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PCB review and RF layout

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SierraFox:
Hello!
I'm working on a GNSS/GPS tracking device that will transmit its location on 915mhz to a handheld unit and I'm hoping I could get some advice on my PCB.
U1 is a microcontroller and the transceiver for the 915mhz channel. U2 is the GPS receiver. AE1 is a ceramic patch antenna connected to U2 via a U.FL connector.
U3 is a 3 volt LDO and U4 is a li-ion charger.
J2 is an SMA connector to connect a whip antenna for 915mhz.
J3 and J4 are the U.FL connectors.
The battery is going to be a AAA sized li-ion battery (10440)
The left and right halves are separate boards and the back view of the PCB is flipped. I also attached screenshots with and without the ground plane visible for clarity.
I feel like the layout is quite garbage, but I also don't know how to make it better. I also don't know much about layout for 1.5ghz signals. The RF traces are 0.8mm wide and have a clearance on either size of 0.15mm.
I would love some advice and please ask if you want more pictures or details.

aliarifat794:
Position the antenna (AE1) away from other components, especially noisy digital circuits, to minimize interference.

T3sl4co1l:
Seems okay.

May want more vias around the MCU. Can't quite tell which pins are ground, if any, but those should have vias near them.  Same for the GPS module; it has some nearby (including flanking the antenna trace, that's nice), but I don't know at a glance what connects where.

Don't know what the datasheet says, but the GPS module might want traces out from under it, you'll want to look that up.  You have tons of routing area to run traces around the outside, and stitch ground around the traces beside, so that's no problem.

What does the purple outline imply?  Is that a courtyard that nearby components should be outside of, or something?  I'm guessing not, as capacitors are within it.

Huh... is there no input bypass cap? Hard to tell without schematic, but it looks like that is the case.  The charger and regulator likely both would appreciate having such.  Beware of mechanical switching between large reservoirs (i.e. Li cell, ceramic capacitor), as inrush and voltage overshoot can occur; some series resistance (for a low-power device like this, even just an ohm in series with the switch might be adequate -- this does depend on the 915MHz radio's transmit power, mind), or a TVS at the regulator input, may be desirable.

Tim

tszaboo:
Download Saturn PCB toolkit, and enter that RF trace into the trace impedance calculator. You need 50 Ohm. I don't think you can get 50 Ohm on a two layer board with reasonable trace width. This is a coplanar waveguide for the calculations.

shapirus:

--- Quote from: tszaboo on April 24, 2024, 11:59:20 am ---Download Saturn PCB toolkit, and enter that RF trace into the trace impedance calculator. You need 50 Ohm. I don't think you can get 50 Ohm on a two layer board with reasonable trace width. This is a coplanar waveguide for the calculations.

--- End quote ---
That'll be about 1.6 mm (in a microstrip arrangement; CPWG will be narrower) on a 1 mm thick board IIRC. Looks doable, as long as we're speaking only about the trace that goes to the antenna: there's plenty of room for it.

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