How to measure S11 and get resonance frequency of RFID tag antenna?

Hi all,

I need help in measuring RFID Tag antenna. I am having some Tags manufactued locally. How to know its resonance frequency. How can I measure S11. Is there any technique by which I can connect tag to network analyzer.

Any related document will help

Thanks in advance

Regards
GV

This are the documents you need
Don't forget to press helped me button
Abhishekabs

Thanks Abhi.

One query
Why we should use a directional couples . Cant I make a one port calibration and directly measure S11.

Further,

In my situation my antenna is a simple loop structure with an embedded microchip having a non 50 ohm impedance. Without the chip antenna impedance is only few ohms. to put my question in one line.

How to measure resonant frequency of an RFID tag ?

Regards
GV

HI, GV
please find the attached paper which will describe how to measure the antenna resonace charastristic.
requirements: Network analyzer
semirigid cable/ coaxial cable
calibration unit for N/A

yaa thanks,

But my issue is
1. I cannot solder cable as its on PET . need to use some probes.
2. Its a non 50 ohm system. chip impedance is R+jX.

regards
GV

hi GV

1. I cannot solder cable as its on PET . need to use some probes.
2. Its a non 50 ohm system. chip impedance is R+jX.

can you more clear on this and send the snapshot of your PCB

kumar

Hi,

Sorry that cannot be done from my work place.

Its not a PCB . RFID tag antenna is made of silver ink or aluminum extrusion over PET of 200 micro meter thickness.


thanks
Vinod

look at this pic how measurement is done.
You need to use directional coupler because you need something as a reference when you are doing measurement.
I woild recommend you to read some basic application notes/manuales by Agilent
on Network analyzer & spectrum analyzer.
They will be helpful.

There are detailed test specicfications for some RFID standards, including the topics you're asking for. Unfortunately you didn't even mention the frequency band of your application.

Thanks Abhishekabs for the pics,

I will do that.
I do not have a directional coupler here, that is why I wanted to know what is the purpose.
what I feel is reflection from antenna will go into the source and may affect the measurement, to avoid that we use a diretional coupler.
what I want to know is , I think there will be a change in power or amplitude ( Y axis) but still I will be able to know correctly the resonant frequency , Is that correct.

I couldn't understand the above line , I will try to go thru some application note and try to understand how and also why a reference is made for s11 measurement,


Sorry FvM,

My frequency band is 950-955 MHz Japanese RFID , ARIB standard.

Please let me know if you know any test specification for RFID , especially for Tag or Antenna measurement , 950-955 Mhz. I have seen test specification in ETSI for European band 865 MHz to 868 MHz . They are on system level and do not speak about how to measure antenna.

ETSI EN 302 208-1 V1.1.2 (2006-07)]
Electromagnetic compatibility and Radio spectrum Matters (ERM);
Radio Frequency Identification Equipment operating in the band 865 MHz to 868 MHz with power levels up to 2 W;
Part 1: Technical requirements and methods of measurement

Thanks and regards
GV

Hi GVVIN
It really difficuilt to do resonance frequency check on analyzer without directional coupler.
see this for your information
http://www.microwaves101.com/encyclo...alcouplers.cfm
Refer this site when you need information about any RF component.

Also I have one suggestion for the measurement.
You can built an oscillator & use this patch antenna as a resonator in circuit
This is the best you can do if you dont have directional coupler for measurement.
see the paper i have attached.
Abhishekabs

As long as you use a network analyzer, you don't need a directional coupler,
because the vector network analyzer already contains directional coupler(s).
Abhishekabs uses a spectrum analyzer with tracking generator, and by the
addition of a directional coupler he made a scalar network analyzer system.
The real challenge will be how to connect the network analyzer to the tag.
You will probably need a balun, as most of tag antennas are balanced structure.
I don't have any idea about making physical contacts with the tag antenna, as
I only do soldering. Not familar with wire bonding or other method.
S. H.

Shwoo is right,
There are scalar network analyzers available where up to 3GHz signal generator is in built.
so you don't need directional coupler
There may be some connector available for tag antennas, you need to check.
Also One more suggestion,
If no connection is at all possible then can you use a coupling line below or on top of your tag?

Thanks Shwoo.... that clarifies.

We both were going on 2 tracks......, me talking abt NA and Abishekh on Spec Ana.


Yaa the real problem is how to connect tag and the very low impedance assosiated with tag antenna.

Thanks Abhishekhabs - Coupled lines...yes that idea is good most of my problems can be adresses..

regards
GV

thats why I suggested you you have to use coupling line structure. I have seen people using this.
Couple 50 Ohm line to your input(feed) of tag.

The respective test standard is ISO/IEC 18047-6, but I don't have it. To measure the tag resonance frequency only, a small coupler coil, connected e. g. to a network analyser in one-port mode should be sufficient to my opinion. By reducing the coil size or increasing the distance, a neglectible coupler de-tuning effect could be verified.

I think that if you want to accurate measure the microchip input impedance , you should use the probe station. The probe vendor will provide the probe calibration kit for the network analyzer calibration.

chip coil impedance is very small , near 0.5 ~ 1 Ohm.

Thanks nccu1990

could you provide me more info on probe, vendor/manufacturer. I searched a lot and those I found was for wafer level probes and were very costly.

Regards
GV

Of course it's nice to measure the chip capacitance. However, the resonance frequency of the assembled tag finally matters. Thus I think, measuring the frequency with a coupler coil (like an extended frequency range grdip dip meter) is the most informative measurement, and rather simple too.

Yes. More of the probe station is expensive.

Probe station vendor has Cascade Microtech , Suss , ...

I think that one method is possible , but no accurate.

You can use the VNA do the full two port calibration.
After that cut two coxial cable be the probe and connect at each VNA port.
Use the port extension function to compensate the electrical length.

Then define the VNA port configuration, let 2 port single end input --> 1 port differential input.

Maybe this method is less costly.