nRF9160 External Antenna circuit modifications

RE: nRF9160 External Antenna circuit modifications

Michael — Fri, 17 Jan 2020 10:23:59 GMT

Very Informative - Thanks Andreas for your help and expert advise on this subject

Cheers

Michael

RE: nRF9160 External Antenna circuit modifications

Andreas — Fri, 17 Jan 2020 10:08:26 GMT

Hi Michael,

a) The configuration for the external antenna depends a bit on the external antenna you will be using.

Passive external antenna: You can do without an LNA (U3), but this will likely give you some performance boost. The need of a SAW filter depends on the isolation between the LTE antenna and the GPS antenna, and how much intermodulated emissions there are from the GPS antenna when the modem transmits. Some LNAs also have a filter built in, eliminating the need for a SAW filter. The schematic you snipped show a different solution, using RF switches instead to disconnect the GPS antenna when the GPS is not used.
Active internal antenna: Being active, this has a LNA built in and will give the best performance as the LNA is as close to the antenna as possible. You do not need an LNA on the PCB in this case, but will need a bias-T to supply the antenna LNA:

From DK v0.10.0:

b) Yes, this is possible, e.g. as done in our Thingy91:

This is not ideal though, it is hard to get a wideband enough antenna to support both LTE and GPS, at least PCB antenna, external might be easier. There is also a lot of loss between the antenna and LNA, meaning GPS performance will be further degraded.

You could also route the GPS signal to the ANT pin, out through the AUX pin and into the GPS pin. Description here: https://infocenter.nordicsemi.com/topic/nwp_033/WP/nwp_033/nwp_033_intro.html?cp=14_0

Last solution could be to find a 'N-in-1 antenna' that has separate connectors, but the antenna itself is one 'box'. There are probably a vast range of different types that support different bands, but this illustrates what I was thinking about: https://www.taoglas.com/product/adhesive-antenna-designed-for-use-on-metal/ They are probably relatively expensive, but this will probably give the best performance of all the same antenna alternatives.

Best regards,

Andreas

RE: nRF9160 External Antenna circuit modifications

Michael — Fri, 17 Jan 2020 08:48:04 GMT

Hi Andreas

Thanks for the information.

With regards to the GPS, initially I don't think I want to use the GPS connection - so as you say I can leave the pin floating.

Howvwer, If I did want to use it (for future proofing) what options are avaialable for use with an external antenna (due to me metal box)? By that I mean :

a) If I use an external antenna connected to the GPS port (via a UFL connector), what would the PCB hardware requirements be. I take it I will still need the QM14501 (LNA + SAW filter), and then leave out the RF switches (QM13132s) (while we are discussing these, may I ask why are there two RF switches (QM13132s) connected to the GPS and not one)?

b) I did hear some time ago that it may be possible to use the same RF antenna for GPS location (multiplexed)...... is this correct/possible??

Kind regards and thanks for the support.

Michael

RE: nRF9160 External Antenna circuit modifications

Andreas — Fri, 17 Jan 2020 07:30:23 GMT

Hi Michael,

You are correct, the highlighted items can be removed if you only want to use an external antenna. Note though that the connector in the DK is SWF, not UFL, and these are not compatible. For development or production testing, SWF is neat, but for products where the cable is to stay put for the entire lifetime of the product, this is not ideal as the cable tends to come off quite easily. UFL better with respect to this, the cable is not as easily detached, but it is not pass-through with no cable attached. Maybe a slight digression, just FYI so you choose compatible connector types all the way.

Not quite sure what you mean about the GPS connection. If you do not plan on using this you can remove everything from the nRF9160 GPS pin and towards the right, i.e.

The pin can just be left floating.

Best regards,

Andreas