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.
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)?
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.
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.
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.
Maybe the LOLIN C3 Pico?
Ooh, nice! Thank you, that looks great and only a tiny bit bigger, it also has a JST which is great.
- no, this is fine, you can find it in routers all the time (usually with printed antennas, or wire antennas)
- 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
- 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 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
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
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.
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)
This all seems really complicated but at the same time super interesting. Thanks for the recommendation.
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
i don’t know what are you looking for so i’m just gonna drop some resources that i’ve used:
starter: https://www.antenna-theory.com/antennas/main.php
more comprehensive: https://www.microwaves101.com/encyclopedias
and on top of that, various amateur radio pages, some are indexed in dxzone.com
there seem to be two hard limits on antennas in general. one is for approx lossless antennas that are large compared to wavelength: gain, beamwidth and size are related through diffractive limit https://en.wikipedia.org/wiki/Diffraction-limited_system it’s really about capture area, which is intuitive for things like parabolic reflectors, but for things like yagi antennas there’s some defined capture area that ultimately depends on their length
the other one is on non-directional antennas that are small compared to wavelength. basically one good antenna that you can make is halfwave dipole, you can try various trickery to make it smaller, but this comes at a cost of either smaller bandwidth or increased losses, or both to lesser degree. it might make sense to make an antenna with 70% efficiency which is 3x smaller for example. it all depends on precise requirements
at the end of the day the most important material in any antenna are tradeoffs
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.
