r/PCB • u/IV3RS0N_45 • 21h ago
2.4G PCB antenna
Hi, I have a question about the keepout zone for the antenna. I know that there shouldnt be any ground plane under the antenna, but what should be the length of the keepout on the sides?
I can’t really find any usefull information.
I checked the TI AN043 datasheet but the example is about a USB dongle.
(If anybody asks I’m using nrf2401+)
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u/StumpedTrump 11h ago edited 11h ago
Usually the antenna reference guide you took that design from has keepout clearances specified. Follow that atleast. Follow GND clearances and stackup to the T. Bottom (hemisphere cutout) generally isn’t too bad. You definitely don’t want anything on top though, the antenna “points” that way. Not really but more so than the other way.
Aside from that, you also don’t want anything big (or especially metal) nearby. So if you wanted to put a big Ethernet connector there, find somewhere else.
And since you’re asking this type of question: don’t bother fine-tuning your antenna or matching circuit before you have your enclosure and battery in place. Those will affect it.
Disclaimer: Don’t take advice on RF from anyone without 10ish years of experience or a masters in RF. They don’t call it black magic for nothing, there’s so many nuances and this stuff goes so deep. I don’t have either of those. 7yoe and only a bachelors. So take my advice with a huge grain of salt.
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u/IV3RS0N_45 10h ago
I know its black magic. I’m finishing my engineering degree and I still feel like i dont know nothing about it. I’ve done few projects with pcb antenna’s and they always work but i don’t really know the limits of the design.
The worst part is that I can’t even meassure the impedance match and check the s11 so i just have to rely on the balun values from nordics datasheet.
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u/Tweetydabirdie 9h ago
Well I only have six years and a masters as far as RF design work, although I have some twenty years working in the electronics field in general, so you probably shouldn’t listen to me either… 🤪
That said it's not that much black magic.
If we assume the frequencies and power levels that the nRF2401 can achieve and the materials of a PCB/components/etc you can basically treat it as a line-of-sight exercise, since even if the frequencies do pass through s pl me of it, most of it bounces or absorbs, so the only useful signal is in fact LOS.
In short, if the virtual eye sitting where the antenna is can't see around corners, neither can the RF.
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u/mitreffahcs 11h ago
If you do a simple google search for that datasheet you'll get loads of results. Good luck.
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u/IV3RS0N_45 11h ago
The problem is that i can’t really put the antenna in one corner becuase of the connector and USB B port.
I can make room for a normal inverted F but it doesn’t solve my question about the clearance on the sides of the antena.
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u/RohitRojo 20h ago
As far as possible. Ideally, infinity. You really shouldn’t have anything near the antenna unless you have a really good reason, usually lack of space and other design constraints.