Via-hole around the 50-ohm microstrip on PCB. What are they?

Hello,
I have noted that a chain of via-hole is present arount the 50-ohm micro-strips on the evaluation boards of amplifiers, mixers, etc.
I was wondering what they are and why they are needed.
Could you give me information? Are there a book o a white-paper on web that I can read to learn about them?
Many thanks.
Regards,

Antonio

Those are called a via fence. Look at this:
https://en.wikipedia.org/wiki/Via_fence

These lines aren't true micro strips but coplanar waveguides, using ground both on top and bottom side. Advantage is smaller line width, e.g. better matching to IC pin grid.

The impedance can be calculated e.g. with the Saturn PCB toolkit.

The "via fences" are there to keep the top side copper pours tightly connected to ground plane, otherwise they could form unwanted resonant structures.