I'm designing a 4-layer 6GHz RF PCB. The top layer is a signal layer and has the RF microstrip traces and the 2nd layer is an unbroken ground plane. I'm leaning against filling the remainder of the top layer with a ground plane stitched to the 2nd layer ground plane after reading a number of posts on this site indicating that it (1) isn't very useful when a full ground plane is used and (2) can create unintentional antennas. Additionally, since I'm using microstrips, I would need to keep the coplanar ground pour sufficiently far away which means that the total size of the copper pour would be significantly reduced.
However, I'd still like to use a via fence to prevent my microstrips acting like antennas and either disturbing nearby circuits or being disturbed by them. Are there any issues with using a via fence where the vias are not tied to a ground plane on the same layer as the microstrip? The vias would still, of course, be connected to the 2nd layer ground plane. I can't think of any reason why this would be an issue, and based on my understanding should be an equally effective EMI shield. Is this correct?
In a similar vein, is there any benefit to still keeping stitching vias in a \$\lambda/20\$ grid? The idea wouldn't be to stitch ground planes, but instead to act like a sort of general-purpose EM wave short for radiation from non-microstrip traces, or for any signals that managed to get through the microstrip via fence.