How to use a Murata u.FL MM8130 connector to adjust the impedance matching network between the nRF52 SoC and the ceramic antenna

[gcb]

Hi,

I'm using an nRF52840 DK to develop my prototype. Now I'm moving into the PCB design phase and I'm using a BLE ceramic antenna. I'll add a pi network footprint to tune the antenna to the nRF52840 RF signal.

Something I noticed on the nRF52840 DK is the Murata u.FL MM8130 connector between the SoC and the ble antenna. Based on the connector datasheet, when an SMA connector is plugged in, the Murata connector will open the internal switch and therefore isolate the pi network and antenna from the SoC, allowing us to perform some RF measurements directly to the SoC.

if I rotate the u.FL connector 180º, and plug a connector into it, I will isolate the nRF52840 SoC from the antenna and my measuring device will only be connected to the pi network and the antenna, am I right? In this situation, if I connect a VNA to it, I can see if the pi network is matching a 50-ohm impedance, and if not, tune the pi network to achieve a 50-ohm impedance. Am I missing something here?

Best regards

gcb

[mathiaso]

Hi, gcb.

Your thoughts are right. Just make sure that your radio isn't transmitting when you're measuring the antenna, as some power transfer might happen even if the internal connection is open, due to radiation. Also make sure to include your prototype's enclosure when tuning the antenna, as this is likely to impact how it resonates.

If you do not want to tune your radio and antenna yourself, beware that we offer a free-of-charge tuning service to our customers.

Best regards,
Mathias

[gcb]

Hi

mathiaso said:

Just make sure that your radio isn't transmitting when you're measuring the antenna, as some power transfer might happen even if the internal connection is open, due to radiation.

Yes, to tune the antenna using a VNA I will make sure the PCB is turned off.

mathiaso said:

Also make sure to include your prototype's enclosure when tuning the antenna, as this is likely to impact how it resonates.

What do you mean by prototype enclosure? Like a metal shield around the nRF52 SoC and all the necessary passive components like capacitors, crystal, etc.?

mathiaso said:

beware that we offer a free-of-charge tuning service to our customers.

I did not know that. Thanks for mentioning this. Great to know.

[mathiaso]

gcb said:

What do you mean by prototype enclosure? Like a metal shield around the nRF52 SoC and all the necessary passive components like capacitors, crystal, etc.?

I'm just thinking of the casing of your design, to make sure everything is similar when tuning as when the design will be used for its purpose.

gcb said:

I did not know that. Thanks for mentioning this. Great to know.

You're welcome! :)