Stuart wrote:Let me give you an example of how to generate a pencil beam that has very limited spread and is only a few millimeters across using WW2 technology.
Stuart, many thanks for posting this. I hadn't wanted to argue over classified systems when I'm not privy to such data and you couldn't discuss them regardless; this example however greatly clarifies the fact that, as I'd suspected, we were indeed talking past each other. We are in complete agreement that it's quite possible (and indeed, has been practical for decades) to track and image objects, and to provide guidance, etc, via radar systems with a very high spatial precision.
The sole point of contention in this mini-debate is whether or not all the power of a microwave transmitter can be focused into a very narrow angle - to summarize:
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Stuart says: The SPY-1 can generate a "pencil beam", putting almost all the power of the whole array into a spot just a few centimeters across on a target many kilometers away.
muon (and BR7) says: No, that violates the laws of EM propagation.
Stuart says: Yes it can, many modern classified systems do indeed have these capabilites, and while I can't say more about those, even very old radar systems could perform such feats that show this is possible.
muon (and BR7) says: Of course all these things are possible, because they don't in fact require the transmitter power to be focused in the way you were originally claiming, i.e. no violations of the laws of physics are required to accomplish any of that.
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In short, as you put it, it simply isn't relevant whether or not one can so tightly focus EM power transmission, for none of these radar-system capabilities depend on such a feat. EXCEPT, of course, the original point of contention itself: while you can do everything else described with a radar, you can't cook something at such a long range with an array of that diameter at that frequency, because the power focusing limit IS relevant, and crucial, to that specific point.
Stuart wrote:We take a standard dish antenna and mount it slightly assymetically so that the center of rotation of the disk is slightly off the axis... [SNIP]
To simulate this, get a sheet of paper and roll it into a cone (the proportions of the cone don't matter but start with a long, thin one and experiment). That simulates the radar beam generated by the set. Now, get a knitting needle and tape it to the inside surface of the cone so that its aligned with the axis of the cone. Now, hold the knitting needle by the end at the small end of the paper cone and rotate said needle. You'll see the beam sweep around the axis represented by the needle. You've just generated a literally needle thin pencil beam that's independent of the size and shape of the paper cone.
This nicely validates what I was originally trying to say. To wit, you can in fact have a rather wide beam (indeed - note the bolded parts - as you yourself note, it doesn't even matter what the proportions of the cone are, i.e. how wide the actual transmitted beam happens to be!), and this technique will still work fine. (As an aside, the picture isn't that simple, as the beam will not have razor-sharp edges, but the example you give still stands as a very good illustration of the fact that you do NOT need to tightly focus the beam itself to perform highly accurate guidance or tracking.)
Even more importantly, this clearly illustrates our apparent mis-communication here. You refer to the virtual line in space designated by the outer edge of this moving beam as a "pencil beam", but there's no physical reality to this line. There isn't actually an extremely narrow and intense beam of microwaves, along which the missile rides. And that's what I was referring to as a "pencil beam", an extremely narrow subtended angle within which most of the power of the entire transmitter would be focused. Again, you don't need to focus the transmitter's power so tightly to accomplish such guidance and tracking... but you WOULD need to do this, if you were going to cook something at range.
Simon_Jester wrote:on a side note, conical sweeping gives you a needle beam, but it doesn't get you past the diffraction limit. The needle has orders of magnitude more energy flowing down it than the area swept by the main beam, but on a millisecond-by-millisecond basis it isn't getting hit with more energy than the radar could otherwise achieve at a given range. So you get your target illumination all right, but if you can't achieve cooking at long range just by pointing the beam at a wall and letting it sit there, you won't be able to achieve it this way either.
And you're certainly not putting the full power of the array into the needle beam.
Indeed.
