The real problem comes if you have limited power and you can’t readily detect your signal. It’s how the RF propagates through the atmosphere that makes detection hard. First, you need to have a receiver with sufficient sensitivity to receive the signal. Then you have to account for how much power in the signal is lost during its propagation. You lose power through propagation first as the RF travels out to the target. And then again on its return trip to the receiver after it reflects off a surface. Range in this context is tied to power. This math is not as easy as the simple time and direction I mentioned above. So we need an equation, and thus, the radar range equation was born to the peril of many electrical engineering students. It’s not actually a range equation, it’s a power equation. For it to work, you have to have a receiver sensitive enough to receive the power that you transmit after it is reflected back to you. If all the power transmitted is reflected, you need only a few terms to figure shit out. Power at the receiver (when the energy returns) is equal to the Power Transmitted (PT) divided by 4 x PI^2 x R^2 (range out to the target) x R^2 (range back to the receiver). PR = PT / (4 x PI^2 x R^2 x R^2).
I know what you are thinking, and this is why I don’t do math for a living. Why do we multiply the R^2 term out to the target with the R^2 term back to the receiver, yielding a total power loss of R^4 for this propagation? If the power propagates over a distance, why wouldn’t we simply multiply by two, because the range is increased by twice the distance? This would yield the term (2R)^2 versus R^4 right? Again, this is why I don’t do math. Try this at home if you want to…but don’t tell anyone lest you trifle with all the engineers that came before you who couldn’t figure it out. I think it’s empirical. They measured it and came up with the equation. Radar engineers will tell you it has something to do with the isotropic radiation of a sphere in all directions...but that still makes no sense. The energy isn't reborn. It's continuously traveling over a distance out and back.
But, as stated, you don’t ever have enough power, primarily because of the R^4 term. So you have to consider the power you do have with all the crazy shit that is also in the environment. You need a directional antenna to focus your power. You need to hope you reflect off a large aircraft…not true if your adversary knows how to screw with their own radar cross section or RCS. This abstract measurement is the estimated reflective surface loosely attached to the shape of the reflecting aircraft, usually estimated as a two dimensional plane or the flat surface area. In my estimation, they kind of made it up. Again, to really know it’s empirical, you have to actually measure it.
Another confounding problem is the RF that is already in the environment such as from actual communications devices, or your own reflections off of immovable objects that reflect, such as mountains and buildings--this is called clutter--since they needed yet another term for noise. Then you need to include the temperature of the strange RF in the environment coming from the background of the cosmos that followed the big bang. WTF? Why? We are not even sure there was a big bang. As with the strange nonsensical math above, I’m not going to address that here. Sometimes I think those scientists that invented radar at Tuxedo Park were really just drinking whiskey and screwing each other's wives.
If you can do all this you can determine if something is there…you have achieved the detection of reflected energy. One blip. One blip Vasyli, one blip only--That’s different but strangely the same. So from this one blip, you know two things. You have a very certain direction and you have a range to target. You are in the game, but just barely. And, if it keeps reflecting as it moves, you are winning a bit more. But there is no chicken dinner. You can begin to track that reflection as it progresses and begin to give it other attributes. Maybe you can determine its direction of travel, perhaps figure out its velocity, and typically, though somewhat harder, you could figure out its altitude. If the amount of reflected energy increases, for a given range, you might be able to deduce something about its size. Big aircraft reflect more energy, in theory. You cannot, however, determine if the aircraft is friendly or hostile. It’s not something you can measure with a pulse of energy--although many have foolishly tried.
This leads us to the first Disadvantage of Radar. Or Disadvantage #1. The main disadvantage of radar is that once you know something is there, in order to do something about it, other than track it, you will require a whole lot more information. And you will need that information continuously. In military parlance, after you find the aircraft you will have to fix and target it. Typically you will bring in several more sensors in order to accomplish this part of the kill chain. So, Disadvantage #1, is that you can’t go it alone. You need help. At most, you have an indication. Call it, an early warning, because that’s what it’s actually called. Then you have to call in the calvary. Something has to get a higher fidelity look…and then many more frequent looks, if you want to do something about it. Before I focus on how truly disadvantaged and debilitating Disadvantage #1 is to air defense, I’d like to talk about the other disappointing disadvantages of radar.
