Optional SMA Footprint

[chalecampb]

Hello,

I am basing a design on the reference design from the nRF-DK (pca10028?). I am trying to understand the implications of using an SMA connector footprint for testing purposes, but including a cuttable trace underneath the SMA connector making it optional.

First, my understanding is that while an antenna is not connected to the SMA connector, the terminals of the SMA connector are shorted. When a connector is added, it breaks the connection and connects the lead to the attached probe or antenna.

If this is correct, it should be possible to include an SMA footprint with an additional trace underneath, which should allow someone wishing to attach a network analyzer to the DUT to cut the trace and add the SMA connector (which would connect the trace again). Some questions,

1. Is this possible? Or is it only recommended to use either an SMA or only trace antenna, and not both?
2. What impedance should the trace underneath the connector be?
3. Is it possible to test the entire footprint and trace antenna in something like 4nec2, and does anyone have any examples for this?
4. Let's assume the trace is cut entirely between the terminals for the above questions (but not removed). Would the non-grounded trace existing under the SMA connector have any impact on the RF performance of the DUT?
5. I read on this post (devzone.nordicsemi.com/.../) that it was possible to send the design in for comment - is this still possible? I can post the layout for the area in question in this thread if it is easier, since the design is well known.

Thanks for any advice you could provide, I am still getting used to RF design considerations. -Alex

[chalecampb]

Should also point out that I have read both nWP-017 and the λ/4 printed monopole antenna for 2.45GHz document (thanks for those!). Neither mentioned the use of an SMA connector for testing if it would be left off during production.

[Øyvind Karlsen]

Hi Alex,

If you're thinking about the nRF51 development kit, the antenna is always there. There's a coaxial connector with switch being used, you can place a probe/cable into it and it will switch the signal path onto the connector, bypassing the antenna.

We found this to be an easy way to debug the development kit, it is possible to do what you're suggesting as well, but it will affect RF performance. If you're making a device I would recommend soldering onto the antenna output and cutting away the connection to the antenna.

You can definitely send in your design for review by our support team engineers, we also offer help with tuning. If you prefer you can post it here and we'll do our best to help you.

Best regards,

Øyvind