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Measurements >> RF Measurements >> S21 normalization calibration
https://designers-guide.org/forum/YaBB.pl?num=1229312772

Message started by vanjer on Dec 14^th, 2008, 7:46pm

Title: S21 normalization calibration
Post by vanjer on Dec 14^th, 2008, 7:46pm

Dear everyone,

sorry for the dumb question, but does anyone know how to do S21 normalization calibration using VNA? it is not a full 2 port calibration, isn't it?

There will be 2 ports used, and the response should be S21, but how to do S21normalization and what is S21 normalization?

thanks for your assistance..

Title: Re: S21 normalization calibration
Post by vanjer on Dec 15^th, 2008, 12:23am

I'm checking the response of a RFID tag loop antenna after being excited by a magnetic signal from a SMA loop as we've discussed previously.

The picture is attached below for a clearer explanation

Here port 1 of the VNA injecting a power output, then amplified by a PA to yield a 20 dBm power output. This RF output will become a magnetic field after go out of the SMA loop connector. The tag antenna is put in between SMA loop 1 and SMA loop 2 of the port 2. This response of the tag antenna under test will be caught by the port 2 by the SMA loop connected. Hence, I want to see the S21 response of this.

I'd like to ask how to do the calibration? Do I have to do a full 2 port calibration? Ultimately the S21 response after being calibrated must be a straight line at the center, then the S21 response will be changed after the tag antenna is put in between.

Title: Re: S21 normalization calibration
Post by pancho_hideboo on Dec 15^th, 2008, 3:40am

vanjer wrote on Dec 14^th, 2008, 7:46pm:

but does anyone know how to do S21 normalization calibration using VNA? it is not a full 2 port calibration, isn't it?
There will be 2 ports used, and the response should be S21, but how to do S21normalization and what is S21 normalization?

Who can understand your question with your above explanation in a start of this topic ?
You have to explain your question correctly and in detail.
This is true for your last post(http://www.designers-guide.org/Forum/YaBB.pl?num=1227954859).

My answers are:
(1) Calibrate VNA without cable in full two port SOLT.
(2) Connect cable1-PA-Loop_SMA1 to port 1.
Connect cable2-Loop_SMA2 to port 2.
(3) Measure S21 without DUT antenna.
This S21 value is reference for measuring antenna(resonator).

Then insert DUT antenna(Resonator) between SMA1 and SMA2. Here you have to keep same position of SMA1 and SMA2 as (3).

In antenna measurement you can only measure relative gain not absolute gain.

Here I assume SMA is electrically very small compared to DUT antenna(resonator) and weak coupling between SMA and DUT.
If these are not satisfied, measurement results could be largely affected by interaction between Loop_SMA and DUT such as double resonance phenomena. BPF can be realized by resonator coupling structure.
See my last answer to your last question.

Title: Re: S21 normalization calibration
Post by vanjer on Dec 15^th, 2008, 4:53pm

Thank you for your answers.

How if we set up the thing (cable1, PA, loop_SMA1, cable2, loop_SMA2, without DUT), then select S21 response from the VNA, then press normalize(through) -> from ADVANTEST 3762AH VNA? Ultimately it will be a quite straight line in the center of the VNA screen. Afterwards, we put the loop antenna DUT in between, hence the straight line graph will change to the thing that we want, which is the relative gain.

What the difference between these two?

Title: Re: S21 normalization calibration
Post by pancho_hideboo on Dec 15^th, 2008, 5:54pm

vanjer wrote on Dec 15^th, 2008, 4:53pm:

How if we set up the thing (cable1, PA, loop_SMA1, cable2, loop_SMA2, without DUT), then select S21 response from the VNA, then press normalize(through) -> from ADVANTEST 3762AH VNA?

I don't know a function detail of normalize in ADVANTEST 3762AH VNA.
But it seems that S21 is normalized over measurement frequency span.
So the following result is quite natural.

vanjer wrote on Dec 15^th, 2008, 4:53pm:

Ultimately it will be a quite straight line in the center of the VNA screen.

vanjer wrote on Dec 15^th, 2008, 4:53pm:

Afterwards, we put the loop antenna DUT in between,
hence the straight line graph will change to the thing that we want, which is the relative gain.
What the difference between these two?

If you use normalize function in ADVANTEST 3762AH VNA, latter results is relative gain.
If you don't use normalize function in ADVANTEST 3762AH VNA, you have to subtract former result from latter to get relative gain.

Title: Re: S21 normalization calibration
Post by vanjer on Dec 15^th, 2008, 11:07pm

OK I got it.

Thank you Mr. Pancho :D