Radar · 4:11am Nov 15th, 2013
Well, I guess I've committed myself to blogging about weapons systems. Can't have most of them without radar, so let's get this out of the way now.
Your grandparents think this is funny.
Most of you probably understand that radar is a device that lets us detect airplanes, ships, and other stuff by bouncing signals off them. While that's true, there's so much more to know.
The basics: The radar system sends out a pulse of energy. That goes out into the atmosphere until it hits something and then comes back to the antenna. Because radio waves move at the speed of light and we know that speed (299,792,458 meters per second), the radar can time how long it takes for the echo to come back and that tells us how far away the object is.
RADAR = RAdio Detection And Ranging. Basically, it detects stuff and tells us how far away it is. It uses radio waves. The frequency of the waves depends on what the radar system is and what it does. Generally, lower frequencies are used for longer ranges. Higher frequencies can't go as far, but they are generally more accurate because they have greater resolution. Basically, the higher frequency can carry more information, providing a sharper image like a screen with more pixels.
This is a mechanically scanned radar. This is a basic ASR-9 system in use at many airports. It's probably what you think of when someone says radar: that spinning dish thing. It makes sense for the dish to spin - that way it can see everything around it with 360 degrees of coverage.
Here we see the SPY-1D phased array radar aboard an Arleigh Burke-class destroyer. Those flat panels that the arrows are pointing to don't spin. They don't move at all. The ship has two more to cover the rear. The four panels together can see everything around the ship.
Phased array requires a little more explanation. Each panel has many smaller modules on it that work together to form the radar beam. The previously mentioned SPY-1D has something like 4,000 modules per panel. Despite being a flat panel, phased array can "steer" the radar beam around. That's how four stationary panels can cover 360 degrees. The advantages of phased array over mechanical scanning are many. It has no moving parts so it's more reliable. It's also faster, not having to wait for the radar dish to spin around. Unfortunately, it's more expensive and the electronics to run it are much more complicated.
Can't afford multiple panels to get full coverage? Just mount one panel and spin it around, like this Russian FLAP LID radar.
Many new warships and fighter jets are getting phased array radar. There are two major kinds of phased array: Passive Electronically Scanned Array (PESA) and Active Electronically Scanned Array (AESA). Both kinds have their panels covered with modules, but AESA powers each module independently, while PESA powers them all from one central source. PESA is easier to build, but generally AESA is the better design.
The APG-79 AESA radar from a F/A-18 E/F Super Hornet. You can see all the little modules on the surface. It has cool capabilities like SAR (synthetic aperture radar) imaging. Basically, it can produce radar beams so fine that it can pretty much take pictures of things, even on the ground.
SAR image of U.S. Capitol
Clearly, radar is an important thing to have. The next question is, how can we keep the bad guys from having it? We use jamming. This can be either electronic or mechanical.
Mechanical jamming is the use of decoys to confuse the radar. This includes chaff, a cloud of little pieces of metal that look like something big on the radar screen.
To electronically jam a radar, you have to broadcast a signal that is similar to what the radar is using. Your signal is supposed to block the radar from hearing the echo from the pulse it put out. There are a lot of techniques for going about this, and some radars have counter measures like shifting frequencies to compensate. The overall rule is that your jamming signal has to be more powerful than the echo so the radar won't be able to detect the echo.
Obviously, if you're dealing with a powerful radar, this is more difficult. Good 'ol SPY-1 is generally advertised to put out about six million watts of power. However, at very long ranges when signals grow faint, jamming can be used. The closer you get to a radar, the harder it is to jam and at some point if you keep approaching, the radar will "burn through" the jamming.
You can also transmit false signals to a radar so it isn't sure whether your signal or its echo is the correct return. This can cause you to look like more than one target.
There are a whole lot of other effects out there, like how weather can affect radar. You can also, under the right conditions, bounce radar off the ionosphere for longer range. That's beyond the basic lesson of this blog, however.
I'll leave you with an image of one of the largest radars in the world, the US's Sea-based X-band Radar, used as part of the Ballistic Missile Defense System. It has a listed range of more than 1200 miles.
I laughed at the first picture.....
M.A.S.H. is funny
Wow. That last one is gigantic. For some reason, this angle makes it look like it is prone to falling over.
1508893 When it's not being transported by ship, it sits lower in the water.
mda.mil/global/images/system/sbx/img_2845.jpg
1508899
Holy ship, that thing is awesome.
Very informative stuff about radars!
Gotta love the work that Dockwise accomplishes.
I love Radar! That guy made that show!
You should make a crossover with MASH.
I knew the basics of how radar works, but some of the more advanced stuff, like the different systems, was actually very interesting.
Electronic jamming could be explained as being like shining a flashlight or laser pointer into someones' eyes to blind them.
But your post, while showing more knowledge than I have on the details of radar systems, did leave out a third approach to defeating radar systems: design & materials to reduce an aircraft's radar return.
Materials that either absorb radio waves completely, or let most of them through, are harder to detect with radar systems. On top of that, properly shaped planes (avoiding things like a sharp 90° between surfaces) can avoid retroreflection issues, and make for a weaker radar signal return.
1508899
......now it looks like a giant nipple. Jeez, what's wrong with me.
Informative as always sir!
I feel old for laughin' at that MASH joke.
I did too. my dad has a shirt with that, custom made by yours truly in class.
I'd also like to point out, simply for consistency's sake, that Radar speed detection works by double-tapping, then calculating the difference in return times.
The more you know!
Don't forget that so-called stealth aircraft aren't invisible to radar. They just produce a much smaller radar reflection (in some cases as small as a marble or golf ball IIRC) through a combination of precise shaping and specialized materials.
You should have pointed out the difference between passive and active radar.
Choppers, incoming
There was this (old) Navy video I saw that explained how the enemy can detect you with out using their RADAR. All thay needed is a radio/electronic signal dector (i dont remember). Basically, if your group has all their RADAR blaring, it sends out so much electrical power that if the enemy has this device, they can pick where the signal, you, is coming from. Before your RADAR see them
If I find the video, I will link it
2256408
Completely correct. Basic direction finding equipment can help, but more advanced things can tell exactly where an electronic emitter is. Super cool advanced stuff like specific emitter identification can even tell you what it is, right down to the exact ship.