s12 vswr relationship
I have a limiter and I gona to measure its band width.I know that band width is a freaquency range that all desired values are satisfied.I measured some parameters of my limiter.the measured parameters are :insertin loss,return loss and VSWR in both S11 & S21 modes.now i have a question:which VSWR is important?VSWR in S11 or VSWR in S21?
the problem is here that is S11 and S21 ,VSWR do not have any overlaps.i meant i cant find any region in frequency that both VSWR satisfied.
now i'm waiting for your helps
THANKS IN ADVANCE men
Dear friends
I hoped some one of you could help me.Is my question clear?
If ne please tell me to tell that in some more details
Thanks again
Maybe nobody answered because the question is confusing. S11 can be converted into VSWR, but S21 can not. Did you mean to say S22?
the magnitude of S11 and S22 should be about the same and < 0.1, and the magnitudes of S21 and S12 should be nearly 1 for all frequencies in a limiter (at low power levels). If not, you do not have a good limiter design.
Dear biff44
when I review the meaning of VSWR i see that VSWR is the ratio of the maximum and minimum of a voltage.ok?
know imagin that we have a two port network and the incident wave comes from port #1 and goes out from port#2
so maybe some waves reflecte from port 2 because of many reasons,then the existance of VSWR would be possible.I meant although we dont have any inout from port #2 when we are measuring S21 but maybe we have some reflection due to incident signal and mismatch.so the existance of VSWR is possibe while we are measuring S21
young
I tried to understand your explanation, but I didn't, sorry.
Let me tell you what are "classical" S par usage on a 2 port devices:
Input reflection: S11 or VSWR, you would like to minimize it to avoid that the power you inject to your dvice is reflected back.
Forward (Power) Gain : S21
Reverse (Power) Gain: S12
Output reflection: S22 or VSWR, see input.
I hope it can help.
Mazz
Dear mazz
sorry because of my incomplete question.to be accurate I have this problem.I've measured the S paameters ofsome limiter using hp 8510c VNA.while measuring S21 I run in to some VSWR,what is this VSWR.Is that easonable to have such a VSWR?
Sorry young
but still I do not understand: "while measuring S21 I run in to some VSWR" what does it mean?
And what are you looking for?
Mazz
Dear Young,
Please understand that limiters are tested with power sweep. And when you do power sweep the limiter will load low impedance such that the power output is still low. This results in VSWR change.Under limiting operation no one is interested in VSWR but before threshold it should have low IL and good RL
Dear friends
At first thanks for your rplies.second I have to ask that do you guyes work with VNA 8510c?
If yes then we can talk about my problem.I probably bade some mistale when working with VNA and you can help me
HI Young.
Your question is not too clear, and saying VSWR of S21 is incorrect.
S21 on is the Gain of your DUT. S22 is the S-parameter for Output VSWR
But to help out on which VSWR is important:
S11 will be important because it will be connected to some input /signal device, and
you should have a good match between them(Generally) .
S22 is important because a bad match on this side will make the output power low,
change the gain of the output stage of your limitier, and change the frequency response/bandwidth the Amplifier.
Hope this helps.
I've been working with different VNAs, but not with the old (but really good!) 8051.
If you have specific questions, just put here.
Mazz
Dear friends
thanks for your relies.I know some things about microwave and undrestand your explanation about S11 & S22 and S21.by the way thanks for them.After calibrating 8510c with my DUT there is some panel that deal with S parameters.ok?four keys exist.S11,S21,S22& S12.ok?and also there exist some other panel named FORMAT.If you press this key then some parameters appear in the right hand side of the screen.one of this parameters is SWR.this SWR exist in both S11 and S21.and gives you some curve (power versus frequency).I dont underestand the meaning of this VSWR
THANKS AGAIN
Voltage standing wave ratio represents the ratio between the max and min of a standing wave in a transmission line.
It depends from the difference between the characteristic impedance of a transmission line and its termination.
If there is no difference, VSWR=1, otherwise is >1.
It has a math relationship with return loss.
If your device under test has a large gain and small reverse gain, you can see that VSWR depends only from S11, so most probably you do not have to take care about VSWR of S21.
Let me suggest to you to read some book or at least some HP application note on S-parameters.
I hope it can help.
Mazz
dear mazz
you look so cool and thanks for your replies.As i mentined befor my DUT is some limiter and i tried to extrasct its specifications.At some frequency range the insersion loss was so great.some number around 0.7 dB and return loss was almost large(fortunatly).as I told you befor during that test with such result I measured VSWR for S21.and now what is your opinion?
My opinion is: simply forget about VSWR of S21. For me it has no meaning.
Mazz
hi dear mazz
thanks for your opinion.hope to access your ideas later.