NRF52832 Layout review and antenna design

[Hani_Montana]

Hello everyone,

I created my first own layout design and the antenna. Before I order the PCB I hope you guys can review it one time. I tried to get the most informations from the forum, but I was not able to answer all of my questions. The PCB has a size of 12mm x 43mm and has only 2 layers, therefore I was not able to take over the reference layout. I tried to take over as much as possible from the reference layout of the NRF52832. I used the tool EasyEDA for designing the schematic and layout.

I never designed a antenna before and I tried to copy the design from the NRF52840 dongle. Which range can I expect from this antenna? I read alot regarding the 50Ohm Impedance, but i didnt completely get from where to where is the 50 Ohm. I know there is a matching circuit C3 and L1 the µC see a Impedance of 50 Ohm. Where I need to design the next 50Ohm from L1 to R9 or from L1 to end of the antenna?

Can you please give me a feedback if the device and antenna will work? And if not please give me a feedback what I could improve. If you need any additional information I will deliver them as fast as possible.

The Top Layer:

The Bottom Layer:

Schematic:

[Bendik Heiskel]

Hi,

1. There must be continuous ground form under the center pad and under the entire RF path, from the ANT pin to the antenna feed point. This means that the traces running under the RF path must be moved.

2. The center needs a good ground connection, we recommend a 4x4 via grid connecting it to the bottom layer ground.

3. This type of antenna should have a complete Pi network for antenna matching. The antenna impedance is dependent on the size of the ground plane and the enclosure for the PCB, using a Pi network gives more options during antenna tuning.

 

Best regards,

Bendik

[Hani_Montana]

Hi Bendik,

I updated your 3 points can you please recheck? I added 4x4 vias at the center pad. I moved the traces under the antenna path and floated it with ground. You saied "complete pi network" for antenna matching. I added now an additional capacitor.

How can I calculate or check the 50 Ohm impedance and from where to where I have to consider the 50 Ohm? Is the antenna size good and which range can I expect with this antenna? Is the PI antenna the correct antenna for my PCB or is it better to use a meander antenna?

I expect a range of minimum 10 meter.

Best regards

Hani

[Bendik Heiskel]

Hi Hani,

This looks better, but there should be some more vias connecting the top and bottom layer grounds close to the RF path and antenna.

Hani_Montana said:

How can I calculate or check the 50 Ohm impedance and from where to where I have to consider the 50 Ohm?

You can calculate the transmission line impedance by for example using AppCAD or other calculators for a grounded coplanar waveguide. Remember to select the correct substrate, which for regular PCBs are FR4. There must be an impedance of 50 Ohm between the radio and antenna matching networks, so in this case the trace between L1 and C22.

Hani_Montana said:

Is the antenna size good and which range can I expect with this antenna? Is the PI antenna the correct antenna for my PCB or is it better to use a meander antenna?

Using this meander antenna should work, but it is important that the antenna impedance is tuned to 50 Ohm, this must be done using a VNA to measure the impedance and change the values for C22, R9 and C23. The range of the antenna is dependent on many external factors so I can really estimating the range in meters. But with a properly tuned antenna you should be able to get more than 10 meter range.

 

Best regards,

Bendik

[Hani_Montana]

Hi Bendik,

thank you really much for your support! You helped me alot. I added some additional vias and calcualted now the Impedance. From my point of view it looks fine.

I think I can place the order now .

Best regards

Hani

[Bendik Heiskel]

Hi Hani,

This transmission line impedance should be fine.

If you would like us to tune the radio and antenna matching networks you can open a private case and one of our hardware engineers will give you the required information. Keep in mind that we need at least two fully working samples of the boards for the tuning.

 

Best regards,

Bendik

[Hani_Montana]

Thank you very mich! Once the hardware is working and I am at the Pointe to tune the antenna I will statt a privat ticket.