How to find inductance of RFID multiturn Loop antenna

[sr_raval]

Dear All,

I have designed one RFID PCB loop antenna,how can i calculate the inductance of the antenna?i dont have LCR meter or any other measuring instruments,if i will get the inductance from that i can able to calculate total parallel capacitance,now how can i distribute this capacitance in to series and parallel capacitance,as per my circuit i have to solder series and parallel capacitance both,if you want any documents from my side i will give you....

Please help me.....

 

[FvM]

You'll find rules of thumb in RF handbooks and amateur radio literature. For complex geometries, e.g. PCB coils, I prefer a measurement or a numerical simulation. FastHenry from https://www.fastfieldsolvers.com is a good free tool.

You'll need a method to fine-tune the circuit after making it, so an oscilloscope and either a signal generator or the reader IC of the final design would be needed. It can be used also to measure the actual inductance by connecting a known capacitor. You don't need a LCR meter.

 

[sr_raval]

thank you for your valuable reply,what i want to know i will explain you by example.
say for example if i have total parallel capacitance 200pf,how can i distribute this value in to series and parallel capacitance,means what would be the series and parallel capacitor value?i am unable to download tool from the site you suggested.

 

[FvM]

I checked, that the site is working. Here's the direct tool's link:

But the tool is for inductance calculation only, not for design of resonant circuits or filters. I guess, you intend a matching circuit like the below Philips/NXP application? Viewn from the coil, the parallel and series capacitors are simply added. Generally, the series capacitor is smaller by a factor of e.g. 10 to provide the impedance transformation, so the parallel capacitor mainly determines the resonance frequency.

 

[sr_raval]

I have this document but my confusion is as under
1) first find out the exact inductance and series resistance of the antenna,i don't have any measuring instrument
2)according to inductance i have to find the value of C1a,C1b,C2a and C2b

 

[FvM]

1) I suggested FastHenry, any of those high end EM simulators could also do, of course. As I previously mentioned,
I can hardly imagine to put the circuit in operation without measuring instruments. The usual RFID reader circuits are
high Q and most likely need fine tuning.

2) It's a RLC network, standard network theory applies. If you aren't motivated
to figure out the exact expressions, use an electronic circuit simulator to evaluate
the circuit behaviour.

 

[sr_raval]

which simulation tool you prefer?