Please help! How to do the self-calibration technique for the free-space measurement?

[hippo]

Hi

I'm a newbie. I need to do the free-space measurement but I don't know how to do the self-calibration. I know that I need to do TRL or TRM calibration with some absorber and reflective plate.
However, I'm confused how to do that. Since normally I will go to "Calibration" menu in network analyzer and follow the step. But here I don't know where can I find Thru, Reflect, Match to do the calibration.


Thank you very very much for your help

 

[drkirkby]

Perhaps if you explained yourself a bit better, you might get some help. If you define your terms like "free space measurement", then people might have some hope of helping you. But I for one can't work out what the hell you are asking help for.

 

[hippo]

I'm really sorry about what I wrote.
To clarify my question:
I have to set up measurement using 2 horn antennas and 2 lens, so I can put my sample between and see what is the reflection and transmission. However, i don't know how to do the calibration in this measurement.

Thank you very much

 

[drkirkby]

So are you trying to see the reflections caused by the horn antennas when you place a light source and detector near the lens? Is the lens the sample?

Are using the Buzuka model 3434X TDR?

How about defining your setup carefully.

 

[E Kafeman]

Drkirby, calm down, it is understandable for most RF engineers that hippo is asking for a specific setup!

If you define your terms like "free space measurement", then people might have some hope of helping you.

"Free space measurement" is a defined RF term, describing a condition under which RF field measurements are done.
The problem with "free space" is that it is assumes an ideal reflection-free planar wave condition in absolute vacuum which is hard to fully achieve in a normal RF laboratory, but by doing error correcting calibration of the measurement location environment can a lot of RF-related parameters still be measured relative precise. A good start to understand why "free space" is an important RF term is to learn about isotropic antenna, a basic ideal antenna.

But I for one can't work out what the hell you are asking help for.

"Thru, Reflect, Match" is the same as "Thru, Reflect, Load" (TRL) which are calibration procedures found in most Vector Network Analyzers (VNA) but many alternative procedures are also common. If you not understand this I assume that you not is familiar with a VNA which is a common RF tool. Try some Googling if you not have anything else to add then that you not understand common RF.

Probably do hippo want to do a contact-less permittivity measurement in microwave range. This is done by placing a measurement sample between two communicating antennas and compare how the sample affects what the antennas can "see" relative to known references such as placing absolute absorbing or total reflective material between the antennas.
It can be done by measuring S11 .. S22 for all samples and then do a lot of math but many VNA's have internal functions to make this math.
Hippo is asking for how to perform required VNA measurement calibration as self-calibration in this setup, as a conventional TRL calibration kit not is used. Actual calibration method is described in this document: https://www.adv-radio-sci.net/2/19/2004/ars-2-19-2004.pdf
Each VNA manufacturer do often also have additional information about free space calibration methods.

Edit:
The line "Thru, Reflect, Match" is the same as "Thru, Reflect, Load" is not correct.
"Thru, Reflect, Match" is a similar calibration method as "Thru, Reflect, Load" is maybe better.

 

[hippo]

Thank you very much for both of you, Drkirby and E Kafeman.

Yes, E Kafeman I'm quite new in this field so I have many things to learn...and thank you again for your explanation.

 

[drkirkby]

Drkirby, calm down, it is understandable for most RF engineers that hippo is asking for a specific setup!

But he has not properly defined what he is trying to do. One needs to use a lot of guesswork.

Probably do hippo want to do a contact-less permittivity measurement in microwave range.

But if so, he should say so, not leave it to someone to guess what he is trying to do.

Actual calibration method is described in this document: https://www.adv-radio-sci.net/2/19/2004/ars-2-19-2004.pdf
Each VNA manufacturer do often also have additional information about free space calibration methods.

But he never said what VNA he had, but wants help calibrating it. Would you not agree that is a pretty fundamental bit of information missing?

I can't help feeling he could have explained his situation a lot better. Perhaps then I would have no replied with such a tong in cheek answer.

 

[volker_muehlhaus]

But he has not properly defined what he is trying to do.

For those who are qualified to answer, the question is clear.