An even simpler example may serve to better illustrate this fundamental issue. Per the link BR7 posted, please see this image (it's bigger than SDN likes to see inlined, and I didn't have time to look over that site's usage rights re editing and re-posting, so I linked):
Diffraction Spot
That's a plot of the EM wave amplitude (E-field strength, square root of power), of a beam striking an x-y plane. Note the shape of the central peak; it's not a point, nor is it a flat-topped cylinder (i.e. the intensity of the illuminated disk varies with the radius from origin). And we can take advantage of this fact to accomplish all sorts of useful things with a radar system. Visualize the radar beam sweeping across a target: the target won't simply be "in" or "out" of the beam; rather, as the illuminated spot sweeps across the target, the target (indeed, individual parts of the target) will be subjected to a gradually increasing and then gradually decreasing intensity. And this can be utilized to more accurately track or image or guide objects, within the beam (e.g. sub-beamwidth resolution). Again, no argument here that one can accomplish all these things, quite easily in principle, with a radar.
HOWEVER - and this is common to all focused EM beams: while one can vary the shape of the irradiated spot (with various transmitter configurations), and while one can also vary the size of the spot, there is a fundamental limit dictated by the laws of physics that says one can NOT make that spot smaller than a certain size, for a given frequency and transmitter aperture and target range.
Of course, there are many much more sophisticated methods of beam control and tracking than the simple mechanical one you mentioned; one can electronically chirp the beam, wobble the beam, pulse the beam, among countless other (actually fairly well-known in the communications industry) beam-shaping techniques; and yes, active phased arrays permit one to use multiple interfering beams, multiple simultaneous frequencies, etc. Yet none of this permits one to focus the power of a beam more tightly than the diffraction limit, which is what is required for an effective directed-energy weapon at microwave frequencies.
Note also, thanks to Lorentz reciprocity, if a given physical antenna could transmit a particularly narrow beam, that same antenna could also receive signals with that same angular resolution. Which would mean that radio telescopes wouldn't in fact need to be much larger than optical telescopes to achieve similar resolution. Or, indeed, that any sort of telescope (these same principles apply to all EM frequencies) wouldn't need to be particularly large to have an arbitarily high resolution! I grant there are a lot of good people continually working on classified improvements to military systems, but there are also a great many good people working on related improvements to commercial and scientific equipment (from Bell Labs and AT&T Long Lines towers back when, to modern astronomy across the entire EM spectrum), and I find it extremely difficult to believe that such an incredibly revolutionary breakthrough would not have been independently rediscovered (a literal revolution, as much of what we thought we knew about EM, up through QED, would need to be drastically revised if this type of extreme power focusing were actually possible - if only I could have told Feynman how wrong he was back at Caltech before he died, LOL!). There is in fact an interesting thread about all this in the SLAM Library -
see here - where Mike and Starglider (et al) noted that the physical size of EM sensors will place an absolute limit on the maximum achievable physical resolution (pre-image-processing). With a receiving system (a sensor), there are ways around that, e.g. using an interferometer composed of multiple smaller widely-spaced linked receivers; however that doesn't work for power transmission - as I'd mentioned previously, the "thinned array curse" means that if you try to use a transmitter with such gaps, most of the power will be wasted in sidelobes. The only way to tightly focus a beam is to use a physically contiguous transmitter (dish, array, etc); and if you want a more tightly focused beam, you have to either use a larger transmitter, or a higher frequency.
Stuart wrote:If you're really fascinated by this kind of thing, the best way to get involved is to get hired by the companies that design the equipment. Essentially that's Lockheed-Martin, Raytheon, BAE Systems and Thales...
I know. For what it's worth, my job involves configuring and deploying microwave and millimeter-wave communication links, and I've dealt with OEM suppliers and engineering teams from major military component suppliers like Endwave. Again, I've never had access to classified data, but I find it hard to believe that a concept which could instantly generate so many billions of dollars in increased telecommunication system efficiency and performance (every broadcast engineer in the world would be drooling over the prospect of such boosted link budgets!), would not have been rediscovered in the commercial market.
Stuart wrote:That's why, for sheer shits and giggles, engineering beats pure science any day. Anybody can create a new scientific law but an impressive shiny toy (especially if it costs a billion dollars or so) is really something.
