[Photo] What is the VSWR of the antenna

The maximum power transmission can only be achieved if the impedance is completely matched. This is more important at high frequencies! Transmitter, transmission cable (feeder), and antenna impedance are all related to power transmission. Standing wave ratio means the matching of feeder and antenna.

When there is no match, a part of the radio wave emitted by the transmitter will be reflected back, and a reflected wave will be generated in the feeder. The reflected wave will reach the transmitter and eventually be consumed as heat. During reception, the received signal is not good due to mismatch.

As shown in the figure below, the forward wave (transmitted wave) and the reflected wave proceed in opposite directions.

The perfect match will not generate reflected waves. In this way, the voltage amplitude at each point in the feeder is constant, as shown in the left part (a) of the figure below. When there is no match, the voltage waveform on the right of the figure below is generated in the feeder The voltage waveform left in the feeder is called a standing wave.

The formula for calculating the S value of the standing wave ratio (SWR) is shown below:

Of course, there are other methods for calculating the standing wave ratio, but the calculation results are the same.

The higher the standing wave ratio, the more the impedance does not match. For amateur players, the standing wave ratio is less than 1.5.

As a final reminder, the quality of the antenna cannot be viewed solely by the standing wave ratio. Now the reason why everyone is so superstitious about the standing wave ratio is very simple, because the standing wave table is cheap and easy to buy. Don't think everything is OK because the antenna's standing wave ratio is very low. It is really fun to study other characteristics of the antenna (such as directivity).

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[Photo] What is the standing wave ratio of an antenna?
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