflected waves interact with incident-forward travelling waves to form what is known as standing wave in which the positions of maximum and minimum are constant. For a symmetrical wave sent down, the ratio of maximum and minimum should be the same in magnitude. This ratio of maximum to minimum is called as standing wave ratio. Lower the standing wave ratio, better is the matching and higher is the power delivered. Higher the standing wave ratio, worse is the matching, higher are the reflections and lesser is the power delivered.
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