Couldn't agree more - I almost went into particle physics, but couldn't stomach the notion of spending my whole career searching for a single elusive particle that might not even exist at all! That said, I don't believe that engineering of whatever sophistication could actually break physical law... we can do amazing things in the year 2009, and it still looks as though we're going headlong toward the Singularity; but at least until we reach that point, there are still fundamental limits that constrain all engineering, and breaking through those limits would mean a profound revision to our understanding of the universe. Obviously, this story is full of such revisions, with portals and other dimensions with their own subset of physical laws, but presenting an existing military system itself as being such a paradigm shift just strains credulity too much, at least for me.
Stuart wrote:Very briefly, the reason why the capability discussed isn't militarily viable is that it doesn't work too well against aircraft. It warms them up by a few degrees but that's all...
I would agree completely. And the reason for that limitation, I would submit, is that you simply can't focus these frequencies that tightly with a reasonably-sized transmitter.
Stuart wrote:As to using the same technology as a dedicated weapon, a lot of research has been put into that area and its still going on. We haven't got a viable weapon yet and given some other factors, the prospects don't look good. To some extent, the same technology has been leveraged into non-lethal weapons; for example crowd dispersal by making people feel uncomfortably hot. That has its problems as well. In that application, its a great help that human flesh is much less temperature-tolerent than metal. But, as a directed energy weapon, lasers have more potential than microwave frequency weapons. As far as I know. It's quite possible somebody is reading this and grinning broadly because he works on something that says otherwise.
Yes, I mentioned the
Active Denial System previously - it's actually a millimeter-wave system (W-band), so in theory it could be focused much more tightly than lower-frequency microwaves (of course, you wouldn't want such tight focus in a non-lethal weapon!). However, millimeter waves are much more prone to atmospheric attenuation than lower frequency bands; near the 60 Ghz oxygen resonance attenuation can reach some 15 dB/km (a severe range limitation), and all higher frequencies are susceptible to rain fade (a ground-based system that would be rendered ineffective by foul weather would presumably be militarily unacceptable).
Indeed, lasers (IR to optical band) are the main practical way to make such an EM DEW (as millimeter-wave and terahertz frequencies are so severely attenuated by humidity and/or atmospheric gases). Again, I submit that the primary reason for this isn't some intrinsic superiority of lasers over masers in damaging a target (although there are substantial differences in reflectance, possible shielding, material effects, etc), but the simple fact that microwaves just can't be focused tightly enough - with any physically-possible technique - to be effective.
There are many ways HPMW weapons could cause damage though, particularly to electronic systems as you'd mentioned in-story; and via pulse-shaping additional transients could deliberately be induced, etc (as HERF and TEMPEST topics are also deeply classified, there's no sense going into that here; same with more speculative psychotronic effects on living targets). But all of that is irrelevant to this one point: when we're talking about simply heating a target, via pure brute power, focusing and power density concerns do set these fundamental limits.
Anyway, enough rambling on my part, and with Chapter 26 now up, I'll refrain from posting more about this here, unless there's lots of ongoing interest. Also, I do note that you actually never made any of these ultra-tight focusing claims in-story, as it was only in the story discussion thread where you said this:
Stuart wrote:What is that maximum power? Classified but we can take it for granted it's far higher than 4,000kW and for an AEGIS-ABM its higher still... [SNIP]... Now, note, target designation beam. They're called pencil beams for as reason, that's roughly how big they are. At 70 - 80 miles, that beam is tiny. How small? Classified. But, using other fire control radars as an example, we're talking a beam that's probably a couple of centimeters across at most. Let's be really generous and assume its 5 cm across, that means its area is roughly 75 sq cm and its getting a power input of way over 4,000 kW. I'll leave somebody else to do the maths.
So, the story actually stands essentially as-is; and this is merely an in-thread digression.
