Chinese Radar Developments - KLJ series and others


Tam

Colonel
Registered Member
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It sounds like marketing talk. Every company talks like they are a pioneer of something. Like Apple talking about their innovation while copying Samsung.

300 million investment doesn't sound something that China, Russia or even Spain can't afford into the technology.
They have to do it because no one else in the US does. To have a custom fab just for your own purpose of making it "China-free" is very expensive, since you cannot amortize the fab doing civilian and commercial applications. This has some precedents for example, in a case involving a certain chemical that is used to make the propellant for the Hellfire missile. Turns out no one in the world makes it but this obscure plant in China, and they have been importing this chemical for a while already, only to discover under audit the chemical was coming from China. So the Army had to finance to make a plant just for the exclusive purpose of making this chemical in the US.

Going back to Gallium, China is the leading producer of both crude and highly refined Gallium. Russia is also high in the list.

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While the US and other Western nations wants to corner GaAs and GaN for military applications, China wants to do it for commercial and civilian reasons, and by doing so, made the product cheap.

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Commercial applications range from telecom base stations, to smartphones, TVs, and not the least, LED diodes. The Chinese government was pushing for LED lighting production to replace all forms of other lighting in a vast countrywide program to save energy. That's why you see GaN even on those LED flashlights you can buy.

The Chinese luxurious exuberance of throwing AESA solutions into just about everything --- 5G will use it (back to Huawei and ZTE again) --- has something to do that for China, doing it this way is not expensive for them, they are brimming with the sources for it, and yet it would be extravagantly expensive for the US. Cost was the reason why the SPY-4 AESA S-band search radar was removed from the Zumwalt class.

So, any advantage gained from GaN disappeared in the past years, or will disappear before 20s.

After all that left is the size / cooling capacity differences, and the experience with the software .

In the latest the Russians had a clear advantage, in the later the USA has a clear disadvantage compared to Ru/Cn
I believe Raytheon's first GaN based radar is the MPQ-65 which is the new radar for the Patriot system. Japan however beat them to the punch in naval radars, with the first GaN radar on the Asahi class destroyer, which is a new variant of the Akizuki class. This is a virtual tie with Germany, whose Cassidian is making the TRS-4D which is the radar for those expensive F125 frigates. However it is also said that the radars for the Type 055 are also using GaN which will put the ship in the bleeding edge of technology but China keeps all information to itself to keep you guessing. Raytheon wants to put GaN radars on the Flight III Burke as the SPY-6, currently in testing, and a smaller version of it is the EADS, meant for the FFG(X). Thales Nederland is offering APAR Block II which is GaN based.

I am interested to know if the new AESA radar proposed for the JF-17 might be GaN based. As these substrates run cooler than GaAs, it would make it possible for the radar to be air cooled and use less power. Conversely, if you allow it to be liquid cooled and is willing to throw much more power at it, it will have greater performance.
 

Anlsvrthng

Senior Member
Registered Member
Not talking about slit diffraction, which you can also call frequency steering --- change of frequency of a radio wave going through a slot changes its direction.

I am talking about the signal loss between the main amp and the emitting array. Signal loss and distortion between main amp and emitters by signal travelling through line path is significant enough, that its one of the reasons justifying AESA development.

Going back to frequency steering or "squint" in short, what changes the frequency is the delay of the signal between the amp to the emitter. This is why the lines from the main amp to the emitters must be of the same length.

As I remember from the Raytheon presentation the signal loss due on PESA is 3 db ( half of the energy).

It seems as a lot at first, but the 60 degree off axis beam steering has similar energy loss ( actually the energy will be in a wider main lobe) and the loss of aperture size on the receiving gives similar loss.

So, a gimbaled PESA radar can outperform a non gimbaled AESA radar in off axis directions, even if the AESA has twice as much power .

At the end of the day the most important it is the training / capability of the organisation, radar operators, pilots,officers, position of the aircrafts / radars /TELs and not the technical specs of the equipment.
 

Tam

Colonel
Registered Member
As I remember from the Raytheon presentation the signal loss due on PESA is 3 db ( half of the energy).

It seems as a lot at first, but the 60 degree off axis beam steering has similar energy loss ( actually the energy will be in a wider main lobe) and the loss of aperture size on the receiving gives similar loss.

So, a gimbaled PESA radar can outperform a non gimbaled AESA radar in off axis directions, even if the AESA has twice as much power .

At the end of the day the most important it is the training / capability of the organisation, radar operators, pilots,officers, position of the aircrafts / radars /TELs and not the technical specs of the equipment.
I think you might have misread me but Brumby got it right. PESA has both significant insertion and receive loss.

Gimballed PESA helps but you can also gimball an AESA. Soft factors like training happens to both, so even the users behind the gimballed PESA can also be in the less trained side of things.

