Among electrical issues to consider
when choosing antenna system VSWR or return loss is also important. VSWR is the
measure of the impedance matching between the antenna element and the medium
into which waves are transmitted. Difference in impedance causes reflection
resulting in Voltage Standing Waves. VSWR is the relation between maximum and
minimum of the standing wave. VSWR= 1 means
that impedance matching is perfect. However this can not be achieved in
practice. It is an ideal case. VSWR can also be taken as measure of return loss
of the Antenna.
VSWR:
Reflected Power/ Transmitted Power.
Return Loss: 20 log ( VSWR+1) /
(VSWR-1).
In
Base Station antenna it is desirable to have low value of VSWR, normally upto
1.3, as low VSWR means high quality. Selection of antenna is a trade off
between required gain and value of VSWR i.e. to achieve low VSWR antenna gain
will have to be sacrificed to certain extent.
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