Nowadays you may see any target in 360 degree sector. It is not realistic model.
Make something like that, please: http://i.imgur.com/rKmeF5n.png
So you may see targets on the radar only in small sector ~ 60 degrees.

UPDATE (16.10.2014):
There will be Helicopter DLC published soon. Probably, it is a good moment to implement new radar system not only to helicopters but any other aircrafts + AA-tanks. Here is some photos from RL (they are for meteorogical radar, but display the main principles of radar system):
http://avstop.com/news/radarsector_avi.gif [^] [^]
http://sarasotaavionics.com/images/images/gwx70(4).jpg [^] [^]
http://www.flightsafety.com/elearning/fs_el_assets/courses/weatherradar/img2.jpg [^] [^]

And for AA-tanks:
http://vestiprim.ru/uploads/posts/2014-05/1399523488_aviaradar.jpg [^] [^]
http://www.theenergyworkshop.co.uk/images/Aviation-3.jpg [^] [^]

So there are several improvements:

1. Decrease angle of radar on all aircrafts (but not compass).
2. Add visual refresh of targets like here: http://avstop.com/news/radarsector_avi.gif [^]
3. Make 360 angle radar for AA-tanks with refresh function, for the whole 360 degrees, like here: http://vestiprim.ru/uploads/posts/2014-05/1399523488_aviaradar.jpg [^]

Here is youtube videos (to show main principle for both AA-tanks and aircrafts): http://www.youtube.com/watch?v=i5XTkjyZVaM (intensity of color of targets changes in periods between target refresh). And here is meteorogical radar: http://www.youtube.com/watch?v=NEWtxevbqYc

Also it will be good to implement radar sound system (beep sound) when your radar finds enemy, something like here, but not so frequent and only when radar refreshes: http://www.youtube.com/watch?v=aM_jlBwoS2s

This kind of radar will give much more immersion into the game. I don't ask you to implement all of this things but decrease of the angle is main. Nowadays, radar system in game is too arcade.