13.56meg RFID tag antenna (urgent)

Hi !
I need urgent help with this, may be a similar example or general guidelines for me to follow
I am making a very simple RFID tag on PCB for which i need to design a microstrip antenna
The requirements are:
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tag antenna
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Freq=13.56meg
BW=10K
Current capability=1m
Signal voltage>=1v
Area: whatever it takes for it to work well
Load model
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R=24.1429k
C=1.24957n
Reader
------
Tx power=4w
distance between reader and tag>=1m
Available software:
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Orcad Pspice capture
microwave studio
I hope i am not missing something, if so please ask me
Thanks Guys

This might help concerning Simulations of your loop
Simulating Q of circular planar coil(you can search this topic in our forum)
Theres also a"good" AN from microchip, but do note that it does not model the AC loss correctly.
Hope this helps!

ok, first of all thanks darkcrusher, i appreciate your help
I will try to extract what is useful from at its time
But now i have a question, as i said before the circuit capacitance is approximately 1.25n and for the antenna to resonate at 13.56meg the inductance value would be less than 1uH ! is this realistic ? all examples i have seen so far, the inductance is approximately 5uH may be a little lower or higher, this is because the input capacitance is usually hundreds of p's, so my question is: can the antenna inductance be less than 1u and still can gather enough energy to supply a 2v peak to peak signal at its terminal considering that distance must be no less than 1m and the area is not a critical issue ? if yes then i will proceed but if not then what am is supposed to do ? is there a way to reduce the input capacitance without modifying the circuit ?
Again guys please any help would be appreciated

Some parameters of your specification don't sound well considered. E.g. an "antenna" bandwidth of 10K would imply an excatly tuned resonant circuit, which would be neither reasonable nor feasible at all. All practical 13.56 tag antennas are multi turn coils, you can refer to manufacturer literature and also reference antennas in RFID standards. I guess, "microstrip" is just a vague term for a printed antenna?

Yes, you are right FVM, may i modify the statement to be as following:
the attenuation at frequencies within +-10K from 13.56meg should not exceed 3db, i guess the Q should be within 10 and 15
May i ask what else does not seem well considered ?
Also, i have already some papers from which i am trying to learn, but this is a whole new thing to me and unfortunately it's urgent, it must be done before the end of the next week, that's why i am asking for help
Any way, thanks, i appreciate your help
By the way, the inductance being less than 1uH (see my previous post) does it seem realistic to you ?

Hi,
Theres also a sonnet application note on the design of RFID coils
A few hundred nanohenries seems reasonable
Good luck

I downloaded sonnet example but i couldn't run it cuz it has more layers than permitted with the program demo available for free download
What can i do ?

An RFID coil is basically a pure magnetostatic problem, because the dimensions are very small compared to wavelength. The only RF related phenomenon to be considered is the skin effect. Also the transmission between reader and tag can be treated as a magnetostatic problem, as long as you don't need to calculate the generated far field. But even emc rules for RFID are only referring to magnetic field.
You can use a full featured EM solver for RFID coil analysis, but a basic magnetostatic tool like FastHenry from fastfieldsolvers.com can do as well. I have used it for analysis of various ISO 14443 (proximity RFID) problems, and the results are in accordance with measurements.
But you can also refer to manufacturer application notes for ISO 15693 and 18000-3 RFID systems, e.g. from Texas Instruments. TI has an "Antenna Cookbook" dedicated to the design of large reader coils, and tag coils should be discussed with the respective chips. But I'm not working on vincinity RFID, personally.

Thanks FvM
and Sorry for being late, i have been a little busy doing another project
Anyway, i started to make a good idea about the flow from whatever i have read, today i will start investigating some tools and choose one, but until then i hope if someone can tell me what to do with this: my teacher asked me to look also for an already made antenna and buy it, just in case mine did not work, i found this digikey site where there were some antennas for the purpose i was looking for, however i want to make sure is this suitable ? for example, i attached the one which got my interest, does it work only with some specific tags ? or could it work with mine ?
ID ISC.ANT800_600_DA_E.pdf

Confusingly, you have been asking for a tag antenna up to now. For reader antennas, the said TI antenna cookbook has several interesting design suggestions, as already mentioned.

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