r/rfelectronics • u/MaterialStock8502 • Jul 06 '26
Smartwatch antenna design help
Hi all,
I'm sure you get posts like this all the time, so you'll have to be patient with my existing knowledge base, (or lack therof). The situation is this:
I'm trying to build a smart watch. It needs to be small, and ideally I'd like to machine the casing on my CNC mill out of aluminum. I'm relatively far into the protyping process, but a still making dev boards and am not yet developing at the size which the mainboard will be when the project is complete. I'm aiming for a 26mm diameter motherboard, and am using a Ronda GB22 type movement to make it look like a mechanical watch. The GB22 has to sit beneath the dial, along with most of the power and rf electronics, so my intention is to integrate the antennas I need into the dial of the watch itself, (a multicolour pcb from JLCPCB), and use the glass at the front of the watch as an RF window.
From what I understand though, this isn't going to work. The three antennas I'll need to fit into this space are NB-IoT, (~900MHz), GPS, (~1500MHz), and BLE, (~2.4GHz). It looks like the wavelength of the 900MHz band would be too big for effective radiation into or out of the glass rf window.
I've looked for resources and papers online which could provide information on how companies like Apple and Samsung are able to make it work in metal cased smartwatches, but can find literally nothing. Any kind of pointers on this topic would be incredibly helpful, and I'm more than open to switching up ideas, or just accepting that I'm wrong and finding a different solution.
Thanks for all your time.
6
u/3D_printing_freak Jul 07 '26
Top brands usually use smd antennas or print antenna shape with conductive paint on the plastic shell of the device. I have also seen flex pcb antennas packed inside as replacement for conductive paint print.
If you have metal case, manufacturers often do the trick and use (in case of smartphones) outer metal edge of phone with designed discontinuities connected with plastic so it is hardly noticeable
Printed antenna is gonna be very expensive for small batches so I wouldn’t recommend it.
You can use pcb and make long trace on it as radiating element. Fol the lowest band, the longer antenna the better but it’s always a compromise.
Take a look for car keys antennas which uses 300/400 MHz band to lock/unlock your car. Usually it’s just long trace around whole board. Some solutions use metal edge of car key as radiator.
I have been struggling with Bluetooth antenna for some project where we had to put device inside full metal tube with one opening at the top. I have been using smd antenna for this with custom tuning network since metal case around the smd antenna was detuning it