There WILL BE NO tactical advantage gain for the PLAAF with the J-20 even if the J-20 does have some technical advantages. Here is why the J-20 and the Su-57 are DOA.The F-22A has been the best fighter in the world for two decades, but it would not be surprising that the J-20 has advantage in some areas.
The below is a simplified visual explanation of how radars sees any body...
...As a CLUSTER of voltage spikes.
The below is a more sophisticated visual representation...
The higher the operating freq and the more refined the data processing of the reflected signals, the more complex the final display.
Even if the reflected signals are 'stealth' meaning amplitude (strength) is low enough to blend/mask with background radiation, the CHARACTERISTICS of the reflected signals are still evident. The first character is amplitude, which is low enough to be filtered out by most radars. The second character is that clustering or grouping of signals. More detailed characters about the body are revealed by the radar pulse characteristics but we can leave those alone for now.
What is significant is that general types of bodies produces recognizable cluster signatures. A sphere would not produce a complex cluster like the above visual representations. A cube would also not produce complex signal clusters but the cube would produce a different cluster signature than the sphere. We have baseline library of simple shapes for decades.
Radar cross section (RCS) methods for simple shapes are reviewed with special attention being devoted to results rather than to derivations of the formulas involved. In addition, special emphasis is placed on an approach which can be extended to "complex" shapes. Where possible, comparisons...
Radar cross section (RCS) methods for simple shapes are reviewed with special attention being devoted to results rather than to derivations of the formulas involved. In addition, special emphasis is placed on an approach which can be extended to "complex" shapes. Where possible, comparisons between theory and experiment are provided to give a measure of the accuracy obtainable via the use of these techniques. The discussion is limited to perfectly conducting bodies: in particular, ellipsoids, finite cones, ogives, cylinders, thin wires, wire loops, and flat plates. An attempt is made to cover the complete spectrum of body dimension to wavelength ratios; that is, the Rayleigh region, the resonance region, and the optics region are all considered from the points of view of both monostatic and bistatic phenomena.
A Rolls Royce cluster of signals would not be identical to a farm tractor but both clusters would have parallel characteristics. If the discrimination does not care if the clusters are Rolls Royce and John Deere, then the SIMILARITIES would be enough for 'other' purposes.
A major problem with most RCS calculations is that the seeking radar is usually static meaning ground based. Then the target aircraft is flown within the seeking radar beam. We already know that as aspect (viewing) angles changes, the reflected signals changes in terms of cluster amplitude and complexity. By the seeking radar being fixed on the ground, we have incomplete signal knowledge of the target. Airborne radars are not new but they are limited in construction due to aviation limitations such as size, weight, and aerodynamics.
Enter the RATT55...
This modified 737 is even more secret than the next 'stealth' platform.
Nobody knows exactly where “Rat 55" lives or precisely what technology it uses to accomplish its mission, but it sure is an exotic beast. The USAF’s secretive NT-43A testbed is a highly modified 737-200 that goes far beyond ground-based radar and infrared signature testing on stealthy aircraft...
The NT-43A radar aircraft testbed (probably where the “Rat” call-sign comes from) is most likely the last stop in advanced low-signature testing and validation for new stealthy aircraft, new radar absorbent coatings and heat mitigation technologies, as well as exotic and stealthy structural modifications to existing aircraft. In other words, whether it be a whole new aircraft or just a new radar absorbing material applied to an existing stealthy aircraft, the NT-43A evaluates it under realistic flight conditions with its powerful radars and infrared energy detecting devices. Even repairs and depot-level work on existing stealth aircraft may be validated in flight via the NT-43A.
The NT-43A’s massive radars are most likely able to take incredibly detailed synthetic aperture ‘pictures’ of their target aircraft, as well as collecting sensitive ‘raw’ radar measurements and associated data. Its front and rear pods that give the jet such an ungainly appearance allow it to collect radar and infrared data (the IR sensors sit atop the radar fairings) from every angle around the target aircraft in flight without having to fly at oblique angles towards and away from it. The radar system may have some bistatic capabilities when both front and back arrays are used in conjunction with one another.
The highlighted is important. By being airborne, the RATT55 is able to scan the aircraft from multiple aspects (viewing) angles that are mostly cleared of ground reflections that always contaminates the signal set. But that is not all, precisely because all aircrafts produces similar cluster signatures, we now have a base library of common signal characteristics that WILL enable us to extrapolate an unknown signal set.
As if that is not enough...
...an aircraft may have very little radar signature head-on, but at certain angles its radar cross section grows significantly. Once these intricacies are very well documented, the performance of enemy radars, infrared search and track systems and anti-air missile systems can be better theorized. This allows for a much more accurate understanding of how close a ‘stealth’ aircraft can get to different threats without being detected or without being engaged. Mission planners can then build elaborate routes around known enemy air defense systems and give crews good advice on how to present the best aspect of their aircraft to unplanned for ‘pop-up’ threats so that they have the best chance of surviving a mission.
Using what RATT55 produced, US planners can, or more likely HAVE, created exercises with complex EW threats. The great thing about EW exercises is that they are not exercises. There is no need to actually launch a SAM in order to produce a virtual 'kill'. In an EW exercise, an electronic identification of a target constitutes a 'kill', making any EW exercise essentially the real thing. Is there any wonder why we fly all those SIGINT sorties?
The J-20 is Dead On Arrival (DOA) and their pilots do not even know it.