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Just wanna to counsult for return loss - RF Cafe Forums
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ngks
Post subject: Just wanna to counsult for return loss
Unread
postPosted: Thu May 19, 2005 4:41 am
Dear all,
May i
know what is the meaning of return loss for S11,S12,S21 and S22?
Thanks
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Guest
Post subject:
Unread
postPosted: Thu May 19, 2005 9:16 am
Return loss is only applicable
to S11 and S22, in fact S11 and S22 are return loss. Return loss is
the ratio of reflected power to incident power.
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Jeanalmira
Post subject:
Unread postPosted: Fri May 20,
2005 1:59 am
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General
User avatar
Joined: Tue
Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi :
I agree with the previous reply. S11 is input return loss and S22
is output return loss. That usually calculated in dB.
This input
and output return losses are caused by the impedance mismatch. That's
why matching circuit comes to the picture.
and it's also related
to VSWR (Voltage Standing Wave Ratio).
I hope it helps.
Regards,
Jean
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ngks
Post
subject: am i right?
Unread postPosted: Fri May 20, 2005 5:16 am
Thanks to all,
In order to measure the S-parameter, How
many source should us provided?
Is it two? if yes, means
input source to measurement S11 and S21
Output source is
to measure S22, s12
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Guest
Post subject:
Unread postPosted: Fri May 20, 2005 1:04 pm
Hello,
You
need 2 sources to measure S11, S122 and also the 2 other S-Parameters,
S12, S21.
Each measurement will give you a set of 2 parameters,
with one port terminated (input or output), while a source is connected
to the other one.
The S-Parameters are related to each other
like that:
b1=S11*a1+S12*a2
b2=S22*a2+S21*a1
Where
b1,2 are the reflected waves, a1,2 are the incident waves.
From
these 2 equations you can get the ratios:
S11=b1/a1; a2=0 (Output
port is terminated)
S12=b1/a2; a1=0 (Input port is terminated)
S21=b2/a1; a2=0 (Output port is terminated)
S22=b2/a2; a1=0 (Input
port is terminated)
Hope this helps.
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ngks
Post subject: higher value or lower value for return loss
Unread postPosted: Tue Jun 21, 2005 12:11 am
which return loss
value is more better, higher value or lower value?
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Jeanalmira
Post subject:
Unread postPosted: Tue Jun
21, 2005 12:59 am
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General
User avatar
Joined:
Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi!
For return loss values, the more negative is the better.
For
example :
-15 dB is better than -10dB.
In other words, the
better your matching networks, there will be lesser loss, so the loss
values will be more negative in a sense.
I hope it helps. :D
Regards,
Jean
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Guest
Post
subject:
Unread postPosted: Mon Jun 27, 2005 8:42 am
The
definition of Return Loss is as follows:
-20*log(S11) or S22,
whichever way you're looking.
Therefore, you would want return
loss to be as high as possible.
If you are talking about just changing
S11 to dB (take the minus sign out of the above equation), that is not
technically return loss. For that, you would want it to be as negative
as possible.
It's just terminology, though, so I'm just nitpicking.
Some people get rather upset, however, when you say you have a negative
return loss :)
Hope that helps,
--Dan
Posted 11/12/2012
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