# How to create a 13.56MHz PCB antenna in Eagle?

How can I create a 13.56MHz PCB antenna in eagle since I can't find any suitable antenna library in Eagle, even failed to download 13.56MHz antenna .lbr in the internet. Kindly help

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c / 13.56MHz / 4 ~= 5.53m –  Ignacio Vazquez-Abrams Apr 4 '14 at 5:31

SparkFun have this RFID Evaluation Shield that works on 13.56MHz. They provide the Eagle files which contain the antenna portion. You could either use this for ideas or take the antenna portion from the .brd file.

Copying this sort of antenna is not a simple case of copy and paste. If you look at the schematic you will see this section with C2-C7:

This relates to the following portion of the board:

These capacitors and two resistors (used as jumpers) tune the PCB antenna to work well on the chosen frequency. If you choose to copy the antenna then make sure it's as close to the original as possible. This means trace width, spacing, the feed line from your driver etc, even the PCB manufacturing process might make a difference. If you keep it virtually identical to the original then you might get away with the capacitor values used by Sparkfun.

You might like to check their licensing model if your application is commercial.

Images in this post from Sparkfun, licensed CC BY-NC-SA 3.0.

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You are not thinking about this correctly. The antenna itself is not 13.56MHz - it's just an inductor made from copper on the circuit board that requires tuning with a capacitor. When tuned with exactly the right capacitor, the inductance of the copper track/loop and the capacitance of the capacitor form a tuned circuit corresponding to the following formula: -

$F_C = \dfrac{1}{2\pi\sqrt{LC}}$

Given the above formula there are a wide set of possibilities to choose from so, roughly copy what @David is saying and then fiddle with the tuning capacitors to get peak tuning and optimum Q (quality factor for the tuning). Read the data sheet on the device you are interfacing it to because that will give you the info you need to get this right.

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I have designed a NFC antenna before (assuming you are using NFC due to this particular frequency :P).

I experimented with a ST NFC antenna, ANT1-M24LR16E.

On its webpage is also a tool for antenna calculations and it's application note.

Note that antenna design is quite tricky and your first antenna might not work. Although using this tool, my first antenna design did work right away. You can include a footprint of a capacitor parallel on your antenna so it can be fine tuned later.

Hope this helps.

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