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Some advice on creating a 2.4 GHz antenna for Seeed ESP32-C3 (lemmy.blahaj.zone)
submitted 1 year ago* (last edited 1 year ago) by KyuubiNoKitsune@lemmy.blahaj.zone to c/askelectronics@discuss.tchncs.de
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Hi,

I'm looking for some help in a field that is super technical and I don't fully understand.

I'm planning on using a bunch of these seeed studio Esp modules for some home automation projects, especially because they have a lipo battery charger making it great for portable stuff.

The thing is the the ESP32s have U.FL SMD antenna connectors. Most of the antennas that you can buy with U.FL connections while are reasonably small, come with 50-150mm leads, which sort of makes the small size of the module a little less valid.

What I'd like to do is get a female U.FL SMD connector and make a small daugherboard with an 2.4GHz SMD antenna on it, for instance a Janson 2450AT42B100 or a Molex 479480001.

They go over the circuit board requirements quite thoroughly so I don't think designing it will be too difficult, but what I don't know is, they say that you need impedance matching on the circuit, and I see that there appears to be something that looks like it on the ESP circuit diagram, but I'm not actually sure if it is or not:

You can see it in the middle near the bottom of the diagram here: Seeeduino-XIAO-ESP32C3-SCH

So my questions are:

1: Is this a dumb idea, having a direct plug-on SMD antenna?

2: Is that an impedance matchning circuit between LNA_IN on the ESP chip and U.FL-R-SMT-1?

3: If I can't get a female U.FL SMD connector, would using one with a lead and shortening it to make the daughterboard able to be much closer to the connector affect anything? Do I need to ensure that the lead length matches the wavelength at all?

Edit: Found this SMD female U.FL, so they do exist.

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[–] skillissuer@discuss.tchncs.de 3 points 1 year ago* (last edited 1 year ago) (2 children)
  1. no, this is fine, you can find it in routers all the time (usually with printed antennas, or wire antennas)
  2. so it seems, however remember that at microwave frequencies you might start seeing distributed elements as a part of matching circuit (patches, open or shorted transmission lines etc) every fraction of mm is critical. i don't know what impedance gets this thing on output, but it might be very well non-real. it's usually done so that everything is matched to 50 ohms
  3. assuming that output is matched to 50 ohm, which is usually the case, you can use any length of coax, as long as losses don't kick in too badly. this means you also have to make your antenna 50 ohms. i see you're using ceramic antenna, which provides matching circuit for you, but there are other options like inverted-F antenna (3cm long) or even smaller zigzagged *inverted F antenna or halo antennas (some 2cm dia), which would require matching. tradeoff is better efficiency (less heating; one of these antennas wastes almost 40% of power) and the fact that you can make them on your own
[–] skillissuer@discuss.tchncs.de 3 points 1 year ago* (last edited 1 year ago)

antenna design is usually limited by one of these things: size, gain/radiation pattern, efficiency, bandwidth (fixed here, entire 2.4ghz band)

you can probably use off the shelf antennas used for drones if these are small enough for your application

soldering coax can be tricky, don't melt center insulation. you'll need to size microstrip line so that it'll have impedance 50 ohms as well https://www.pasternack.com/t-calculator-microstrip.aspx

[–] KyuubiNoKitsune@lemmy.blahaj.zone 1 points 1 year ago (1 children)

Thank you for your detailed reply, I really appreciate it. It answers my question and raises a whole bunch more :D, I think I need to brush up on general RF and get a better understanding of how it actually works. I shall do some youtubing and reading on it. I found a really good pdf that discussed antenna design but a lot of it I didn't understand, so I'm going to need to learn a bit more.

Ill also take a look at the drone antennas too.

Thanks again for your help.

[–] skillissuer@discuss.tchncs.de 2 points 1 year ago (1 children)

if you want to measure anything rf, you'll need a vector network analyzer like nanoVNA (some $40), this will be very useful in tuning/matching antennas (and making sure you won't get reflections that could potentially damage transmitter if you screw up badly enough)

[–] KyuubiNoKitsune@lemmy.blahaj.zone 1 points 1 year ago

This all seems really complicated but at the same time super interesting. Thanks for the recommendation.

[–] M_Reimer@lemmy.world 1 points 1 year ago* (last edited 1 year ago)
[–] abs_solution@discuss.tchncs.de 1 points 1 year ago (1 children)

I have no concrete answer to your post...

However I would be interested to know where I can earn more abt the topic of electronics, I am very interested in learning it and it would be nice to get some guidance. ty in advance

[–] KyuubiNoKitsune@lemmy.blahaj.zone 1 points 1 year ago

I.. Don't actually know, I've just cobbled together information over the years. My dad worked in an electronics workshop but never taught me anything. There's a good intro to electronics course on udemy and if you're serious about it, try get the book The Art of Electronics, its like an electronics bible.

[–] elmicha@feddit.de 1 points 1 year ago (1 children)

Is this not the same ESP32 with an antenna? Although I don't know how the nRF52840 from your question comes into play here. Don't you normally use an ESP or an NRF, and not both at the same place (with the exception of a gateway maybe)?

[–] KyuubiNoKitsune@lemmy.blahaj.zone 1 points 1 year ago (1 children)

The nRF was a useless inclusion tbh, sorry for the confusion. The nRF already has an smd antenna.

The thing with those antennas is the size of the antenna vs the size of the module, it's almost twice the size, negating any benefit of having such a small module.

Hence my desire to use an SMD antenna on a small board instead.

[–] elmicha@feddit.de 2 points 1 year ago (1 children)

So you have these boards already? Or could you just get other boards with an ESP32 and LiPo charger? Because many already have a printed or ceramic antenna built-in.

[–] KyuubiNoKitsune@lemmy.blahaj.zone 1 points 1 year ago (1 children)

I do not. I'm planning on it though.

Do you know of others with charge controllers with that from factor? The only one close to it I've found is the is the m5stack m5stamp, but it doesn't have a charge controller.

I don't mind creating the daughter board, I think it could be fun.

[–] elmicha@feddit.de 2 points 1 year ago (1 children)

Maybe the LOLIN C3 Pico?

[–] KyuubiNoKitsune@lemmy.blahaj.zone 1 points 1 year ago

Ooh, nice! Thank you, that looks great and only a tiny bit bigger, it also has a JST which is great.