Disadvantage #2 is far more insidious because you can easily be fooled into believing a lot of things that are simply not true when using radar and you discover a blip. Those things can be a result of problems with your radar’s own signal processing…or as a result of the adversary doing something nefarious to fool your radar. Opportunities here are endless. False alarms are also endless. But the main thing I want to discuss is just how sparse the information you do have can actually be. It’s tiny. In an ocean of sky you have a blip, or dot (it's the actual skin return) of energy every few seconds depending on the revisit rate of your radar. It’s not a picture, it's got no resolution, you can’t derive shape or size or depth. Without some sort of additional assistance you can’t even figure out the altitude. All you have is a direction and a range at most every few seconds.
When you try to add other information you are plunged directly into the world of sensor fusion. That’s something the human brain does extremely well…but something that is extremely difficult to automate with math. Animals in general have all evolved to have incredibly good sensor fusion depending on their chosen forms of sense. In sports, we all know the phrase when a player blows it because they sensed the opposing player is very close and about to make a hard tackle, ”They heard the footsteps”. Maybe they heard them, or maybe they actually felt them as the pounding footsteps got close…but the bottom-line is that those other senses entered the fusion equation in the human brain and a reaction resulted…good or bad. The good case may be, in American Football, you braced for impact and held on tighter to the ball. In European Football, you leap into the air to jump over the slide tackle coming in from your blind side. Radar can't hear, see, smell, or feel the vibration as one might do with multiple phenomenology's. So we strive, in modern air defense systems, to add as much additional sensing to the environment that is practical. For air traffic control, we have all but eliminated radars in favor of the air traffic simply telling us where they are. ADS-B is a requirement for most commercial aircraft these days. The aircraft knows where it is, so it beacons out all of the information necessary for air traffic controllers to track their whereabouts. The problem with ADS-B is that it’s a peacetime solution. You can now do this yourself, if you need to know where all the aircraft are, if you are out flying (or driving) in your car. Check out FlightRadar24. You’ve got your own radar for the world. Except it’s not radar…it's all ADS-B reporting. In wartime, expect everything to go silent. You would never approach an adversary's airspace shouting out your approach. “Here I am, Here I am”. Yeah, not a good idea.
Is there a solution? Why can we see so well with our eyes while radar sucks? Answer one, is God. Millions of years of evolution to create the Mark I eyeball with attached sensor fusion. Answer 2 is, of course, the Sun. And God said, “Let there be light”. I guess light came first, before the eyeball. In the case of our eyes, at least during daylight, the radar transmitter (or electromagnetic radiation transmitter) is the Sun. A freaking star using nuclear fusion to produce a billion gigawatts of energy in many parts of the spectrum, all streaming to Earth at the speed of light. So much energy that if we didn’t have an ozone layer we would all be fried eggs.
Fighter pilots can use their Mark I Eyeball, on a sunny day, to see and track down their adversary. They can also use the sun to shield their arrival. Fly out of the sun, with the sun at your back, and the sun jams your adversary’s Mark I Eyeball. But we don’t need to use our eyes, we can build electro-optical sensors to see…the sun is still a problem for anything that senses visible light. As are clouds. And of course darkness. If you really want to attack, attack at night. “They mostly come at night. Mostly “. But should you wish to go with visible, or even see with infra-red radiation in order to get greater and greater range with these systems, it requires building bigger optics. These systems tend to weigh more. Lenses, typically made of glass, are heavy AF. Think telescope. And they are almost impossible to point in the right direction. Think about finding your girl friend across the table by looking through a drinking straw. If you’ve ever done any backyard astronomy you know how ridiculously hard it is to point a telescope.
Disadvantage #3 is that RF requires a physical antenna, tuned to the frequency that is being transmitted or received. The physical antenna has to exhibit some sort of behavior that can be measured when in the presence of the RF it is tuned to detect. Typically that behavior is simply to shed electrons in unison with the RF wave that is propagating through it. In unison means at the same frequency of the RF wave and with a proportional level of power depending on the amplitude of the wave passing through it. This means, if you are going to use radar to your advantage, across numerous frequencies, even though you might process the blips of information exactly the same, to create them you need a different transmit antenna and receiver antenna depending on your radio frequency. For most military applications that’s probably three to five different physical antennas to cover the spectrum. That just sucks. That’s just life.
