Rule of thumb to avoid coupling that might cause resonances in RF path:
Coupling is small if the distance is larger than 3*line width and larger than 3*thickness between signal layer and ground layer.
One thing that I can say for sure, UARTs have some of the noisiest buses from all digital circuits.
So staying with your RF lines away from them is mandatory.
From experience:
ok near transmitting antenna or LO output not ok near receiving antenna or mixer input/output traces - everything is amplified by mixer's opamp
I did a google search for "UART generated noise issues"
I´ve gon through the first 3 hits. All were about UART receiving noise, not sending out.
And even those issues were design issue, by letting the Rx floating or wrong wiring of a sitch mode motor control (noise source)
I did not look for more. ..
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Undoubtedly every digital signal sends out noise. So does UART. But I´m not aware that UART is worse than other interfaces.
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But as long as the OP does not give any useful informations the thread is rather useless.