PLA AEW&C, SIGINT, EW and MPA thread

[crobato]

I wish people need to learn more about radars.

Power is not the main factor in range. Frequency is. A low power signal can travel hundreds and even thousands of kilometers if the frequency is long enough to reduce atmospheric attenuation. However, what long frequency requires is a big antenna, since each element has to be at least 1/2 the length of the frequency. You can bounce radio signals off the moon with a ham radio.

The second determinant of range is the length of the receiving time. That means the radar has to wait for the receiving signal to come back. If the radar has to broadcast a second signal before the echo of the first signal is received, the echo of the first signal is then lost. So the radar has to wait. The longer these wait times, the longer the range. The disadvantage of this, the longer your wait times are, the less signals you can broadcast over time, which means lower resolution in terms of tracking and discrimination.

Any radar that is looking for a balance between range, tracking and discrimination needs to find a sweet spot in frequency and pulse times, basically PRF. Its just physics. You want longer range, you're going to suck when it comes to tracking and discrimination. You cannot expect a detection range of 1000km to have the discrimination and resolution rate you get with 300km.

The result is that all radars have various operating modes that has to bias the radar either for longer range detection, to shorter range tracking and discrimination.

 

[RedMercury]

A question about PRF: say if the radar sent a second pulse out after 1/2 the expected round trip time of the maximum range target it hopes to track. In the event of a radar return, there is two possible ranges: either the first pulse reflected at some range, or the second pulse reflected at some shorter range. Or if you send 3 pulses during the expected round trip time, you get 3 possibilities. For a small number of possibilities, you can use a tracking algorithm to disambiguate. I'm sure radars use adaptive PRF, and with AESA I would imagine individual TR modules can have their own PRF. So it seems to me the PRF isn't as big of an issue as the wavelength and atmospheric attenuation.

 

[tphuang]

well, it's sad that they only have 4 in service
来源：新华社
新华社北京９月２４日电（记者孙茂庆、王东明）国庆６０周年阅兵空中梯队指挥部总指挥、空军副司令员赵忠新２３日透露，这次阅兵空中梯队领队机，由我国自行研制并正式装备空军的大型预警机担任。

　　赵忠新说，这型国产预警机集空中指挥、预警探测、电子对抗等多种功能于一身，是空军信息化建设和装备发展的重要成果，有“空中指挥所”之称，是空军实现攻防兼备战略转型的标志性装备，也是空中作战体系能力的关键要素，代表着近年来空军信息化建设的新成就。

　　赵忠新介绍，目前，空军预警机已形成了战斗力，在日常防空战备以及奥运空中安保中发挥了重要作用。
talks about KJ-2000 here I think. Says that it combine aerial command/control, early warning and ECM and other functions in one body. It says it has achieve operational capability and was very important in the Olympics.

 

[Hyperwarp]

well, it's sad that they only have 4 in service
来源：新华社
新华社北京９月２４日电（记者孙茂庆、王东明）国庆６０周年阅兵空中梯队指挥部总指挥、空军副司令员赵忠新２３日透露，这次阅兵空中梯队领队机，由我国自行研制并正式装备空军的大型预警机担任。

　　赵忠新说，这型国产预警机集空中指挥、预警探测、电子对抗等多种功能于一身，是空军信息化建设和装备发展的重要成果，有“空中指挥所”之称，是空军实现攻防兼备战略转型的标志性装备，也是空中作战体系能力的关键要素，代表着近年来空军信息化建设的新成就。

　　赵忠新介绍，目前，空军预警机已形成了战斗力，在日常防空战备以及奥运空中安保中发挥了重要作用。
talks about KJ-2000 here I think. Says that it combine aerial command/control, early warning and ECM and other functions in one body. It says it has achieve operational capability and was very important in the Olympics.

