# Calculate inductance and capacitance of a double layer antenna (RFID)

I want to design an antenna that will work with RFID NFC chip NHS3152.

The NHS3152 IC specs are:

IC capacitance at precise measurement conditions

For this particular IC, there is a demoboard.

Since I have the schematic (Gerber: download_link It can be opened with This online tool ) files of the antenna I want to:

• Calculate the L and C of the demoboard antenna
• Design my own antenna (which if it has similar specs should work)

From the schematic however, you can see that the antenna is double:

• BOTTOM antenna loop on the bottom layer (here in red)
• TOP antenna loop on the top layer (here in blue)

The TOP and BOTTOM antenna loops are separated by the PCB, however they are connected to the same pads.

• How do I calculate the L and C?
• Is there an easier way to find an antenna that will work with the NHS3152 chip? (For example: all antennas from a certain standard or something.)

EDIT in response to @Andy aka comment:

Here is the ZIP of the gerber file in question: https://github.com/Pr-ROXFET/Stack_docs/blob/main/NHS3152%20Demo%20PCB.zip?raw=true, that can be opened this this online gerber viewer This Gerber design antenna must work for sure, as it is the design of NHS3152Demoboard, a product of NXP that I am currently using (and is working)

EDIT: instruction to open Gerber file :

EDIT: Screenshot Bottom and top:

• That mag-loop doesn't look to me like it would work given the connections (red and blue) shown. Jul 16, 2021 at 11:11
• @Andy aka I have edited the question with a downloadable Gerber file link: the antenna design must work, as it is of a DEMO board of NXP, which i am currently using
– Leo
Jul 19, 2021 at 7:05
• That gerber file doesn't properly open using on-line gerber tools. Jul 19, 2021 at 7:15
• try this one: gerber.ucamco.com/timeout.html it works for me!
– Leo
Jul 19, 2021 at 7:16
• I strongly suggest that you do what you have instructed me to do and notice the obvious differences between what you have posted and what you have just offered as gerber files. Jul 19, 2021 at 7:20

## 1 Answer

The layers with teh antenna are .BOT and .SST

SST stands for "silk screen top" and it is not a copper layer. These are the copper layers: -

This is the SST layer: -

And IT ISN'T COPPER.

• Thanks, so the SST layer ins't copper traces, this makes a lot of sense (very new to PCB design here as you can tell) , thank you.
– Leo
Jul 19, 2021 at 7:49
• is there a reason why the SST layer doesn't trace precisely the antenna, but rather does that crossover? convention or just designer's discretion?
– Leo
Jul 19, 2021 at 7:57
• The SST layer is a visible information layer and may or may not bear some or little resemblance to reality @leoelectrics Jul 19, 2021 at 8:09