Phase of the incident and reflected waves the same place, the voltage amplitude of the maximum voltage amplitude sum Vmax, forming antinodes ; incident and reflected waves in opposite phase relative to the local voltage amplitude is reduced to the minimum voltage amplitude Vmin, the formation of the node . Other amplitude value of each point is between antinodes and the node between . This synthetic wave called a row standing . SWR is the standing wave amplitude of the sound pressure at belly Vmax and the node at the ratio of the amplitude of the sound pressure Vmin . In the standing wave tube , the measured VSWR , the sound absorption material can be obtained reflection coefficient and absorption coefficient .
In radio communication , the antenna impedance mismatch with the feeder or the transmitter antenna impedance mismatch , high-frequency energy will produce reflections folded , and the forward part of the standing wave interference occurs confluence . In order to characterize and measure the VSWR characteristics of the antenna system , that is, the antenna of the forward wave and reflected wave is , it established the ” SWR ” concept ,
SWR = R / r = (1 + K) / (1-K)
Reflection coefficient K = (R-r) / (R + r)
(K is a negative value indicates that the opposite phase )
Wherein R and r is the output impedance and the input impedance. When the two values as the impedance , that is perfectly matched , the reflection coefficient K is equal to 0 , VSWR is 1. This is an ideal situation , in fact, there is always reflected , so that the standing wave ratio is always greater than 1 .
RF system impedance matching. Particular attention to the voltage in Bo Bida to certain requirements, because when you use the broadband frequency range is very wide, standing wave ratio will change with frequency , should make possible a wide range impedance matching .
VSWR is a numerical value that represents the antenna and radio transmitters match. If the SWR is equal to 1 , then the transmitted waves transmitted to the antenna without any reflection , all of the radiation out, this is the ideal situation . If the SWR value greater than 1 , then there is some wave is reflected back and eventually into heat , so that the feeder temperature . The reflected waves at the launch pad output can produce a very high voltage , possibly damaging the transmitters.
Test when the first pair of calibrated vector network , according to the device and the power to set the gain of the output signal vector network size , making the device when the first test port power amplifier output disconnect , measured with the highest value is the input VSWR .
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