In my memory, a journal indicates if the canards parallel to the main wings, it will cause huge RCS.
Not necessarily true. We have gone thru this before on this forum...
There are three main rules in designing a radar low observable body:
- Control of quantity of radiators
- Control of array of radiators
- Control of modes of radiation
They are not necessarily rules that can be violated. Rather, they are more like guidelines that indicate the degree of obedience to them.
The F-22 has six major flight controls structures. The J-20 has eight. That make the J-20 less obedient to Rule 1. But that does not automatically make the J-20 more visible EM-wise. It forces the engineers to focus on Rule 2.
Rule 2 is what make observers, many of them experts in the field, suspicious of the J-20's canards regarding trying to be as low radar observable as the American fighters.
The canard is a finite body, meaning at some time and somewhere, the radar signal has to leave this structure. How the exiting signals make contact with the other structures is what make the canard detrimental to 'stealth' or not a factor at all. But based upon the current understanding of signal behavior, the J-20's canards with their dihedral is at least suspect to be detrimental to the J-20's attempt to be as 'stealthy' as the American fighters as in Rule 3.
All three rules must work together and this is evident with the
UPPER surface of the F-117...
Each 'ridge' is an exit point for an impinging radar signal. So under the three rules, the F-117 has many more structures than the J-20. Lockheed engineers paid close attention to how the three rules interact with each other and the result is that the F-117's RCS is still a secret. Everyone, including China, would love to know that figure. In some ways, the US have been more open with the F-117's RCS than China has with the J-20's RCS. Ben Rich's book at least hinted at that figure.
http://www.f117sfa.org/f117_history.htm
The model was mounted on a 12-foot high pole, and the radar dish zeroed in from about 1,500 feet away. The site radar operator could not see the model on the radar, until a black bird landed right on top of the Hopeless Diamond. The radar was only picking up the bird....
This is why the criticism about the F-35's underside with all the bumps as detrimental to 'stealth' is nonsense. The critics cannot reconcile the F-117's topside and the F-35's underside. As if somehow the laws of physics behaves differently for each jet.
For now, conventional wisdom has it that being parallel in the root plane and no dihedral is ideal. The J-20's canards is one half of that conventional wisdom. Their roots are on the same plane as the main wings, but their dihedral affects how exiting radar signals contact the main wings in terms of direction, angle of approach, and distance.
