PCB antenna design problem: too short range?

[angel]

Dear Nordic,

Some time ago we started a project in which we decided to use ANT protocol to communicate wirelessly. However, now that we are going to production in a very very short time, we have spotted a very critical problem in the range of the communication.

Here is the design of the antennas, in emitter and receiver pcb designs:

And here is the schematic for both of them:

The total length of the antenna is 28.13 mm and the width 0.35 mm.

The main problem is that we only have like 1 to 1.5 meters of acceptable range. If I use the nordic DK as TX end, the range is significantly bigger, like 4 to 5 meters. This would be enough for our application.

Also, it is important to state again that the PCBs are already in production, so a solution requiring minimum changes in hardware would be better.

We have already tried different frequency numbers by SW (from 2400 MHz to 2524 MHz), but that only helped a bit (2433 MHz) seems to work a bit better.

Also changed the RADIO_TX_POWER to +4dBm but didn't really do anything.

Anyone has any idea how we could improve the range of our antenna? Again, I know that the same software using the DKs has a really good performance.

Thank you very much for your help.

[Dave_couling]

You need to add a Pi network after the Balun so you can tune the antenna. Did you use an impedance calculator to determine your trace width? Is this from a reference design? I hope you're design has a ground pour that was omitted from your photos. Reference ground size and consistency is crucial to good transmit efficiency.

[MANGO]

Hi, Angel. I think there is a minor issue with the ANT1 (31) and ANT2 (32) pin.

it is important to state again that the PCBs are already in production, so a solution requiring minimum changes in hardware would be better.

Hmm, I hope for your understanding that my answer won't be a big help.

While waiting for a better solution / answer provided by the Nordic's dev-team, take a look at my answer, please.

This issue was detected from the Nordic's distributor when I was creating a custom PCB that uses nRF52832.

Take a look of the PCB traces of pin 31 and 32, please.

ref. Nordic devzone - PCB Antenna. Tuning not necesary

ref. Nordic Blog - General PCB design guidelines for nRF51

Both traces are symmetric; they are stretched with the same length and bent at the same y position.

As a result, the balun's center is aligned to the center of pin 31 and 32.

Also, as you see the blog's picture, there are plenty of ground vias at the nRF51 MCU footprint.

Whereas,

your trace is not symmetric. The trace of pin 31; it is bent "earlier".

So the balun's center is not aligned.

Also, I can't tell whether your PCB has sufficient ground vias at the nRF51 MCU footprint.

This type of issue has an effect on matching network.

Like "Dave" 's comment, have you used an impedance calculator?

Also, how is the ground pour configured below the matching network?

-Best Regards

[angel]

Hello Dave, thanks for your answer! We didn't use a Pi network because we thought that it was not necessary when we use the matching balun that we are using.

Also, we didn't use any impedance calculator, we just copied the design of the antenna from the development kit files (dongle nRF51), and tried to maintain our design as close as possible to that reference design.

About the grounding, just below the antenna we have a big ground plane, connected through vias to the lanes that you see in the picture above. Do you think this is sufficient as ground pour?

Thanks again Dave!

[angel]

Hi MANGO,

First of all, every answer is of very good help, thank you very much for your reply!

I see that you in the thread that you link, in the end, the decision of removing the Pi network is taken. We also have no laboratory equipment available to do these tuning measurements, so I assume that for us is also useless to put a pi network there.

As I wrote as a reply to my previous question, there is a ground plane right below the antennas, that is connected through these lanes that you see next to the antenna. Do you think that it is enough grounding?

About the centering of the Balun, do you think it will affect a lot if we align it? I mean, can it affect significantly to the range of the antenna?

Thanks again for your reply!

• Best

[Jørn]

Hello Angel. Just to be clear, you say there is a groundplane underneath the antenna. Does the groundplane actually cover the area directly underneath the antenna itself? In other words, have you maintained a keep-out region on all layers underneath the antenna?