Is this because of the shortage in Il-76 airframes? Could this change if the Il-76 deal gets through? Or is there a another reason? I don't expect the KJ-2000 RADAR to be cheap in anyway.... Probably costs a !@#$^

 

[challenge]

Is this because of the shortage in Il-76 airframes? Could this change if the Il-76 deal gets through? Or is there a another reason? I don't expect the KJ-2000 RADAR to be cheap in anyway.... Probably costs a !@#$^

why only 4 were build? correct me, a standard squadron needed 12 aircrafts.
few years ago, chinese web site report that PLAAF official complain KJ-2000 high maintainance cost.speculation that PLAAF may be looking for alternative platform ,likely a 2 engine AWACS. like israel G550 or 767-AWACS operate by JSDF.
or something between KJ-200 and KJ-2000.

 

[crobato]

A question about PRF: say if the radar sent a second pulse out after 1/2 the expected round trip time of the maximum range target it hopes to track. In the event of a radar return, there is two possible ranges: either the first pulse reflected at some range, or the second pulse reflected at some shorter range. Or if you send 3 pulses during the expected round trip time, you get 3 possibilities. For a small number of possibilities, you can use a tracking algorithm to disambiguate. I'm sure radars use adaptive PRF, and with AESA I would imagine individual TR modules can have their own PRF. So it seems to me the PRF isn't as big of an issue as the wavelength and atmospheric attenuation.

The length of the PRF alone gives you a direct fix on the range of the target. Its impossible to have faster PRF on longer ranges because PRF is fixed by Einstein---the speed of light. In your example, if the radar sent out a second pulse while waiting for the first pulse, then all is screwed because the radar needs to distinguish which pulse is which. That's why there is a wait period, because the radar knows the pulse it is receiving is the one last it sent out. If a pulse that was sent out earlier, echoed against a much farther target, then received by the radar which is also receiving other echoes simultaneously, it would be disregarded. The radar will only accept the echoes of the last pulse as valid.

In other words, the PRF interval is the range of the target divided by the speed of light x 2.

Myth about electronic scanning. For electronic scanning to work, all pulses have to be synchronous, with some pulses have to be sent out in with phased latency offset (some sooner some later). The pretimed offset of one emission causes the emission next to it to bend a bit, which in turn causes the one next to it to also bend, via interference. By changing the offsets, you have controlled constructive and deconstructive interference, which causes the beam to shift. Individual modules cannot have their own PRF because alone, each individual transmitter is incapable of shifting beam direction without an entire row, set, or face of shifters working together.

 

[FriedRiceNSpice]

Pardon me if my physics is a little rusty, but if multiple pulses were sent out, wouldn't the echoes and incoming waves also cancel each other out?

 

[Troika]

why only 4 were build? correct me, a standard squadron needed 12 aircrafts.
few years ago, chinese web site report that PLAAF official complain KJ-2000 high maintainance cost.speculation that PLAAF may be looking for alternative platform ,likely a 2 engine AWACS. like israel G550 or 767-AWACS operate by JSDF.
or something between KJ-200 and KJ-2000.

Hell no. AWACS on the E-3 level do NOT operate in squadrons of that size. 4 aircrafts is actually a decent size for a squadron. 6 would be even better.

But 12's more like a mini wing.

 

[pla101prc]

Hell no. AWACS on the E-3 level do NOT operate in squadrons of that size. 4 aircrafts is actually a decent size for a squadron. 6 would be even better.

But 12's more like a mini wing.

lol the americans prooly have no more than 20 E-3's right now

 

[Totoro]

lol the americans prooly have no more than 20 E-3's right now

While they do have 'just' 32 E3s (maybe down to 31, there was an accident with one plane some weeks ago), to that figure one should add 68 E2s as well. While they are under Navy's command, one can rest assured they'd be used from fixed runways if needed.

On top of that, in the unlikely case of a NATO led operation, there are, not counting the help of other NATO member's awacses, additional joint force 17 E3s, under joint NATO command, independant of any one particular country.