SWRA797 September 2024 CC1312PSIP
Each GND pad must have a GND via. However, this is difficult to follow when using just through-hole via technology due to the routing on the other layers. As can be seen in Figure 3-7 and Figure 3-8, the maximum GND via distance is approx. 1.5mm from each other for the GND vias that are in close-proximity of the CC1312PSIP.
1.5mm_max distance is based upon Faraday cage attenuation up to the 5th harmonic of 915MHz in a FR4 substrate with a dielectric constant of 4.5. Increasing the distance between the GND vias has less attenuation for the higher harmonics.
The distance between the GND vias is especially important for the 2-layer design since a 2-layer design inherently has less GND than a 4-layer design.