RFID tag measurements

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itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

11 Jun 2008 0:19 RFID tag measurements

Hello to all!!

What is the best method for measuring RFID passive tags for UHF?
The tags don't include the chips.

How should I measure a back-scattering from an RFID tag (without the chip)?

The measurements should be in tne physical layer. (EM wave scattering)

Smile

I.H

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

11 Jun 2008 2:32 Re: RFID tag measurements

Hi

The Micro chip impedance is not 50 Ohms right, So the antenna is matched to some R +JX ohms.

for measurement you can use a RF probe (Wafer probe) and connect to network analyser and verify the impedance at the chip position (without chip). It should be the conjugate of the chip input impedance.

You cannot measure backscatter without the Chip.

Me too working on similar lines.. Have you done simulation of the same ??

regards
GV

itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

11 Jun 2008 10:18 Re: RFID tag measurements

Hi GV!

Yes I did some simualtions with the aid of the CST application note (attached)

Can you send me some information/application note for matching the tag with wafer?
How you can make this measurement if the RFID tag has balanced input terminal?
(The Alien tag for example).

What about attaching a led to its terminal and by radiating on it, it will be "turned on" so we can think that the tag is back scattering (after its matched)?

I read also an article for measuring the response of the tag using two antennas (horn type) what do you think about this setup?
Can we perfrom it, still, without the chip (but with the matching network)?

Thanks for reply,

IH

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GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

12 Jun 2008 3:40 Re: RFID tag measurements

Hi,

I was doing some simulation in CST for Tag antenna design for near field. (H fields). My chip impedance is 48-J148 ohms, As shown in the document you attached I am connecting a Port of 48 ohms and a Capacitor in series for the chip impedance for the simulation. for measurement I am monitoring surface current , E and H fields. Also I am using another antenna and measuring the coupling.

Still I don't think you will get a backscatter signal without the chip, The chip is an active device which helps in retransmission (backscatter) of signal from Tag to reader. Also the RF signal wont be able to drive an Led , even if you convert to Dc the current wont be sufficient to drive an LED , so using LED is not possible. see below link for back scatter
http://www.rfidtribe.com/home/index.php?option=com_content&task=view&id=423

Hope you are working of UHF RFID tag, Are you looking for near field (application near metals &liquids)or far field?, matching You can do stripline type matching.
Find attached the monza chip datasheet. page numbers 12 to 15 explains the different configurations and the impedance for each case is given in page 15. If its a differential configuration , see fig 3-11 connection is made between the RF ports and ground is left free.

Regards
GV

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itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

13 Jun 2008 0:15 Re: RFID tag measurements

Hi GVVN !

As I understood from you, the RFID tag chip doen't contain any "matching network" (resistor and capicator) and you will need to match the chip to the RFID tag antenna.

You said:

Quote:

My chip impedance is 48-J148 ohms, As shown in the document you attached I am connecting a Port of 48 ohms and a Capacitor in series for the chip impedance for the simulation

I don't think this solve the matching issue for the chip.
You'll need to match the chip to his RFID antenna. Hence you be needing to find to antenna complex impedance (R+jX) and to match it to the RFID chip impedance (48-j148).

I work with UHF tags for near field application.

Please advise me about microstrip/stripline matching.
How you actually demodulate the backscatter signal from the RFID tag (RFID -> reader link)?

IH

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

13 Jun 2008 4:03 Re: RFID tag measurements

Hi,

Yes , The chip is a tranceiver by itself and its impedance is not 50 ohms ,it has some R + J ohms , we need to match antenna to this. Normally Lumped elements cannot be used in tags due to physical constrains and manufacturability

Yes port in series with capacitor wont solve matching. This is only for simulation of antenna, to compensate for non 50 ohms impedance of Tag chip. Matching we have to do.

For near field Loop antenna or a varient of that or loop together with dipole is normally used. Loop gives Good H field.
matching - Stub matching you have to do, you cant incorporate lumped elements Cap and Ind in normal Tags.