A microwave beam of that intensity would be as destructive as any megawatt-class laser weapon system, such as those now in development. A 40MW beam with a dwell time of just 1 second would deposit energy roughly equal to 10kg of HE directly into an absorptive target! Development of mw-reflective shields for aircraft could offer some protection, but then the aircraft would be brightly visible on radar, defeating all the RAM and RAS incorporated into modern airframes. (The very fact that you point out that such microwave transmitter arrays need powerful active cooling; then by focusing that power into a spot thousands of times smaller in area, indicates the sort of temperatures that would be achieved at such a focus, if it were possible.) But, ultimately, the notion of focusing microwaves so tightly would indeed violate the laws of physics. Lasers could do this, masers of reasonable size could not.
BR7 wrote:Except that no amount of engineering can surpass fundamental limits. If it does, it means that the understanding of the physics was wrong. In this case, I haven't seen enough evidence to convince me that electromagnetic propagation laws as currently understood are wrong. That's the difference between an engineering problem and a physics problem. It's impressive if you build the first supersonic vehicle, but if you want to build the first superluminal vehicle, you'll have to rewrite the laws of physics first.
[SNIP]
As nickolay1 said, it's a phased array. Tracking abilities are the kind of detail I would expect to be impressive, but secret, as Stuart has alluded to. Tracking that well causes no physics problems I'm aware of.
That is the best summary of all. A couple analogies to what this issue really represents:
ANALOGY 1 (energy and weapons performance) : Suppose you wrote in an upcoming chapter about a nuclear device, about to be used in the war. This device is reportedly a new innovative design (that needs to be used for some in-story reason), described as a pure-fusion weapon, with a certain expected yield and a certain mass. Now, some readers might object to that, claiming there's no possible way such a device could be constructed with anything like our current technology; and you might respond, given your classified knowledge, "erm... I can't tell you any more about that".
Yet there's no fundamental problem here, as it's simply an ENGINEERING challenge; with a sufficiently ingenious design, it might well be possible, and certainly it doesn't violate any fundamental physical laws. However, if the figures you'd presented indicated the device converted 2% of its entire mass into energy, or 150% of its entire mass into energy, that would be an infinitely more profound issue (at a 2% conversion, it would have to be some type of total-conversion device, thus requiring at a minimum dramatic revision of the Standard Model; and at a 150% conversion, much of what we thought we knew about physics would have to be tossed out the window). It's a fundamental physics question, not a matter of clever engineering. And suggesting that microwaves could be brought to a point focus at such ranges is that sort of problem - it would trash current physics (EM no less, that we thought we had completely understood since QED was developed!).
ANALOGY 2 (communications) : Suppose you wrote in an upcoming chapter that a military unit had sent an encrypted message via the strongest available cipher, which is stated as being Rijndael. And that message had been intercepted and decrypted by the enemy (one of Heaven's beings, perhaps). Some readers might object, pointing out that AES-256 could not be brute-forced, even with quantum computers. And you might respond, "erm... I can't say any more". (Although, I guess if you had knowledge that NSA had broken AES and made such a hint, we wouldn't hear from you again for quite a long time...) Anyway though, again, there would be no fundamental problem here, as this is also an "engineering" problem, in that a new mathematical technique might well break the cipher. However, if you wrote that the message in question had been transmitted over a conventional telco copper 24ga twisted-pair landline, at an effective speed of several Gbps, then this would be an infinitely more profound problem, as it would violate the fundamental laws of physics, the Shannon limit. Again, the notion that microwaves, through sufficiently clever engineering, could be so focused, is that sort of problem.
In the end, no, I don't say "it's impossible", for someday there may well be such a revolution in physics - but nonetheless, being able to accomplish such a feat of EM focusing would, in and of itself, require this sort of profoundly deep paradigm shift in science.
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Simon_Jester wrote:On a semi-intuitive level, I think I can see how an AESA might be able to generate that kind of beam... I think. Don't take my word for it, because I'm not in a good position to put in the time to do the math right now.
I'd like to hear about it, half-baked or otherwise!
" - 
Over the years, I have thus far avoided reading this site while at work, and all that will probably change now...
