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gambit : Any idea why there is a normal mode and an extended mode for the radar? (Range in normal mode is 200 kms for fighter sized targets, and range is 300 km in extended mode.)
The paragraph is difficult to interpret...
http://mod.gov.in/writereaddata/AR_2013/Eng/ch8.pdf
page 106
The radar has a range of 200 Km for 2 sqm target (extended range 300 Km) and azimuth coverage of...
...But am going to hazard a guess.
Note the figure inside the parenthesis 'extended range 300 Km'. It is given without its own target RCS, implying that the same target can be 2 sqm at that range. Not possible.
For any given radar system, if a target is 1 sqm at 100 km range, its RCS will be higher at a nearer range, and lower at a farther range.
1.5 sqm = 95 km
.5 sqm = 110 km
Remember in radar detection, the higher the RCS at the longer range, the better it is for the defender or the air traffic controller.
So am guessing that the sentence meant to say that this 2 sqm target at 200 km range can be reasonably valid at 300 km, albeit at a lower RCS value. From a technical standpoint, and I have edited technical writing in the past in this field, this is not a very good -- in the clarity sense -- sentence.
No radar system is ever perfect but the perfect measure for any system is internal noise, meaning mainly hardware related, anything from materials that made up the capacitor to the copper traces on the PCB to conduct signals. To put it bluntly, the higher the internal noise, the shittier the system.
Outside the system, we have noise that we cannot control, only deal with. Cosmic background radiation (CBR) or ground clutter from cities or weather phenomenons are examples. When I said 'deal with', I do not mean we receive these unwanted signals and cope with them. I mean how good are our
METHODS of dealing with unwanted signals
BEFORE we receive them. With today's highly software dependent systems, it is a combination of hardware and software on how we cope with external sources of noise. All of this already degrade the system even before any signals reaches the target. Even the most advance system from the US and other Western countries lives under this reality.
So right from the start, before we even attempt to detect any body, our system is already degraded by 2 factors: hardware manufacturing imperfections and the methods that we employ to process the return signals.
The third factor is the target itself. No two targets are ever identical, even if we put two 747s or F-16s in the same configs. There will always be minor differences. But now we are talking about a flight of air superiority fighters, F-15s, covering for ground strikers, F-16s, and our system is supposed to have
ALL of them in view at the same time. It is not a good idea to detect the larger F-15s first, and the smaller F-16s a few minutes or even few seconds later. Unfortunately, this happens often in real life, as in real combat. The smaller fighters can hide behind (masked) by the larger fighters, revealing themselves at the last seconds. Or may be flies just a few kms behind. Or may be uses cloud cover.
The problem for the radar designer is how to make compromises with all these factors in play. He can design a system with a reach of 300 km and process all the data from that distance. But then he could be giving the user a lot of ambiguous or even false targets. Do not confuse 'ambiguous' with 'false'. If a target is among the clouds, he can be fully radar visible one second and scintillating (flickering) the next due to clouds. He is a valid and an 'ambiguous' target. A 'false' target would be when the clouds have multiple relfections to produce a target somewhere else.
So what the designer have to do is configure his system to take in all major variables such as internal noise, methods of data processing, and possible and probable types of target, and always the final practical range --200 -- will be less than the ideal range -- 300.
That range is based upon customer's demand: 'I want a radar that will give me at least 90% probability of any target at 200 km.' In other words, at 200 km out, what the pilot/controller sees on the scope have to be at least 90% certainty that there is 'something' at that range/direction/altitude/speed.
The customer can also say: 'The lowest I can go is 50% probability of any target at 300 km.'
With that allowance, the radar designer can add in that extended range capability. It is not a true extended range, as if there is a higher power output, even though this is a technical possibility. That 300 km range capability have always been there, but because of the customer's demand of 90% probability, the practical range of 90% probability for a 2 sqm target is rated at 200 km. Anything beyond that 200 km, and the probability of a target decreases. And if the customer is willing to live with lower probability all the way to 300 km, it is his money and his life.
What is the penalty in extended mode?
Reduced target resolutions:
- Altitude
- Speed
- Heading
- Aspect angle
Increased odds of target scintillation (flickering). Unless it is something like the C-5 Galaxy transport or the Goodyear blimp.
The above explanation is the best guess I can give with that little sentence. But I think I have it.