Chinese Radar Developments - KLJ series and others

Zichan

Junior Member
Registered Member
In the other hand, air cooling is easier to implement, light and may have little impact to the aircraft's structure, thus why those AESA upgrades for legacy fighters are typically air cooled.
This a bit of an apples and oranges comparison. To dissipate an equal amount of heat, an air cooled solution will need more weight in radiators near the antenna, whereas liquid cooling offers much more flexibility in the location of radiating surfaces.
However the main driver of AESA performance would be number of TRM's as the performance gain, scales by cube of TRM. Radar that can pack more TRM's than the other will usually "win" in terms of performance. Radar with less number of TRM's when trying to match the performance of the radar with more TRM's will be "penalized" in cooling and power requirement and thus cost.
With the important simplifying assumption that the TRMs and backend signal processing are the same. More TRMs mean a larger antenna aperture, power and gain, which is why the PA product is a useful yardstick for comparing radars of similar tech levels.

However, state of the art AESAs with wide bandwidth, digital beamforming and more sensitive receivers can easily have superior performance over older analog AESAs from the early 21st century, especially once environmental factors like jamming are brought into the picture.
 

Stealthflanker

Senior Member
Registered Member
This a bit of an apples and oranges comparison. To dissipate an equal amount of heat, an air cooled solution will need more weight in radiators near the antenna, whereas liquid cooling offers much more flexibility in the location of radiating surfaces.

The more important thing is the cooling capacity it provides. There is no "Moral ground" here for "apples and oranges" But rather it's clear..you want power go liquid, you want light and easy, go air cooled. If you need more power for your Air cooled Radar, then pack as many TRM as practical.

However, state of the art AESAs with wide bandwidth, digital beamforming and more sensitive receivers can easily have superior performance over older analog AESAs from the early 21st century, especially once environmental factors like jamming are brought into the picture.

Define bandwidth as you will have several types of bandwidth here :

1.Your operational antenna bandwidth or fractional bandwidth which refers to the frequency that you operates in.
2.Your receiver bandwidth, which based on your emitted pulsewidth and also depend on what target you are trying to engage.

The #1 is defined in your operational regime. and for current AESA Which still relies on Phase shifters it is about equivalent of your beamwidth and limited by beam squint phenomenon. We have no real "True time delay" AESA yet and this is 21st century.

#2 Cannot be changed arbitrarily, if you do calculation on MDS (Minimum Detectable Signal) You will notice "smaller" receiver bandwidth lead to "more sensitive" receiver but as you find out, too small of a value indicating an inoperative receiver. While "larger" bandwidth lead to "less sensitive" receiver.

Related to DBF is that i wonder if any fighter aircraft radar already operate such DBF ? AFAIK Only Japan so far experimenting with it.
Maybe it is the "real thing" once the real practical and cost effective means of Element level DBF become available. RIght now however we are living in your so called "Analog" AESA.

As for sensitivity well. Define sensitivity too as Loop gain which previously you have difficulty in accepting as a real proper metric to define sensitivity and also scales up with increase in TR count as seen in US SPY-6 Radar... you still not understand eh why the "dB" figure increase as soon as you add more module.


For jamming however It is beyond the scope of My modeling and RRE as some jammers does not really attack the capability of a radar to determine range. One thing however is that the AESA does not seem AFAIK to offer new technique. Other than Adaptive nulling which can help deals with noise jammer. While others like leading edge tracking to counter VGPO and RGPO can be implemented in other radars.

Also for angle tracking, what AESA you think do angle tracking with other methods than Monopulse ? Current Radars are using Monopulse angle tracking method, particularly Amplitude Comparison. There are others namely Phase Comparison but this is rarely used in fighter or ship or any Radars other than niche application like counter battery and to some extent ABM Radar.

Monopulse itself are vulnerable to Cross Eye jamming which still the most effective, Cross Pol and Image frequency jamming are also available but Cross Eye would be the hardest to counter. What you think AESA might offers in countering that technique ?
 

Zichan

Junior Member
Registered Member
My last remark on the cooling: with liquid cooling a large chunk of the aircraft fuselage could be used as a radiating surface: in essence you get a big, if inefficient radiator for free. At some point, it will simply scale better than air cooling even on a weight basis.

I almost exclusively follow naval radars. I‘be seen that HENSOLDT is aiming for a fully digital fighter AESA for the NGF in the 2030 timeframe.

What I know is that the SPY-6 radar is already a fully digital AESA (in S-band). This means independent control of each transmit element and independent analog to digital sampling at each receive element. Beamforming is done digitally. On the receive side, as many beams as necessary can be generated using computational post-processing techniques on the digitally sampled RF signals. This means vastly superior scan rates and ability to track significantly more targets compared to analog beamforming solutions, like the F-22 AESA radar or the SPY-1 PESA. Analog beamforming is limited by the resolution of phaseshifters in a way that DBF is not.

Furthermore, DBF by virtue of creating sub-beams provides super-resolution in azimuth and elevation. Combined with wide-bandwidth that allows submeter resolution in range and a powerful target discrimination capability. Such radars can create detailed 3D target maps and guide radar or IR guided missiles towards actual threats, instead of decoys.

Because each element in the array is coupled to a dedicated ADC, the dynamic range of the array is vastly increased. Compared to an analog array of say 1000 elements with one ADC, a digital array with 1000 ADCs will have a 1000 times greater dynamic range.

To deal with jamming and clutter, digital radars use various techniques like Space Time Adaptive Processing for example which allows the radar to single out the jammer signal arrival angle in post-processing and nullify it.
 

Tam

Brigadier
Registered Member
My last remark on the cooling: with liquid cooling a large chunk of the aircraft fuselage could be used as a radiating surface: in essence you get a big, if inefficient radiator for free. At some point, it will simply scale better than air cooling even on a weight basis.


This part only makes you more vulnerable to IR based detection and tracking methods, including those with IR guided missiles.
 

taxiya

Brigadier
Registered Member
Related to DBF is that i wonder if any fighter aircraft radar already operate such DBF ? AFAIK Only Japan so far experimenting with it.
Maybe it is the "real thing" once the real practical and cost effective means of Element level DBF become available. RIght now however we are living in your so called "Analog" AESA.
Radar of KJ-500 is fully digital meaning it is DBF. I don't know of any fighter sized aircraft. Anyway, it is the first full digital airborne AESA in operation reported.
 
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