TRF7960 antenna size

Hi Jerome,

This antenna should be ok as long as you are driving the TRF7960 with 5V in full power mode.  I have used a 300mm x 300mm antenna from Feig Electronic with the TRF7960 succesfully.  This is about the largest size you can go without an amplifier though.  You can find the read range of the TRF7960EVM with the 300x300 antenna attached.  This document also shows read range with the same antenna and some higher power readers. 

The other thing to consider is the tag size.  For very small tags, the magnetic field needs to be more concentrated.  Very small tags generally do not work well with larger antenna sizes unless you are putting out more power.  What size tag will you be using?

Best Regards,

Eddie LaCost

Hello Eddie,

Thank you for your answer !

I am using 36mm round tag (ISO15693). What was the design of your antenna ? How many coils did you do ? Is the read range achievable with a PCB antenna ?

Thank you for your help.

Jerome,

This antenna was manufactured by Feig.  See the link below.  I believe the Feig antenna uses a single turn aluminum tube. 

http://www.feig.de/index.php?option=com_content&task=view&id=493&Itemid=128

It should not be too much trouble reaching 5cm range with a PCB antenna this size and 36mm tag size.   You should aim for about 1uH for your coil inductance.  Use the attached software to calculate number of turns.  I think 1 turn with 0.5mm trace width would work well.   This should put you around 958nH.  You could also prototype this with 22AWG copper wire.  The TRF7960TB Users Guide has some good information regarding the antenna tuning procedure.  Let me know if you have questions about this. 

TRF7960TB Users Guide: http://www.ti.com/litv/pdf/slou297

The last thing to consider is the Q of the tag.  I am only aware of the 36mm tag that comes from Avery Dennison.  Is this what you are using?  We also have a 32mm circular tag intended for CD/DVD that may work well.  If you are interested, let me know and I can send some samples.

Best Regards,

Eddie LaCost

Thank you very much for all this information.

Do you know the software used in the TRF7960TB User Guide for the Smith Chart simulation ? I use RFSim99 but I cannot enter ZL = 0.8 + j80 (for instance).

My actual PCB antenna is about 450nH (0.1 + j38).

The tags I use are the CD type from TI i think (maybe ri-i17-114a-01), 5 or 10mm in asphalt or concrete, and the antenna will be about 30mm above the floor. Do you think it is possible to read the tag without amplifier ?

Thank you again.

Jerome

Jerome,

The Smith Chart software can be found at Professor Fritz Dellsperger's website.  It is quite useful.

http://www.fritz.dellsperger.net/

I think you should be able to hit this range requirement.  Is the tag going to be read when the concrete is wet?  You may actually do better with our 22mm encapsulated tag.  This tag is smaller in diameter, but uses a copper wire antenna which has a higher Q, so range is quite good.  This encapsulated tag also works very well in liquids.  You can find links to the 256 bit and 2k bit versions below.

256 bit: http://focus.ti.com/docs/prod/folders/print/rf-hdt-dvbe.html

2k bit: http://focus.ti.com/docs/prod/folders/print/rf-hdt-dvbb.html

In future versions of this antenna, you may want to make your antenna trace skinnier to increase the inductance to closer to 1uH. 

Best Regards,

Eddie LaCost

Hello,

Thank you very much for your help. I now have antennas with very good read range (around 10cm I think).

Do all the 13.56MHz antennas must be close to 1uH ? Why ?

Thank you.

 

 

 

Jerome,

Glad to hear that.  Good work!

~1uH is not a hard requirement, but rather a best practice.  When your inductance is around 1uH, this allows for commonly available capacitor values to be used for tuning.  You will also see in figure 11 of the TRF7960TB reference guide that at a given Q, the parallel and series caps will be equal.  For this antenna with inductance of 0.95uH, this occurs with a Q of just less than 7.

Please let me know if you have other questions. 

Best Regards,

Eddie LaCost 

Hello,

I try to use the Small Loop Inductance Calculation tool, but it does not let enter Trace Size of 0.4mm...

I hope TI could correct this bug, or maybe someone knows a better tool ?

Thank you.

 

No answer in 3 weeks ? Thank you...

I can see on the Evaluation module of the TRF7960 that the wire ground is inside the antenna. Is it very important to keep it inside the antenna ?

Thank you.

Jerome,

I apologize for not replying earlier. 

We do have another inductance calculator that allows for trace width smaller than 0.4mm.  This is attached.  You will need to go to file->trace size to enable this.

If I am understanding your question correctly, you are asking if the ground connection can be on a board seperated from the antenna board.  This is not a problem.  If I did not understand your question correctly, please explain.  Thanks!

Best Regards,

Eddie LaCost 

Thank you for your answer.

As I thought I did not manage to explain myself clearly. I'm trying again.

When drawing a PCB antenna, there is one wire that ends inside the antenna, and the other ends ouside the antenna (see the 2 arrows in the picture).

So my question is : which one should be connected to GND and the other is the signal ? Is it important ?

Thank you.

Jerome

 

 

 

Thanks for the clarification. 

It really doesn't matter which end is connected to ground as long as the opposite end is connected to the series tuning components.  The loop is creating an inductor so there is no polarity.

Best Regards,

Eddie LaCost

Thank you.

I tried the software Small Antenna Design, but it does not work : I can open it and change the values, but when I clic on "Calculate" there is a pop-up "Error '13' Type incompatible".

Jerome,

I am not sure what the problem might be with that software on your machine. 

I just looked at the originally sent small loop inductance calculator and it seems to allow 0.4mm trace width and smaller without error.  Did you receive an error when trying this trace size?

Best Regards,

Eddie LaCost 

Sorry if this is a bit off-topic.

I'm a student and I am working on the design of a 'long range' RFID reader (0.5m) as my degree project, I was studying the power amplifier design for TRF7960 that TI provides, but it says very little about the antenna for this amplifier.

I was also reading the following:

http://www.ti.com/rfid/docs/manuals/appNotes/HFAntennaDesignNotes.pdf

In that application note a program “ADU.EXE” is mentioned for calculating the inductance of the antenna, where can I get that program? 

Is the program provided by Eddie LaCost suitable to calculate the inductance for this tube antennas? 

Any help would be appreciated, thanks in advance

hi ,

could you tell me which antenna are you using ?

actually I am using the NFC wire loop antenna, and tag is ISO15693 , which is only detect 5cm I want , it detect 10cm .


could you tell me how can I interface these Antenna to TRF7960A ?