External WiFi antenna for PCB - Gain vs. CE/FCC?

[Martin F]

Hi all,

We're looking at a couple of different WiFi antennas for our data logger.

For this purpose, we're using a WiFi chip which has been CE/FCC certified with an antenna with a gain of 2.2 dbi:
http://ww1.microchip.com/downloads/en/DeviceDoc/Acc-RN-SMA4-RP-DS.pdf


We've been looking at a few different antenna options, some with higher gain (3.0), approx the same (2.0) and lower (0-1).

Would love your input on:
1) In your experience, is it critical to choose an antenna with the same gain as the test for maintaining the CE/FCC compliance of the chip?
2) In your experience, how much difference does the gain make in terms of range in practical applications?

Thanks a lot!

Martin

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Some of the antennas we've considered:

3.0: https://www.aliexpress.com/store/product/1pcs-2-4Ghz-Zigbee-wifi-antenna-Small-pepper-module-aerial-SMA-male-rubber-antenna-PCI-U/2348143_32815899596.html?spm=a2g1y.12024536.productList_8241932.pic_2

2.0: https://www.aliexpress.com/store/product/1pcs-2-4Ghz-Antenna-SMA-male-3dbi-Zigbee-wifi-antenna-mini-short-rubber-aerial-SMA/2348143_32813612333.html?spm=a2g1y.12024536.productList_8241932.pic_16

0-1: https://www.alibaba.com/product-detail/2-4GHz-WLAN-WiFi-Bluetooth-11mm_60658569408.html?spm=a2700.7724838.2017115.554.219425ecDpD9Yc

[hagster]

I am not an expert in FCC regulations, but my general understanding is that the limit is on the maximum EIRP(radiated power). Generally this depends on duty cycle and usage.

Again, to the best of my knowledge, you can only get FCC certification on a complete system including antenna as it is the combination of radio output power and antenna gain that sets the max EIRP.

The RP-SMA came from a work around that allowed manufacturers to supply removable antennas so long as the connector was proprietary. Hence the Reverse SMA was born as simple non user swappable standard. Of course its now become a defacto standard and genric replacement antennas and connectors are common place which has totally made a mockery of the original regulation.

On the question does gain improve performance/range significantly. Yes it will...provided the gain is in the direction of the other end of the radio link. If the location of the two ends of the link can not be predicted, you are genrally better to have a low gain(but efficient) antenna. There can also be benifits of going with circular polarisation(like FPV guys do).

So I think you have 3 choices. Buy an FCC certified module(that will include an antenna). Or have your system certified with your chosen antenna. Or supply your product as a kit.

[angust_uk]

Hi Martin

I can't really help with 2 (other than to say antenna placement and layout is probably just as if not more critical than gain), but your first question is fairly difficult to answer due to the complexities of product certification!

As far as I'm aware, unless you're using a pre-certified module with a built-in antenna then you'll need to jump through all the certification hoops even if you use the same gain antenna as the chip specifies (there are so many factors that affect the actual radiation from the device that it needs to be fully re-qualified, which is an expensive process).

Also be aware that I think there are also extra rules if your antenna is removable. I'm afraid I can't elaborate much here but I'm sure someone else will be able to chime in with their experience!


Angus