Regards
GV

itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

15 Jun 2008 0:21 Re: RFID tag measurements

Hello again GV!

About the matching with non lumped/discrete elements, this could be done as a part of the antenna printed striplines. Is this correct?

Second, what about analyzing the backscattering signal from tag to reader?
Is it possible to implantat the antenna reader + its demodulation and encoding for the "tag to reader link" by yourself or we need the reader antenna?
Can you recommend me for some reader to UHF with the latest protocol.
Does "Monza tag" has readers antennas as well?

The tags (and reader as well) need to be in UHF bands, hence the HF tags (13.56MHz) which much suitable for near field application and less prone to metals and near objects reflections should not be taken into account.

About the ability to measure the backscattering of the RFID tag withoutr the chip,
by connecting horn antenna (having G=10 dBi @~920MHz, for example) to port 1 of VNA and the other port (2) to an RFID tag (alone with balun for balanced RFID tag), and see the coupling between them in various distance and etc.
This could test the functionality of the RFID tag and the response when "reading" takes place.
Of course the ability of the RFID tag to backscatter with the chip's information and with the "self excited" mechanism could not be perfrom without the chip.

What do you think?

Thanks,
IH

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

15 Jun 2008 12:05 Re: RFID tag measurements

Hi IH,
yes correct, We have to do with pattern (Striplines).

measuring back scatter . There are certain link equations by which we verify how much power will be received back theoretically.
yes some readers do give RSSI from Tag and we can use the same to measure Back scatter. Monza tag is from inpinj and they have readers too.
http://www.impinj.com/rfid/rfid-products.aspx
Ti Atmel and others too have RFID products, http://focus.ti.com/docs/prod/folders/print/ri-uhf-00001-01.html
which geography you are in. In Japan We have many local manufacturers.

Yes That is a good idea , you can convert the tag antenna impedance to 50 ohms without chip and connect to a Network analyzer, connect a test antenna to other port and measure coupling. Again there will be some deviation from actual, because of matching , may be we need to use lumped elements to provide tag chip impedance.

Also I have seen in simulation , the tags frequency is affected by proximity of even similar other tags, In simulation I am measuring coupling between two tags(same under development ones) placed close to each other to analyse its performance,

thanks
GV

itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

15 Jun 2008 16:53 Re: RFID tag measurements

Hi GV!

Tell me about the abilty to "program" the RFID tag.
Is it possible?
When fitting the RFID technology into practice how should the designer or/and system engineer should make the most out of the technology?

As an R&D engineer, I need to check this technlogy for an application. Can you recommend me and advise me for some issues I need to be involved in?

Your simulations are very interesting. Keep up with the good work.

Thanks,
IH

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

16 Jun 2008 6:57 Re: RFID tag measurements

Hi,

For feasibility analysis,No need to develop Tag , You can buy (samples will do) readily available Tags (different variety are available) and reader and make real time measurements. Do some theoritical study before buying.

Using RFID for your application also depends on what all other options you have and advantages and disadvantages of all.

Tags are normally of 3 types passive (using back scatter), Semi active (which is capable of receiving input from other sensors) and Active (which has battery inside). So depending on your application range required , on what (metal liquid carton etc) the tag needs to be placed etc etc select one.

Tags can be programmed Using RFID read/write equipments. From PC you can input EPC code into tag, also some other info also like weight colour price etc. can be loaded into Tag.

Regards
GV

itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

16 Jun 2008 12:42 Re: RFID tag measurements

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

16 Jun 2008 13:47 Re: RFID tag measurements

Tell me about the abilty to "program" the RFID tag.
Is it possible?

yes with an RFID read/write device and its software , you can program.

When fitting the RFID technology into practice how should the designer or/and system engineer should make the most out of the technology?

Using RFID for your application also depends on what all other options you have and advantages and disadvantages of all.
depending on your application range required , on what (metal liquid carton etc) the tag needs to be placed etc etc select .