You can reduce PESA receive loss through a distributed receiver system, for PESA, it should be done on the subarray level, a single A/D converter serving a minor set of receiver elements.

In the end though, there is no point in having a PESA, your cost is not going to be any better than AESA as the cost of AESA modules come down with mass production of the AESA modules. The quality requirements for building parallel line feed PESA is very high, since every line feed from the main aimp transmitter to each emitter has to be of equal length and resistance, and a QC variance that causes a time delay on the line, which can cause a frequency change on the emitter and therefore you get squint, with this particular emitter not working in unison with other emitters, causing sidelobes and scatter. The signals in the lines themselves can result in distortion also because of various induction forces inside the radar from other electrical and magnetic sources. And of course, the resistance within the line feed themselves result in some loss.

AESA simply eliminates this complex line feed altogether by printing the pathways of both amp to emitter in the same module as a single circuit board. Just so much easier. GaN even promises to be cheaper than GaAs, so not only will the next generation of GaN AESAs outperform earlier generation of GaAs AESA, they are cheaper, lighter and have less heat.

I am thinking one way of reducing PESA line feed insertion loss is to make the line feeds out of fiber optic but the question is how much signal loss you can incur passing through cables of glass so the transparency of the glass is critical.

The point of having a PESA is that a large single analog amp (TWT, Klystron, Magnetron, etc,.) can generate more power than a whole farm array of solid state mini amps and with enough power to compensate for insertion and receive losses. But the advent of GaN substrates pushes the limits of solid state amps even further so the goalpost to justify a PESA is pushed even further.

This leads to a question why you need that much power in a spectrum warfare environment that is increasingly rich in passive detection systems, or passive radars, as others might call it, that can detect your search radar through its signals and turn it against you. This is why LPI or Low Probability of Intercept has become more important and this, along with ECM resistance, is favoring AESA, and the very concept that radars must be 'stealthy' as well.

As a side note, strictly talking here of parallel line feed PESA, which is the type you encounter with fighters but also with some others like naval SPY-1. However if you read text books, there is also something called spaced or optical feed PESA, where the transmitter amp projects the signal through the air using a four horn optical feed to the back of the array which acts like a lens. This system is commonly seen with SAM radars like Patriot's MPQ-53, S-300 Flap Lid, HQ-9's HT-233 and others. There is another kind of ESA called FRESCAN or serial line feed PESA, where you have a single serial line feed to all the linear arrangement of elements. Since the feed is not of the same length, each line element will have a varied frequency from the other and this causes the array to steer as the signals goes through the wave slots. For this reason its called frequency scanning. You see this PESA type with both land and naval search radars, and its also fairly common. Just to mention to avoid confusion.
 
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Anlsvrthng

Senior Member
Registered Member
Those losses affect equally both transmit and receive paths. The net effect is that PESA radars have about 5-7 dB higher losses than AESA radars. This itself is significant as typical burn through threshold is only 7 dB.

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Modern PESA radars (Like bars or irbis-e) has dedicate Rx elements on each dipole so the return loss doesn't count.

So the net difference is less than 3 db.

Of course the raytheon wants to sell his stuff, so doesn't compare the technology to the modern examples.

And gimbal/not gimbal is more about the difference in space and mass .
A small , light fighter with a small AESA radar will be in disadvantage against a bigger aircraft with PESA radar from the same generation, simply because the Tx losses are small part in the radar performance calculation.

So, the F-35 will be in disadvantage against the J-11 in the term of radar performance as well. Every dollar that the Lockheed spend for radar development is to decrease this gap, and the Chinese can increase the performance of the radar with way less investment.
 

Tam

Colonel
Registered Member
Various air defense radars. Posted by LKJ86 at the PDF.


This one is the search radar and fire control radars for the HQ-16. Its very different from the naval application or the Russian Buk systems. The radar on the left is the search radar, the other two are dual band fire control radars, I would assume the larger panel to be a C-band and the smaller panel an X-band. The search radar on the left might be an S-band, with a planar array with slots for wave guides, quite possibly having separate linear receiver and transmitter elements behind each guide, making it an AESA.
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A metric wave AESA.

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Could be a Type 305A, an S-band AESA in support of the HQ-9 system.

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UHF AESA?

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Might be a Type 305B, a FRESCAN PESA that operates on the S-band in support of the HQ-9 system.

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Search radar. This has a four horn monopulse feed.

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Tam

Colonel
Registered Member
Probably an S-band target acquisition radar. It may have separate linear receivers and transmitters behind each wave guide, making it an AESA. Like search radars of this type, they only scan in one direction, up and down, the array is rotated mechanically for finding bearing.


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That is likely an HT233 on the left. Forgot what the four on the right are called, but its interesting enough as these are passive radar or passive detection systems, also known as ESM. They don't emit radar on their own, but catch the target radar and use that signal to determine altitude and bearing by comparing the signal against four receivers.


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More of the PDS.

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