[SOLVED] UHF RFID antenna Impedance Measurement without anechoic chamber

[Techi]

Dear All,

I want to measure the impedance of UHF RFID tag antenna and my problem is that I have no access to Anechoic chamber. Please suggest me some solution to measure the impedance without Anechoic chamber with better accuracy.

Thanks

 

[tony_lth]

Just test it in outdoor and use VNA test S11, then get Zin.

There are several similiar threads in this forum, you can search it,

 

[MobiNaz]

Check in free space. Can I ask, what type of RFID is it? Application?

 

[Techi]

It is 866-960 MHz rfid antenna. The main problem is how I can bring all the testing instruments in free space while they are in lab. Is there any possibility to arrange some stuff like (RFabsrorber) urethane-based foam. what u say?

 

[vfone]

https://www.edaboard.com/threads/43779/

 

[Techi]

hi I just want to measure the input impedance for conjugately matching with rfid ic. ithink this needs nead field chamber. please guide

 

[streamlet]

It is 866-960 MHz rfid antenna. The main problem is how I can bring all the testing instruments in free space while they are in lab. Is there any possibility to arrange some stuff like (RFabsrorber) urethane-based foam. what u say?

RF absorber may help. Generally speaking, it is OK to test the input impedance of tag antennas in lab condition. Just make sure nothing shows up in the near field of tags, esp. metals, water, high-permittivity dielectrics. You should pay attention to calibrate the influences of cables.

 

[Techi]

Thanks! you really got the exact point. I can go with option of RF absorber. the size of the antenna is 12cm by 3cm. so what do u suggest about the Rf absorber dimensions. Pls do let me know if you have some link from where i can buy the RF absorber.

 

[FvM]

My general expectation is, that the impedance error introduced by the connection cable will be a multiple of effects from some enviromental reflections. That's at least what I found with impedance measurements of UHF antennas.

 

[Techi]

Hi FvM, Thanks! I will do the testing in the lab and its not shielded and there are other instruments in there which I will turn off and like Streamlet suggested I will use RF absorber around the antenna so that the measurements should not effect much from environment. Pls do u have any clues of buying Rf absorber for 860Mhz-960Mhz.

 

[FvM]

I didn't use absorbers up to now. My basic sugeestion is to move the antenna e.g. tilt it, or potential near by reflectors and observe the S11 sweep display on the VNA. If it doesn't change considerably, you can expect the enviromental influence to be low. Or place artificial reflectors or partial absorbers (your hand) near to the antenna to get a feeling about the expectable influence.

 

[Techi]

Hi, I am able to get standard absorber AEPXX from **broken link removed** . Can you please tell me which one I should get and how much is needed. Sorry I am asking quite much help. Thanks

 

[vfone]

The last desktop enclosure that I made while ago for similar purpose, has the following external dimensions" L=1.5m, W=1m, H=1m, and a big access window at the front.
I made two models, one using small pyramidal absorbers (12"), and one using laminate absorbers (flat). Pyramidal type would be better in terms of reflections and test repeatability, but you get less space inside of the box. If the test frequencies are greater than 1.5GHz would be fine less space.

 

[Techi]

In my case I need to test it on 860Mhz-960Mhz so I think ur mentioned dimensions sounds perfect. Can I use the wooden box of the dimensions mentioned by u and fix the rf absorbers in it? or what u suggest. Thanks a lot for ur guidance

 

[vfone]

Yes, wooden box is ok, I used the same. The dimensions are not critical, you can follow the dimensions of a lab desk.

 

[Techi]

Thanks! I am in process of making the wooden box so should I leave one side of 1m width completely open or I should place a door on this side with a big hole to pass the cables?

 

[vfone]

Myself I let only a 0.5m wide window at the front, but probably 1m would be fine.
All the cables MUST be routed under the absorber material.

 

[Techi]

Thanks for the help. What type of adhesive I should use to fix the foam with wooden walls. Or I can use any avaialble adhesive that can fix the foam?

 

[vfone]

Any type, because is on the back of the foam. I remember the foam manufacturer recommends some adhesives.