As an R&D engineer, I need to check this technology for an application. Can you recommend me and advise me for some issues I need to be involved in?
[color=darkred]
issues
1. read range , tag spacing , interference, readability near liquids metals, security , cost , application requirements like database user interface ,manupulation of data , alarms required, reusability etc
[/color]
Regards
GV
Regards
GV

boy

Joined: 30 Sep 2002
Posts: 555
Helped: 38

17 Jun 2008 3:58 Re: RFID tag measurements

Please try this paper. The authors of this paper also do RCS measurememt

http://www.edaboard.com/viewtopic.php?p=994423#994423

zirtapoz

Joined: 25 Dec 2007
Posts: 112
Helped: 5
Location: finite space

17 Jun 2008 8:44 Re: RFID tag measurements

itzikhaim wrote:

I.H

Try to use Ansoft designer, and draw the antenna pattern. and put asic(ic) as load whatever impedance it has. And finally use plane wave excitation. U can see the results.. Smile

itzikhaim

Joined: 24 Jul 2006
Posts: 105
Helped: 8

24 Jun 2008 0:50 Re: RFID tag measurements

Hello to all, again!

Can someone tell me what is the protocol of the given RFID tag (label) as shown in attached picture? (e.g. EPCglobal Class 1 Gen 2)

I know that its from Tyco and M/A-Com.
Does the same antenna (tag/label) might be manufactured by other vendor along with their chip?

Last, if I have some tags (as shown), is there a way for me to know what is the type of the class and the protocol this tag uses?

Thanks, in advanced

IH

picture link:
http://www.edaboard.com/viewtopic.php?p=1047622#1047622

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

24 Jun 2008 3:03 RFID tag measurements

go to your link
http://www.edaboard.com/viewtopic.php?p=1047622#1047622

zy032

Joined: 24 Jun 2008
Posts: 8

24 Jun 2008 3:45 Re: RFID tag measurements

hi all
I have the same problem in my study..
i donot know how to measurement the tag antenna's impedance (without the chip)
cause i want to know if my simulation is right.
is anyone know about this or have similar situation?

thanks,
ZY.

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

24 Jun 2008 6:39 Re: RFID tag measurements

Hi
Hope you have gone though Cst_application_note_rfid.pdf given on top of this thread by itzikhaim.

Regards
GV

zirtapoz

Joined: 25 Dec 2007
Posts: 112
Helped: 5
Location: finite space

24 Jun 2008 9:08 Re: RFID tag measurements

zy032 wrote:

As i said before try to download ansoft designer(SW, free) and draw your antenna, put excitaion. and simulate. its easy.

Last edited by zirtapoz on 24 Jun 2008 9:39; edited 1 time in total

zy032

Joined: 24 Jun 2008
Posts: 8

24 Jun 2008 9:23 Re: RFID tag measurements

As i said before try to download ansaoft designer(SW, free) and draw your antenna, put excitaion. and simulate. its easy.[/quote]

but is it just simulation?
i want to measure the antenna after fabrication.. how to do this?.

Added after 7 minutes:

thanks GV.
.. i want to propose a antenna impedance's measure solution.
in UHF band,it is too difficult to get a accurate result.

thanks again.
ZY.

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

24 Jun 2008 9:56 Re: RFID tag measurements

Lets try to understand our requirement.

We have an antenna which is non 50 ohms , say R+J x ohms which needs to be matched to a chip of ipedance R1-Jx ohms. (we need to make R equal to R1, but its difficult in some cases)

Now our measuring system is 50 ohms calibrated, say network analyser.We can match this in 2 ways ,
1. calibrate and make netwok analyser impedance to R ohms , and i think that is not possible
2. so only solution is match the antenna impedance to 50 ohms using known elements (LC matching)and take measurement, back calculate antenna impedance replacing 50 ohms (on a smith chart) with chip impedance.

Also for measuring tag antenna you may require a probe of low pitch , may be a Wafer probe.

Very Happy

I think i am wrong, confused......

