R3267 Series Spectrum Analyzer Operation Manual (Vol.1)
A.3 Glossary
A-14
Figure A-7 Spurious Response
VSWR (Voltage Standing Wave Ratio)
This shows the state of impedance matching when a spectrum analyzer is connected to a voltage source
whose output impedance is ideal and nominal. The VSWR is expressed as the ratio of the maximum value to
minimum value of a standing wave which consists of traveling and reflected waves. The VSWR is another
expression of the reflection coefficient or return loss.
Referring to Figure A-8, The signal at the receiving end E
1
is the same as the signal at the transmitting end
(E
0
, or the spectrum analyzer input section) if the impedance of the receiving end is matched to that of the
transmitting end.
The reflection coefficient is expressed in the formula shown below when the reflected wave E
R
exists due to
a mismatch between the impedances.
Reflection coefficient m = Reflected wave E
R
/Traveling wave E
0
The Return loss is expressed in the formula shown below.
Return loss = 20 log E
R
/ E
0
[dB] VSWR
= (E
0
+ E
R
) / (E
0
- E
R
)
The relationship of VSWR with the reflection coefficient is as follows.
VSWR = (1 + | m | ) / (1 - | m | )
The range of VSWR is between 1 and
∞
the nearer to 1 this value is, the better the state of impedance match-
ing is.
Figure A-8 V.S.W.R
Traveling wave
E
1
Receiver
Sender§ E
0
Spectrum analyzer
Reflected wave
Signal to be measured
