China's High Frequency (HF) or Over-The-Horizon (OTH) radars

[gambit]

Gambit, I told you this before and I'm getting tired of repeating myself.

Stop quoting a citation from 1997, which was 17 years ago. Signal processing has advanced tremendously during the last two decades. "Look down shoot down" radar has been able to exclude terrain clutter.

How hard is it to write a software filter to exclude the false echo and virtual image? You are like a simpleton.

Try paying attention to your own stupid outdated citation.

If you want to see a real simpleton, go look in the mirror.

If the passage of time means a problem must have been solved, may be China have a warp engine somewhere ?

Clue for you, simpleton...

Prior to the F-117, Ufimtsev published his math in the Soviet Union. Were there any need by any enterprising person, in and outside of the Soviet Union, to have a low radar observable body solely for the purpose of radar avoidance ?

Same for the development of a radar system to detect objects beyond the horizon, who had the need for such ? The reason we want to detect something via radar is to effect some forms of control and authority over it. So the radar is a boon for commercial aviation and for the military. But outside of the military, who in the commercial sector have a dire need to detect and exercise authority over targets ?

High-Frequency, sky-wave, Over the Horizon Radar (OTHR) Technology - Federal Business Opportunities: Opportunities

We solicit the interest of vendors, organizations and/or consortia with OTHR expertise in one or more of the following areas:

1. System architectures
2. Hardware components
3. Software development and maturity
4. Radar Propagation and Performance modeling
5. HF antenna array design
6. Test methods
7. Signal processing methods
8. Target localization and accuracy improvement including altitude estimation methods

In 2008, the USAF solicit technical information about improving the current OTH radar technology. Note the highlighted item 8.

The US already operated OTH radar systems during the Cold War when China was still begging the Soviets for tech scrap. The Cold War ended in 1991. Up to that time, the best military thing that made China famous was the venerable AK-47. Now according to you, China gained leaps and bounds in radar technology and solved problems that plagued the US and the Soviet Union for decades.

IEEE Xplore Abstract










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Over-the-horizon radar continuous-wave interference suppression using harmonic least-squares fitting

High Frequency (HF) skywave over-the-horizon (OTH) radar is routinely affected by radio frequency interference (RFI) from natural sources (e.g. lightning), and transmissions from other users, such as continuous-wave (CW) signals. Although adaptive processing effectively mitigates interference and noise, it can impact negatively upon target detection in some cases. This paper describes a simple filtering technique, harmonic least-squares fitting (HLSF), which has potential for application throughout the OTH radar signal processing chain. In this paper we illustrate HLSF application for clutter suppression, transient detection, and CW interference suppression. In each instance HLSF application demonstrates advantages over commonly used techniques.

According to you, it must be very simple to write filtering algorithms to exclude clutter and multi-path anomalies. The above IEEE Xplore paper was submitted in a conference in Sept 2013.

If it was that easy to write filtering algorithms, then what was the point is submitting a paper that propose using least squares algorithms ? Note the highlighted. What are those other 'commonly used techniques' ? If a radar engineer show me this least squares algorithm, I probably would see it a mathematical version of cornbread, and I actually worked with radars, whereas you can barely tell the difference between a screwdriver and a hammer.

The only major customer for an OTH radar system is the military. The system require large areas of land, not just for the arrays themselves, but also for security purposes. The area should be away from high population centers, not just for technical reasons such as interference, but also for security purposes. At the same time, the area should be reasonably accessible in order to conduct daily operations and maintenance. That means unless there is a wide scale commercial need for OTH radar systems, any development and the inevitable need for wide scale testing will stagnate.

But this is not the issue, which is your absurd claim that it is 'almost impossible' to deceive an OTH system in spite of the real physics facts that nature is already doing it. Currently, any OTH system is good for 'cooperative' targets, meaning targets that allows themselves to be found. That allowance could be deliberate or ignorance but most targets are usually ignorant that they are being scanned by an OTH system. Only those who do not want to be found takes efforts to make themselves 'non-cooperative' targets, such as smugglers who flies at low altitudes or the military.

So if nature is already making problems for an OTH system even when the targets are cooperative, what make you think that it is 'almost impossible' to deceive an OTH system when there are 'non-cooperative' targets ?

Never mind answering that rhetorical question. We already know the answer: 'Chinese physics'.

Look at your diagram. Are you telling me that this is a serious problem? The missile knows its own GPS coordinates. The enemy aircraft is either at a positive altitude or somewhere below ground. Are you claiming the software is unable to exclude the negative altitude solution? Get real.

Where altitude = zero, ignore the signal. Duh!

Put in an allowable range where target may deviate from prior signal return by five degrees. This should allow a correct and continuous track to the target.

Talk about being dense -- YOU.

What I posted was to illustrate what multi-paths propagation look like, if we are to visualize it. It was not about the missile, you dope.

