Standing Poppy

　　At the point where the phase of the incident wave and the reflected wave is the same, the sum of the voltage amplitudes is the maximum voltage amplitude Vmax, forming a wave belly; At the point where the phase of the incident wave and the reflected wave is opposite, the voltage amplitude is subtracted to obtain the minimum voltage amplitude Vmin, forming a node. The amplitude values of other points are between the antinodes and nodes. This type of synthesized wave is called a standing wave. The standing wave ratio is the ratio of the amplitude Vmax of the sound pressure at the antinodes of the standing wave to the amplitude Vmin of the sound pressure at the nodes. In the standing wave tube method, by measuring the standing wave ratio, the sound reflection coefficient and absorption coefficient of the sound-absorbing material can be calculated.

　　In wireless communication, if the impedance of the antenna does not match the impedance of the feeder or the impedance of the antenna does not match the impedance of the transmitter, high-frequency energy will reflect back and merge with the forward interference to form a standing wave. In order to characterize and measure the standing wave characteristics in antenna systems, that is, the situation of forward waves and reflected waves in antennas, the concept of "standing wave ratio" has been established,

　　SWR=R/r=(1+K)/(1-K)

　　Reflection coefficient K=(R-r)/(R+r)

　　(When K is negative, it indicates opposite phase)

　　In the equation, R and r are the output impedance and input impedance, respectively. When two impedance values are the same, perfect matching is achieved, with a reflection coefficient K equal to 0 and a standing wave ratio of 1. This is an ideal situation where there is always reflection, so the standing wave ratio is always greater than 1.

　　Impedance matching of RF system. Special attention should be paid to ensuring that the voltage standing wave ratio meets certain requirements, as the frequency range is wide in broadband applications and the standing wave ratio will vary with frequency. Impedance should be matched as much as possible within a wide range.

　　The meaning of standing wave ratio:

　　Standing wave ratio is a numerical value used to indicate whether the antenna and radio transmitter are compatible. If the value of SWR is equal to 1, it means that the radio waves transmitted to the antenna are not reflected and are all emitted, which is the most ideal situation. If the SWR value is greater than 1, it means that some of the radio waves are reflected back and eventually become heat, causing the feeder to heat up. The reflected radio waves can also generate a considerable voltage at the output port of the transmitter, which may damage the transmitter

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