As for knowing when and where the planes were flying, true, true. But then again, they deployed one van to try to detect the planes, in the one farm, and if the objective was to suggest that the passive technology could end up being useful in a military situation, that might be enough.
The argument is that the F-35 is invisible. If passive detection seems to have any effectiveness, even slight, in detecting F-35s, that ought to guide investment into passive detection and into upgrading the F-35’s stealth to avoid passive detection.
INAE, but it feels like there is enough here to cast the claims of complete invulnerability to detection in doubt.
I would really love to see the actual Probability of Kill numbers for the US missile fleet. I know that's never going to happen/they're going to remain classified for a _long_ time, but the kid in me really wants to know "does it actually work?"
Air-combat is "hard" to answer the "does it actually work" because it is very much like high stakes chess in the air. A lot of times you fire 1 missile to make the bogey defensive, and multiple missiles to kill. This gets even more complicated when you factor in differences in pilot skill, numbers, chaff, and electronic counter measures.
Edit: fixed seeker range
You obviously need strong signals for passive radar to work but those could be positioned inland and they don't need to be where the passive radar is, making it harder to disable it.
Yes, they each span a wide range of frequencies, but every frequency range spans a wide range of frequencies. These two are as close as you can be.
https://en.wikipedia.org/wiki/Microwave
https://en.wikipedia.org/wiki/Very_high_frequency
Not coincidently, VHF Radar is defined to be between 50 and 330Mhz, which actually overlaps both Microwave and VHF television.
Now as to the main question, if I set up a device to interact with radar at some frequency and attach it to a stealth airplane, what frequencies would you expect it to effectively interact with it (assuming it's tuned at all, they could just be attaching a big piece of flat aluminum)?
Answer: If my device has peak interaction at frequency F, you will see harmonics, so you will see significant interactions at 1/8 F, 1/4 F, 1/2 F, F, 2 F, 4F, 8F.
Airport radar is around 3Ghz. So if the radar reflector operates at around 3Ghz, it will also work pretty well at 1.5Ghz, 750Mhz, 375Mhz, and even 187.5 Mhz. 187.5Mhz is TV channel 6 or 7, depending on country. Half again is 93.7 is FM (which the article specifically mentions).
I mean the goal of a radar reflector is to send radar signals back to their source, they are super effective. They don't really work like antennas generally, but the pictures of the F-35's reflectors do not look typical, or like a boat's radar reflector, and I have no idea what principle they use.
A tiny radar reflector has the cross section of a huge object, because it intentionally has right angles that send signals back to their source without scattering them in other directions (as much as is possible).
Passive radar still requires the object to reflect signals, it just doesn't require the signals to be reflected back to the source of the signal. Consider a monitor with an anti-reflective coating (so lets take a non glossy monitor). It is effective at reducing the reflection of the window behind you, it uses a thin film to cause destructive interference so that the light coming in the window not reflected, and you see a greenish-purplish image of the window instead of getting a bright reflection. However, if you take a flashhlight and shine it down on the monitor from near the top of the monitor, you will easily see the glare from the flashlight as it illuminates the monitor.
I think this is a good analogy for active vs passive radar. The F-117 was built to avoid right angles, this is like the light from the window behind you. The F-117 won't send radar back in the same direction it came from, so active radars are thwarted. However, if it is being 'lit up' from somewhere else, it is not as effective since by not sending radar back to where it came from it sends it in other directions instead.
However, it also has a coating to just straight up absorb radar. The F-35 is much more reliant on such coatings, and so it should scatter very little EM radiation in those frequencies, regardless of whether the detector is in the same location as the transmitter.
You will not see harmonics at fractional (1/2 F, etc...) frequencies of the fundamental, though you will likely still see some backscatter.
Retroreflectors[0], to include the Luneburg lenses[1] mentioned in the article, function by directing radar energy parallel to its incidence direction. These reflectors will not significantly increase the plane's RCS for passive/bistatic receivers. Even if these reflectors did increase RCS omni-directionally, it is unlikely that a reflector designed to operate at 3 Ghz (10 cm) would also be designed to operate at 187.5 MHz (1.6 meters).
[0]https://en.wikipedia.org/wiki/Retroreflector [1]https://en.wikipedia.org/wiki/Luneburg_lens#Radar_reflector
Sensitive VHF radio receivers, tuned to transmitters that are located beyond line of site, can very easily detect VHF communications reflected off of a very small airborne target.
I can sit in my office with a spectrum analyzer and watch the signal strength of a distant digital TV broadcast station come in and out of view when an aircraft flies overhead.
Couple that technique with a DF network and far more sensitive receivers and GPS timing, and building a passive radar to defeat stealth technology become far easier than you think.
More interesting would be whether those planes actually had the full stealth coating and various other "stealth settings".
It's hard to get your head around a plane the can climb over 1000 feet per second (F22: 62,000ft in 60 seconds).
The important question is whether or not they can pick it up when it doesn't have markers fitted as they claim they can. To quote Carl Sagan, 'extraordinary claims require extraordinary evidence'. If (and it's a huge if) they can do what they say they can then stealth might be rendered pointless, and that changes a lot.