Disadvantage #4 is that due to the wisdom of the US government we outlaw the collection of intelligence in the RF spectrum to prevent the inadvertent exposure of a US citizen to spies in our government who do this for a living. I appreciate the concern. However, to outlaw all RF collections means those collections are not available to the military. Radars are the number one threat to our military personnel who fly. In order to survive in a hostile environment fraught with radars looking for them, it would be advantageous for those same personnel to be able to see the RF that is actually looking for them. Sadly, due to these laws, we actually tie our hands behind our back. As disadvantaged as I argue that radars are, we disadvantage ourselves even more by restricting the RF sharing that could be done to identify them. That is almost unconscionable when you think about it. To deny our military the maps of the RF that they fly through is like telling the Army we are not going to give you maps of the terrain today. I think about it a lot. An enemy radar using RF to look for our aircraft in a foreign land is the farthest thing away from collecting information on me from my cell phone call. The two of them are not the same. Something has to change. Leadership in our country has to understand the difference between a radar producing a pulse of RF energy to bounce off the skin of an aircraft and a wireless phone call. Currently, they do not.
With all these disadvantages, why do we even use radar? As Alexander the Great said, “If you defend everywhere, you defend nowhere”. When you have oceans of sky to defend, even that one little blip, provides a cue of early warning. You can’t do anything about it…but at least you know it’s time to get ready. Like a tripwire in the woods. And initial indication that something is coming for you. The wolves may not be at the door, in the case of the three little pigs, but the wolf is definitely inside the perimeter. This important detail can be ascertained by a single blip on a radar screen, amongst the additional confounding knowledge that this very sparse blip of information, could actually be wrong. It might be a false alarm. An entire field of statistical mathematics was created just to deal with this knowledge that the blip could be false, but considered real. OR the blip could be real, but considered false. OR the blip could be real, and considered real. OR false, and considered false…those last two are the good outcomes but nevertheless we still have uncertainty about their correctness. This just sucks. The way we look at these numbers is in the form of what is called a Receiver Operating Curve, or ROC. It’s basically a measure of how shitty your receiver could conceivably be. Unfortunately they took on a life of their own and have extended into all areas where someone might consider using a receiver, such as in the case of imagery for medical purposes. Now instead of explaining to a patient that there is a blip in their brain, the doctor must explain all of that shit above…thus putting the interpretation of all that nonsense, on the patient. When considering something like brain surgery, it would be better to have more sensical information. What we can do with radar that we can’t do in the medical industry as well, is sample each environment to get a feel for the noise that’s out there. If we sample the environment until we get a constant number of blips from the background noise, we have tuned the equipment correctly to the environment. Then we just need to wait for a blip that rises above this constant false alarm rate (CFAR) to declare the blip as something worth looking at…all other issues still apply. It’s ironic that our electronics were so bad, so many false alarms, that the engineers came up with a way to use them.
In the never ending quest for more information, the way it was decided to do this, was to add another radar to the mix. One more radar, one more blip. And another, and another. String enough radars together and you create a network of systems providing one blip of information each. We call this an integrated air defense system, or IADS. The United States built our first one in the 1950’s and 60’s. It was called SAGE and it ushered in the age of computers to deal with all the math. Principally its purpose during the cold war was to detect the Soviet Union should they decide to conduct a sneak attack from the air. So based on that paranoia, we put radars everywhere. We no longer do that…and behold, China flies over the United States with a balloon and the Country shits its collective pants. That’s because China didn’t announce their presence with ADS-B as they flew over. We shot that Chinese intruder down from a fighter jet with an expensive missile. I’ve addressed the folly in that endeavor in another paper. (I actually published a shorter response in Air Force magazine to admonish the Country’s leadership for doing such a bone headed thing -- I did not get a call from the President).
So currently, we do not defend the United States with an array of radars of any sort. We defend a single city with an IADS. We defend Washington DC. And to be clear, we only defend a handful of point targets, not the city at large, or the surrounding metropolis of Americans. So when you hear the criticism of our Air Defense not seeing the Chinese High Altitude Balloons, because our radars are not tuned to see those high altitudes and those slow moving, mostly porous fabric filled air bags, because we are looking for aircraft. Fear not, we are not looking for aircraft either. Those radars don’t exist. That is not to say we need them. We did shut them down for a reason…in favor of the much more reliable and data filled system that is ADS-B. And when I say more data and more reliability we are talking about orders of magnitude. It’s not even close. And, then there’s the cost. You need an internet connection…yes all aircraft have to have a transponder…but those are dirt cheap as well, easily under $1000 bucks. Radars throughout the Country would cost billions…probably trillions of dollars.
What then, people, are we to do?
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