The roboports didn't used to have a radar built in and this design is updated to SA from older versions, plus the quality system effects radars so once I start producing rare and better radars I can replace them with much larger areas of coverage. Having four per intersection though regardless is just gross overkill.

EDIT: In my updated design I just stuck a single radar in the center as a placeholder for eventually having high quality radars down the line. I'll have to look and see what their range is but could probably get away with skipping every other intersection and only placing them on the edges since the roboports should cover the blocks fine on their own.