How to improve the antenna signal

[Jet Hua]

We have connected a 50 Ohm Antenna with NRF52832-QFAA-R7, but we tested and found the antenna signal is weak. Could anyone help to provide some proposals for how to improve it? Thanks in advance.

[cbd]

There's not much information to go on e.g. what chip antenna are you using?

First questions that come to mind are:

• Is the chip antenna correct for the frequency?
• Is the chip antenna placement and tracking correct?
• Has choice of track width and spacing for the antenna compromised the overall chip to antenna impedance?

And finally, this is where antenna tuning, by transmitting a carrier wave of know frequency and strength then changing those tuning components comes in.

[awneil]

Jet Hua said:

we tested and found the antenna signal is weak

How, exactly, did you "test" ?

What results did you get?

What were you expecting?

https://devzone.nordicsemi.com/f/nordic-q-a/48284/nrf52832-wlcsp-ciaa-rf-do-not-work/191537#191537

https://devzone.nordicsemi.com/f/nordic-q-a/48816/regarding-the-schematics-of-the-nrf52/193876#193876

[Andreas]

Hi,

 

The main suspect is the antenna, even if the datasheet and manufacturer claims 50 ohm, this is usually only the case for the evaluation board which the matching components(MC8, ML7 and MC12) are valid for. When placed in your PCB, these need to be updated. The more your board deviates in size and shape from the evaluation board, the further 'off' the default values will be. You should also replicate the mounting position and nearby layout and keepout that is specified by the manufacturer to ease the tuning. See this whitepaper: https://infocenter.nordicsemi.com/pdf/nwp_017.pdf?cp=12_11

There are a couple other issues with the design that most likely do not help, but probably not as much as the antenna:

• Our reference layout is not very well replicated, C10, L3 and MC9 probably need to be re-optimized to make up for the lost performance. 
• Signal trace underneath the RF path, there should be solid ground only.

 

I would probably redo the layout and get it right from the beginning rather wasting time trying to get this to work. If you register a private case we are happy to review your design and suggest changes before you gerber out, or test/optimize the boards once you get them back.

 

Best regards,

Andreas

[awneil]

Andreas said:

redo the layout and get it right from the beginning

Or use a module - which takes care of all this stuff for you!

See earlier links.

[cbd]

All typical issues. +1 Andreas

Even using the same layout may trip you up if the reference board is 1.6mm two layer and you're using 0.8mm 4 layer!

As Andreas points out you have a signal line passing under the antenna trace, which is a big no-no.

Judging by the pad sizes on the antenna trace and in comparison with the MCU pad sizes I'd also say that it's too narrow and so your base impedance is too high and once your tuning components are placed the total is way more than what you want.