 

[Aegis DDG]

@gambit Can you tell how the radar detracts from the Ionshpere/atmosphere and how it get it's target from other ships in the sea? E.G. The USN is monitoring an Russian transporting military cargo vessel near it's shorelines and uses OTH radar, how will the computer designate the intentional target if the USN? Will computer algorithm do the work? What the software maturity in USN OTH and other radars compare PLAN radars based on your current knowledge? I first heard about OTH radar when I watched an video of how the DF-21D will use this radar to an homing instrument to attack USN carrier groups in it's AAD/AAA doctrine.

 

[shuttler]

@gambit - YOU

why is " harmonic least-squares fitting " applied here?
How does it work out?

IEEE Xplore Abstract
Over-the-horizon radar continuous-wave interference suppression using harmonic least-squares fitting

 

[Martian2]

Military Implications of China's Over-the-Horizon Radar Network

China's Over-the-Horizon (OTH) radar program started in 1967. As of the 1980s, we know two more OTH radars were built. China's OTH-Backscatter (OTH-B) radars are bistatic systems, where the receiver is optimally positioned to maximize the radar reflection from the area of surveillance.[1]

In the past, the limiting factor had been a lack of computer processing power. As an analogy, it's hard to create an useful MRI image with limited computing power. Obviously, China no longer lacks computing power and builds the world's fastest supercomputer at 33.86 petaflops.

Since China has multiple OTH-B radar transmitters and receivers, the whole system can be tied together into a giant interferometer. There are multiple emitters and the reflected signals are being recorded by multiple receivers. It is virtually impossible to stay hidden from China's Over-the-Horizon Radar Network.

Let's take a look at the military implications.

1. A B-2 bomber should be easily detectable. The Chinese OTH radar signal is bounced off the ionosphere and illuminates the B-2 from above. Using the AREA RULE, the B-2 has a wing area of 5,140 ft² (478 m²) that will reflect the Chinese high-frequency (HF) radar waves.

2. The B-2 is a large aircraft with dimensions of 69 ft (21.0 m) length, 172 ft (52.4 m) wingspan, and 17 ft (5.18 m) height. Also, B-2 control surfaces like the elevons and split rudders are on the scale of meters. All of the dimensions of the B-2 and its control surfaces fall perfectly into the range of HF radars at 3-30 MHz (or wavelengths between 10 and 100 meters). This means the physics phenomenon of half-wavelength resonance will ring the B-2 like a bell.

3. The Chinese OTH Radar Network can also easily see the refueling aircraft for a B-2 flying from the United States. China can choose to intercept the tanker or the B-2 while they are coupled during refueling. Both aircraft are extremely vulnerable while the KC-135 takes 30 minutes to fully refuel the B-2 or 25 minutes for the KC-10.[2]

4. China's three stealth fighters provide excellent test subjects for the OTH Radar Network. The Chengdu J-10, Shenyang J-31, and AVIC Lijian stealth UAV have small wing areas. The Chinese OTH Radar Network can be tuned (via software algorithms) until it can find the smaller Chinese stealth fighters.

5. China can conduct actual field tests against the F-22 and B-2. There were F-22s flying around Japan and a squadron that will be based at Kadena.[3] There are B-2s at Guam, which is near the outer range of the Chinese OTH Radar Network.[4] Also, B-2s have occasionally been sent to South Korea to help fine-tune the Chinese OTH Radar Network.[5]

The bottom line is that China can see U.S. "stealth" aircraft. That's a good reason not to build any more expensive F-22s and B-2s. They are not stealthy against the only country that matters.

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1. PLA Air Defence Radars | Air Power Australia

"OTH-B Over-The-Horizon Backscatter Radar

China is reported to have developed its first OTH-B radar back in 1967, although its designation is not known. Since the 1980s two further installations have possibly been added to the inventory, with at least one system looking out into the China Sea area reportedly to target (US Navy) aircraft carriers.

Backscatter systems function at the upper end of the High Frequency (HF) band, typically between 12 and 28 MHz.

OTH-B radars are bistatic systems, this is where the transmitter and receiver use different antennas at widely separated locations to achieve detection results. The importance of these systems is that they are not limited by line of sight, as are most radars, but they do require a very significant amount of processing power. This was the limiting factor with early Chinese OTH systems, but may no longer be the case.

Because of the very long wavelengths involved, to be efficient, the antenna arrays are extremely large as indicated in the picture above.

China's OTH-B is said to use Frequency Modulated Continuous Wave (FMCW) transmissions to enable Doppler measurements, the suppression of static objects and the display of moving targets.

On 14th November 2001 china.com reported that CEIEC was (then) developing a new OTH radar because only one system was currently available (presumably the one shown at its web site), which is the one assumed to be sited near the HQ of the South China Fleet at Guangzhou."

2. David S.

3. F-22 Raptors deploy to Kadena Air Base, Japan | Pacific Air Forces

U.S. to deploy 12 F-22 Raptor stealth fighter jets to Japan | The Aviationist

4. B-2 Stealth Bomber Crashes in Guam; Pilots Eject Safely | Fox News

5. U.S. says it sent B-2 stealth bombers over South Korea - CNN.com