Antennas deal with the world outside the device. This would tend to indicate that they should be located on an outside layer.
While it’s easy to say that circuit board substrate material (woven Fiberglas with epoxy binder) is “transparent” to radio signals, a closer look reveals a dielectric constant of 4 as versus a dielectric constant of 1 for free space. This difference will have an effect on the behavior of the antenna (probably not much at 433 MHz), but it’s still not a good idea to bury the antenna under a layer of laminate.
Don’t locate any other conductors on layers below the antenna – just keep them clear.
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