Updated Version of https://mods.factorio.com/mod/RadarGridGuide (copying description from there. I don't take any credit for this. I just Updated it for 1.0)
I forked this on the original github of the mod and the link is provided as the "source"

This mod adds a visual indication to the world to help place radars on a neat grid.

To reposition the guide marks to match an existing radar setup, or reconfigure for a modded radar with non-standard range, hover the mouse cursor over a radar and press Control+G

To show or hide the radar placement guides, press Control-G (with no radar under the cursor) to toggle the mode.

NOTE: This mod may not work - and isn't that useful - with mods that add many upgradable radar levels to the game. If you want longer range radars, stick with mods that change the default radar range, or those that just add a small number of radar upgrades.

Release Notes
v1.0.0 - update for Factorio 1.0.x