To pass the EMC test, it is first necessary to ensure that all signal lines are laid on the same side as much as possible. If this can be achieved, then the other side can be used as a continuous ground reference plane. However, if it is necessary to switch signals between layers through vias, as in this case, these vias should be made as short as possible.
For example, a signal starts from the top layer, goes down to the bottom layer through a via, and then returns to the top layer through another via to continue the wiring. When making such a layer switch, don't forget to place a return via next to it to provide a continuous return path for the signal.
After designing in this way, if the bottom layer is used as the ground plane, the ground plane split caused by the vias will be very small. Although such a double-sided board design may not be perfect, as long as the layout is reasonable and the return path is complete, it is usually sufficient to pass the conventional EMC test standards.