Antenna selection guidance for nRF52840 DK

[Venu Madhav Murapaka]

Hello Nordic Community,

We are currently using the nRF52840 DK for BLE testing and controlled BLE interference generation in a lab environment, primarily in the 2.4 GHz band.

We would like guidance on antenna selection for this use case. Specifically, we would like to understand the following:

1. What are the key things to keep in mind when selecting an external antenna for the nRF52840 DK (e.g., gain, impedance, radiation pattern)?

2. Since BLE operates in the 2.4 GHz ISM band, is it acceptable to use standard 2.4 GHz Wi-Fi antennas with the nRF52840 DK for BLE testing and interference scenarios?

3. Is there a recommended antenna gain range (for example, 2–3 dBi vs higher-gain antennas) to ensure realistic and repeatable BLE behavior?

4. Are there any known caveats when using higher-gain or directional antennas with the nRF52840 for radio_test or continuous TX use cases?

Our goal is to keep the setup representative of real-world BLE devices, while still being suitable for controlled interference and stress testing.

Any recommendations or best practices from Nordic or the community would be greatly appreciated.

[Samruddhi Jadhav]

Hi,

1) When selecting external antenna, ensure that it is 50 ohms at 2.4GHz. This is because the matching network and RF path on the DK are designed for a 50 ohms antenna port. You need this also for a proper RF layout. In case you want repeatable tests, make sure to keep the heigh and orientation of the antenna stable because moving it also changes the signal by many dB. The radiation isn't spread out equally in all directions. 

2) Any antenna which covers the band, so 2.4 GHz here, should be suitable. Our docs don't specifically mention using the Wi-Fi antenna but since BLE and Wi-Fi share the 2.4 GHz ISM band, the 2.4 GHz Wi-Fi antenna should be fine. 

3) There is no recommended antenna gain range however from Nordic's BLE range tests with nRF52840 DK, the on-board PCB antenna (low-gain antenna) was used. So, if you are looking for a similar behavior as BLE devices, you can use on-board antenna / external antenna with low gain. 

4)  One thing that you can be aware of is that increasing the gain also increases radiated power and range. Small changes in the direction of the antenna can lead to big RSSI changes so make sure they are pointed right so that the repeatability isn't affected. Check that your EIRP is within 2.4 GHz ISM limits. 

Best Regards,

Samruddhi

[PaKa]

Note that the connector on the DK is a SWF connector so you'll need a SWF-SMA cable and a SMA antenna.

The connector is not an uFL connector and uFL antennas/cables will not work at all.

Just mentioning as we have seen too many making this mistake.