Why don’t fighter planes have 360 degree radar?
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Radar as we currently implement it requires a _phased array_ of small radar antennas. When you send radiation out from an antennae, depending on the design of the antennae, you get signal peaks and valleys. By using a computer to deliberately sequence or delay the signal being emitted from neighboring antennae in our array we can “steer the beam” by stacking the peaks together; this has the advantage of also minimizing the signal going off in other directions as well. Remember the downside to radar is you’re sending all this EM noise out into the ether and watching to see what it bounces off. It doesn’t take very complex electronics to triangulate where YOU are from the radar waves you send out. So phased arrays are good in that the only signal you detect from a phased array are when the radar is actively painting you (i.e. you’re about to receive a missile.)
The alternative is to use the old school rotating “send out a big wave of radar, listen for bounce backs.” method – like air traffic control radar or probably AWACS – there’s no point in hiding those systems. And they’re big and they rotate.
So if our fighter jet were to have beam steerable radar all around, you’d have to have these big flat phase arrays all over… and that would probably conflict with the design goal of making them fast and maneuverable. The _important_ role of radar is for targeting the bad guys – much easier to put that radar in the nose, but rely on dedicated AWACs radars to get you close enough and vector you to a shooting solution where you’re pointed at-ish the bad guys.
Keep in mind we can put radar _receivers_ or detectors all around our airplane – these just detect waves from radars that are painting us, and if you have a few antennae you can roughly triangulate where it is in relation to your plane.
Radar needs line of sight, more or less. The fuselage would block it, so you’d either need multiple dishes around the outside or have it protrude above or below the plane (or both, really) which would ruin their profile.
Radar antennas on a fighter plane are a bit like a searchlight; they are too large to just hang off of the outside of the fuselage without completely destroying the plane’s aerodynamics, and they don’t work if there is a piece of the plane in between the antenna and whatever they are trying to look at. These two factors make 360° radar on a fighter impossible; an antenna which can look in every direction will stick out so much that the fighter is uselessly slow.
You can look at aircraft like the E-2 Hawkeye or the E-3 Sentry to see the sorts of huge, drag inducing assemblies needed for 360° radar coverage; they aren’t necessary on fighters which can instead just radio a big AWACS plane for where the enemy is and then point their on radars in that direction.
So a fighter plane needs to be aerodynamic. This means a sleek shape.
Radar is given off by some sort of antennae. These are not sleek. To keep the sleek shape of a plane like a fighter plane the radar is inside the nose of the aircraft and so it just points forwards.
Another type of plane is an AWACS plane. You may have seen these. They have a massive radar dish on top of them to see everywhere. These planes can be large and cumbersome because they’re not supposed to get into dogfights and such. If you have one of these in the air its radar image can be transmitted to you either by just reporting contacts or actually some sort of data link that you can see.
Anyway, back to fighter planes. Fighter aircraft though do have smaller receivers on them. These are to detect radar waves hitting the aircraft so while the fighter plane may only be able to see what is in front of it from its own radar system it can detect if radar is hitting it from other directions and what type. So this will tell it if another fighter aircraft’s radar is looking in its direction (even further than that aircraft can detect it). It can tell the difference between a search radar and a lock on radar.
Now here’s the kicker. Fighter aircraft don’t always fly with their radar on. The reason, as mentioned above, is that your radar will be detectable at distances further than you can get a good enough return to see. It means that you’ll be telling everyone where you are before you can see them. So quite often fighter aircraft will just turn on their radar, see if anything is ahead of them and then turn it off and change their direction of flight. If they have their own AWACS up transmitting its radar to them then they might only turn on their own radar when it’s time to get a radar lock on a target. The side without an AWACS may have to be flying around with their own radars on more often and thus are actually at a huge disadvantage.
Just a fun note: the Su-34, a fast and maneuverable strike aircraft based on the Su-27 fighter, *does* have a rear radar. It’s the Russian equivalent to the F-15E Strike Eagle, more or less. The system is kept pretty secret so we don’t know how capable the rear radar is, but the main radars of the Flanker family have a 120° field of view. So it’s likely they cover a lot of available directions, although still not 360°.
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