From: Leeuwarden, Netherlands
Funny you should mention that - I've been considering coastal bunkers and flak towers as well. In fact, these locationtypes would be easier to build than radar installations.
How to actually make radar work within the current game architecture would be to buy research that either 1) enables the player to upgrade his planes with better spotting, range, and kill ratios, or 2) have the research trigger an event that "mutates" or "morphs" existing units to improved models, with higher spotting/range/kill ratio. Can't recall the exact coding, will need to look in the editor.
If I had better coding skills, I could build more effects/variables into locationtypes. Instead, any simulation of improved radar is going to have to be executed via subformationtypes.
One could argue that bunkers placed at a coastal line would be "coastal bunkers" and that Flak units would act as "Flak towers"... but still I feel it would make more sense - map wise - to be able to build these structures on the map. Coastal bunkers and Flak towers could be upgradeable, from 1 to 4, better guns and more hitpoints.