gambit
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A question was asked about the possibility of a moving-target-indicator (MTI) radar to detect F-117 class bodies. The answer is 'Yes' but with serious caveats.
First...There is a misleading argument bandied about that goes: Since the F-22 has the RCS of a bird and no bird flies at several hundreds km/h, the US wasted a lot of money for nothing.
The argument is flawed in the fact that all radar systems have what is called the 'clutter rejection threshold', meaning stuff that are detected but whose electrical characteristics are known and filtered out. These stuff include cosmic background radiation, music radio, or TV signals. The classical concave dish just make their detection directional. All radars detect these things and installed filters raises that 'clutter rejection threshold'. Birds are usually filtered out so even if the 'bird' flies at Mach 10, it will be filtered out from the start.
Which lead up to the next point...
The above is an illustration of a typical radar signal.
There are four main very important characteristics:
- Amplitude
- Freq
- Pulse duration (or width)
- Pulse Repetition Interval
A series of pulses interrupted is called a 'pulse train'. We can change the above four characteristics from train to train but that is for another discussion.
From these four items we receive vital target 'resolutions' such as speed, altitude, heading, Doppler, and aspect angle. The last meaning how is the target facing us.
For an MTI radar, it is the Doppler component that is of interest. What an MTI radar does is to focus its data processing only on the Doppler shifts of a moving target. It does not care of heading, altitude, or aspect angle...
Doppler radar - Wikipedia, the free encyclopedia
So for an MTI radar to be used against an F-117 class body, we would have to lower that 'clutter rejection threshold' to detect bodies smaller than birds then process EVERY SINGLE Doppler components of EVERY SINGLE moving bodies within the beam. Even with data processing of only one component out of many, the processing demand of so many objects is a serious technical hurdle. We can reduce this burden by narrowing the beam but this would increase coverage time over any given airspace volume. Then if some birds or a flight of F-35s just happened to be across our radar view instead of approaching or receding, the MTI system would not process them at all.
For the defender, there is another serious tactical disadvantage when facing a radar low observable adversary...
The B-52's RCS and its Doppler component will dominate the search volume and will mask the far smaller B-2's RCS and its Doppler component. Not completely but just enough to make an effective distraction and draw vital airborne resources to investigate. What if a flight of real birds take flight? The MTI radar could process different birds at different locations to be the one that flies at several hundreds km/h. More vital resources to investigate real birds instead of the one that matter.
So is an MTI radar an effective detector of an F-117 class body? Only if the conditions are 'just right'. But a knowledgeable adversary will do his best to create as 'wrong' the battlefield conditions as possible to maximize his technical advantage.
First...There is a misleading argument bandied about that goes: Since the F-22 has the RCS of a bird and no bird flies at several hundreds km/h, the US wasted a lot of money for nothing.
The argument is flawed in the fact that all radar systems have what is called the 'clutter rejection threshold', meaning stuff that are detected but whose electrical characteristics are known and filtered out. These stuff include cosmic background radiation, music radio, or TV signals. The classical concave dish just make their detection directional. All radars detect these things and installed filters raises that 'clutter rejection threshold'. Birds are usually filtered out so even if the 'bird' flies at Mach 10, it will be filtered out from the start.
Which lead up to the next point...
The above is an illustration of a typical radar signal.
There are four main very important characteristics:
- Amplitude
- Freq
- Pulse duration (or width)
- Pulse Repetition Interval
A series of pulses interrupted is called a 'pulse train'. We can change the above four characteristics from train to train but that is for another discussion.
From these four items we receive vital target 'resolutions' such as speed, altitude, heading, Doppler, and aspect angle. The last meaning how is the target facing us.
For an MTI radar, it is the Doppler component that is of interest. What an MTI radar does is to focus its data processing only on the Doppler shifts of a moving target. It does not care of heading, altitude, or aspect angle...
Doppler radar - Wikipedia, the free encyclopedia
The highlighted is a serious drawback when a radar system is purposely designed to process only the Doppler component of a moving body.
So for an MTI radar to be used against an F-117 class body, we would have to lower that 'clutter rejection threshold' to detect bodies smaller than birds then process EVERY SINGLE Doppler components of EVERY SINGLE moving bodies within the beam. Even with data processing of only one component out of many, the processing demand of so many objects is a serious technical hurdle. We can reduce this burden by narrowing the beam but this would increase coverage time over any given airspace volume. Then if some birds or a flight of F-35s just happened to be across our radar view instead of approaching or receding, the MTI system would not process them at all.
For the defender, there is another serious tactical disadvantage when facing a radar low observable adversary...
The B-52's RCS and its Doppler component will dominate the search volume and will mask the far smaller B-2's RCS and its Doppler component. Not completely but just enough to make an effective distraction and draw vital airborne resources to investigate. What if a flight of real birds take flight? The MTI radar could process different birds at different locations to be the one that flies at several hundreds km/h. More vital resources to investigate real birds instead of the one that matter.
So is an MTI radar an effective detector of an F-117 class body? Only if the conditions are 'just right'. But a knowledgeable adversary will do his best to create as 'wrong' the battlefield conditions as possible to maximize his technical advantage.
