nRFM9160 GSM antenna impedance

[borgestrand]

Hi, what is the impedance of the nRFM9160 GSM antenna?

I'm asking because I'm in the process of verifying the tuning on an antenna + LNA circuit. We will most likely tune by replacing the nRF9160 by an SMA plug and 50Ohm equipment. Can I connect this straight, or do I need a matching network to emulate the nRF9160 antenna input?

Best regards, 

Børge

[Andreas]

Hi Børge,

 

The antenna is approximately 50 ohms at frequencies for compatible bands, it is not perfect but max VSWR=3. Note that this will change in any other PCB, but can generally be adjusted by the matching as you say.The SMA plug or coaxial cable is simply connected in place for the missing nRF9160, no extra matching is needed. You might find this whitepaper handy, it is written with focus on 2.4 GHz antennas, but the general principle applies to LTE antennas as well: https://infocenter.nordicsemi.com/pdf/nwp_017.pdf?cp=14_13

 

Regarding the LNA though, are you planning to have an LNA on the LTE antenna? If so the nRF9160 will not like this, and would cease any nRF9160 protocol compliance. I strongly recommend against using any active devices externally on the LTE RF path, except switches for antenna matching. On the GPS antenna a LNA is fine and recommended.

 

Best regards,

Andreas