vias on rf boards

some of the rf boards have vias on both sides of certain traces. what are the considerations taken in implementing, ie the size of the via, the number of them, separation between vias, separation between via and trace etc.

generally speaking the via is an inductance.
The value of the inductance is near 1 nH/mm
So the "path" from the critical components connections ( i.e. the source of the HEMT) to the ground should tale in account the lenght of the path.
For example to connect a source to GND lots of via should be placed around the source geometry.

Tha vias may by spaced by 5*H

An othe case, the back metallized coplanar waveduide, have lots of vias closest as possible to central line. as rule of thumb the spacing shoul be 3*H to 10 *H.