Any other method, any comments on this pls.....

regards
GV

zy032

Joined: 24 Jun 2008
Posts: 8

24 Jun 2008 10:13 Re: RFID tag measurements

i have done read the CST rfid example.
in the material, it is said that Simulation of the planar structure with a standard 50 Ωport and then add matching network.
and in the practical application,the IC impedance is R+jx..so,the matching network is not fit here.

Now,my problem is how to measure the antenna impedance without IC,in order to validate my simulation.

regards.
ZY.

zirtapoz

Joined: 25 Dec 2007
Posts: 112
Helped: 5
Location: finite space

24 Jun 2008 12:35 Re: RFID tag measurements

Ok. Lets try for experimental. have you got any vector network analyser? if you have, you get a result applying probe to asic nodes of tag antenna. if you dont have any find a VSWR meter and find VSWR. after that you have to use below equations;

VSWR=1+|Γ| / 1-|Γ| and Γ=Zin-Z0 /Zin+Z0

Z0.. characteristic impedance of feed line (actually 50)
Γ... measure of reflected signal at feed point.

Zin ll be your result.

refer link for:

http://autoidlabs.eleceng.adelaide.edu.au/tutorial/Antmatch.doc

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

24 Jun 2008 14:31 RFID tag measurements

Thanks zirtapoz. the Doc is useful.

zy032

Joined: 24 Jun 2008
Posts: 8

25 Jun 2008 5:13 Re: RFID tag measurements

hi zirtapoz
.i cant open the site.. my net is restricted i guess ....
would you pleased post it as postscript here.

however,i am still comfused about the RFID antenna impedance measurement.
as: 1.how to get VSWR?in UHF band,the common probe isnot accurate anymore.
2.the antenna is printed on PET,i think normal way for measurement isn't suitable here.

..more and more comfused... some comments plz..

thanks.

ZY.

GVVIN

Joined: 11 Apr 2008
Posts: 88
Helped: 14

25 Jun 2008 6:41 Re: RFID tag measurements

yaa for measuring antenna in PET I think you need Wafer probe or similar stuff, you cant solder cable and all to silver ink.

attached is the doc, just some basic, still the real problem exist.... Very Happy

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zirtapoz

Joined: 25 Dec 2007
Posts: 112
Helped: 5
Location: finite space

25 Jun 2008 8:57 Re: RFID tag measurements

Yes problem is still alive. Because of determining experimantal VSWR or impedance etc problem; i said use a simulation tool and trust it. that is better.(Do you think that tag manufacturer is determining their measurement one by one??)
in real life they are using some printed antenna over some thicker subrates than pet. Simulating it. measuring it. and after succesfull results they are changing subrate and simulating finally. There may be some other ways to measure VSWR too.(such as building your own VSWR meter) But hard to implement.(For instance: you may connect 50 ohm circuit to the asic pads on antenna(use surface mount equipment on tag side with suitable welding). and after that you send signal from a specific distance. And measure. repeat operation with any antenna having known measurement. And compare the results!! Very hard way.. i ll still simulate... Smile

zy032

Joined: 24 Jun 2008
Posts: 8

25 Jun 2008 10:00 Re: RFID tag measurements

hi zirtapoz
as what you said,in real it is impossible to measure the antenna one by one..
but now my problem is a lab work.
I need a way to prove my simulation is right or not... i mean.. i dont know if the simulation is accurate without the comparation between measured result and simulated...
do you mean measure the FR4 antenna instead of PET one to testify the simulation work?

thanks..
ZY.

zirtapoz

Joined: 25 Dec 2007
Posts: 112
Helped: 5
Location: finite space

25 Jun 2008 14:12 Re: RFID tag measurements

yes. maybe. or other type of subrates. All ll work, or if i m not right ;Maxell had to be fabulist... Smile

fox244

Joined: 21 Jul 2008
Posts: 1

21 Jul 2008 18:57 Re: RFID tag measurements

hi guys
i have this problem too i make an rfid passive tag in uhf band
my antenna is a replied dipole and i don't make an measurement of impedance caus eil dipole an my merasure is wrong
have u any idfeas pls
regards

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