is there any study about the impact of cell sites on real estate value ?

Maybe you'll find something of interest or useful here

Burbank Action (Against Cell Towers in out Neighborhood)
Decreased Real Estate Value

I know of no such studies.  Most of the studies are on the health impacts.  And most of those tend to be biased toward industry, unless you look at a few long term studies from overseas.

Obviously, there is the visual appearance factor affecting vistas.  But the bigger concern of home buyers is potential health impacts.  And obviously, that depends both on distance, and how the antennas are aimed, and if you are in the path.

But with cell antennas being placed on the tops or sides of many commercial and institutional buildings now, you may have such antennas every 3 to 5 blocks!

I can identify over 25 different cell site locations in my city, and it certainly doesn't seem to impact the pricing nor the volume of sales any.  Most people never even ask.  Many don't even see the cell antennas when looking right at them.  Disguising them as palm trees and fir trees has helped some.

I still don't want my home located right next to one, even if it is under the signal path.