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Voltage standing wave ratio (VSWR) (pronounced "vizwar" [1] [2]) is the ratio of maximum to minimum voltage on a transmission line . For example, a VSWR of 1.2 means a peak voltage 1.2 times the minimum voltage along that line, if the line is at least one half wavelength long.
Increasing return loss corresponds to lower SWR. Return loss is a measure of how well devices or lines are matched. A match is good if the return loss is high. A high return loss is desirable and results in a lower insertion loss. From a certain perspective 'Return Loss' is a misnomer. The usual function of a transmission line is to convey ...
For example, the SWR bandwidth is typically determined by measuring the frequency range where the SWR is less than 2:1 . Another frequently used value for determining bandwidth for resonant antennas is the −3 dB return loss value, since loss due to SWR is −10·log 10 (2÷1) = −3.01000 dB.
The voltage standing wave ratio (VSWR) at a port, represented by the lower case 's', is a similar measure of port match to return loss but is a scalar linear quantity, the ratio of the standing wave maximum voltage to the standing wave minimum voltage.
Examples of estimated bandwidth of different antennas according to the schedule VSWR and return loss by the help of the ANSYS HFSS [1]. Ansys HFSS (high-frequency structure simulator) is a commercial finite element method solver for electromagnetic (EM) structures from Ansys.
In real systems, relatively little loss is due to mismatch loss and is often on the order of 1dB [dubious – discuss]. According to Walter Maxwell [2] mismatch does not result in any loss ("wasted" signal), except through the transmission line. This is because the signal reflected from the load is transmitted back to the source, where it is re ...
A standing wave ratio meter, SWR meter, ISWR meter (current "I" SWR), or VSWR meter (voltage SWR) measures the standing wave ratio (SWR) in a transmission line. [ a ] The meter indirectly measures the degree of mismatch between a transmission line and its load (usually an antenna ).
The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR). Antennas which are not a significant fraction of a wavelength in size are inevitably inefficient due to their small radiation resistance.