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How does VSWR measure the quality of an antenna?

Published:2019/10/21 18:00:01 Visits:

Voltage standing wave ratio (VSWR) is the most commonly used parameter in RF technology to measure the good match between components. When amateur radio enthusiasts contact, of course first


I would like to measure whether the standing wave ratio of the antenna system is close to 1:1. If it is close to 1:1, it is good. I often hear this question: But what if I can't reach 1,? Station


The Bobby is a few small, is the antenna qualified? Why is there no standing wave watch on the old-fashioned military radio station of size 81?


Calculation of standing wave ratio

Only when the load impedance is exactly matched to the source impedance can the signal be transmitted from the source to the load. If the load and signal source cannot be matched completely, some signals


It is reflected back to the source, producing forward and reverse waves, which combine to form a standing wave. Standing wave ratio (VSWR) refers to the maximum and minimum levels of standing waves


The ratio, its size ranges from 1:1 (exact match) to ∞.

The formula for calculating the standing wave ratio is:

SWR=R/r=(1+K)/(1-K)

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

(K is negative, indicating opposite phase)

In the formula, R and r are the output impedance and the input impedance, respectively.

When the two impedance values are the same, a perfect match is reached, the reflection coefficient K is equal to 0, and the standing wave ratio is 1. This is an ideal situation, in fact there is always reflection, so the standing wave ratio is always


Is greater than 1.


Recording method of standing wave ratio

When we are testing standing waves, we are used to using a number to indicate the size of the standing wave ratio, such as "the antenna has a standing wave ratio of 1.2, which is very well adjusted" or "standing wave."


If the ratio is 2, there must be something wrong. If you are used to reading the technical articles of foreign authors, you will encounter another way of writing: 1.2:1. In fact, both recording methods are


The same is true. For foreigners, using x:1 will make it clear that the standing wave ratio is obtained by means of two numbers. For some people, "standing wave ratio"


The term has revealed that this physical quantity is obtained by comparing two other numbers, so it is more convenient to use a single number.


Acceptable range of standing wave ratio

When the standing wave ratio is equal to 1, it means that the impedance of the feeder and the antenna are completely matched. At this time, the high-frequency energy is completely radiated by the antenna, and there is no reflection loss of energy; when the standing wave ratio is infinite,


It means total reflection, and the energy is not radiated at all. But we can't do 100% load and source impedance matching, there will always be some signals that are inevitably reflected back by the antenna.


Come, so you need to determine a range as a measure of acceptable standing wave ratio. It is not necessary to pursue a standing wave ratio of 1.1 or less, and 1.5 or less is an acceptable range, 96%.


All are launched.


How to measure the standing wave ratio?

Test steps for standing wave ratio:

First: set the frequency

Second: calibration

Third: adjust the top line (because the general standing wave ratio is greater than 1.5 is a problem, so the setting is generally 2 is enough.

Fourth: MARKER reads the value (if it is greater than 1.5, there is a problem, then proceed to the fifth step)

Fifth: Go back to the home page and select the standing wave ratio fault location.

Sixth: Estimate a distance (set in) from the test point to the antenna point and then read the position of the fault location.

The following table is a comparison table of return loss and standing wave ratio:


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