NFC antenna design

[EthanMathew25]

Hi, 
I have been trying to design a NFC antenna for the past few weeks and I have been very unsuccessful with it so-far. I am using NXP's NTAG IC ( NT3H21111). I have read the application note that comes along with it and I have also gone through the other manuals and resources available with respect to antenna design for the particular IC. 
I made use of the tool provided by NXP to design the antenna. I made the design in Ansys AEDT 2023 R2 ( Student ) and I have simulated it but I am not getting a proper |S11| curve. I've tried different combinations of dimensions but still I am not able to get a proper result. I don't know where I am going wrong, any help with regards to this matter would be great. Thank you.

[Tomas_Parizek]

Hello EthanMathew25, 

See an example below: 

I typically use a classic via between the top and bottom layers. The feeding is done with the help of the "Discrete port". I guess there is something similar in HFSS. 

Tomas_Parizek_0-1704700506066.png

Regarding the port, I use only one port in "differential" configuration. This is more convenient for NFC. 

The same should be possible in HFSS as well. 

Tomas_Parizek_1-1704700925612.png

BR

Tomas 

[EthanMathew25]

Hi Tomas,

Would you be able to share the project files for CST Studio mentioned earlier? I tried using Ansys HFSS, but I haven't achieved any results. I'm just getting started with CST Studio (student version), and I attempted the same structure. However, since I'm new, I'm still navigating the learning curve. If you could share the file, it would be greatly appreciated.

Thank you.

[EthanMathew25]

@Tomas_Parizek 

[Tomas_Parizek]

Hello EthanMathew25, 

Here you go. 

BR

Tomas 

[EthanMathew25]

Thank you!

[EthanMathew25]

Thank you Tomas, I'll try these and get back to you. I have also made some changes to design, have been able to get my S11 to 11GHz.
I'll try and get back to you.

[Tomas_Parizek · Accepted solution]

Hello EthanMathew25, 

Thanks for your question!  

I typically use CST Microwave but the principle is more or less the same as in HFSS.

Once you have drawn your antenna :

E.g. 

Tomas_Parizek_0-1702984461797.png

You need to check the basic antenna parameters as Inductance and Resistance: 

Tomas_Parizek_1-1702984586709.png

You can see that the Antenna inductance is L= 354nH and resistance R=0.51R at 13.56 MHz. 

Then I recommend switching to the "schematic" view (in HFSS should be the same option) and connecting the antenna with the equivalent RF model of the NTAG I2C (10K parallel with 50pF). 

See below: 

Tomas_Parizek_2-1702984991066.png

I would also highly recommend switching to the "smith-chart" view. Then you can see the NTAG I2C + an antenna impedance: 

Tomas_Parizek_3-1702985235257.png

To have a proper impedance tuning, you need to add a tuning parallel capacitor as shown below. 

Tomas_Parizek_4-1702985352042.png

The target is to have the 13.56 MHz  "resonance point" on the real axis an shown below: 

Tomas_Parizek_5-1702985416422.png

Then, you can also visualize the magnitude of S11:

Tomas_Parizek_6-1702985503917.png

But as mentioned above. For NFC, I would fully recommend using the Smith chart

BR

Tomas 

[EthanMathew25]

Hello @Tomas_Parizek , thank you for your response. Could you provide additional details about your design? In my design, the resistance is quite low from ReZ(1,1)

Where did you implement the excitation in your design? How did you establish the connection between the inside and outside? Did you use vias, connecting them from the bottom, or did you employ a bondwire-like structure? and also is your antenna a two port device ?  do we have to excite two ports ?

thanks.