paritosh
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Be careful about this kind of general statement/claim.
NTIA Special Publication 00-40 - Chapter 3
Missile seekers and targeting radars are usually in ghz bands. This is for high target data update. The closer one gets to the target, the more important it is to have this high target data update. If the target make a sudden move, as in evasive maneuvers, only the ghz bands is capable of providing that sudden movement update information.
That mean frequency agility is limited in scope. Everyone know this. So everyone need to pay attention to the paragraphs above, particularly about the physical antenna size and beamwidth relationship. Target data update also improve as the main beam narrows. But antenna dimension inversely affect beamwidth. All the more reasons why frequency agility is limited in scope -- At higher frequencies, small antennas will suffice. So since missile radar seekers have small nosecones, therefore very small antennas, they will have to resort to using the ghz bands IF they want to have that high target data update just in case the victim make a sudden move to evade the missile. Once again -- frequency agility is limited in scope.
But since everyone know this fact, the only thing left for the designer is that frequency agility ability itself, as in how fast can the system move between one freq to another, in transmit, receive and processing of the data. All three items must be ideally balanced. The better this 'jumping' around, the more difficult it will be for the opponent ECM to keep up. The better ECM systems will be able to anticipate, but not with %100 certainty, as to where the next 'jump' will be and saturate that freq as well as the current one. It is very difficult to envision the whole thing since this is happening at practically light speed.
So to sum it up...
Narrow beamwidth is desirable for rapid target data update. Overriding consideration. Utmost importance. No other discussions necessary.
- The lower the freq employed, the larger the antenna.
- The higher the freq employed, large or small antenna will do, but with small missile radomes, it will be small antennas.
thanks for the informative post...there are some points i'd like you to opine on..
i thought we dealt with the limitations posed by the antenna sizes of (limited by 1/4*f) decades back through modulation?
Don't we modulate the em radiation from seekers/radars to make up for the size differences?
i am aware that even if we do...it only helps to an extent the size would be the bigger factor...
but as far as I know...most BVR missiles have different stages of guidance..
in the first stage they are guided by the more powerful radar onboard their mother aircraft...in the second stage they turn on their own seeker which might be passive....seeking em radiation or active....giving out radiation to see the target..
there are different antenna beams for different purposes...a fan beam might be used for searching a target....a pencil beam for tracking...
the forward gain of a fanbeam will be lower to a comparable pencil beam...and would require more power...hence the missile seeker might utilize a pencil beam to track the target in the final moments....
and wouldn't target resolution depend more on prf?
RCs on the other hand would depend on the frequency of the m/w beam...isn't that right?so getting a high prf in the later stages when closing-in on the target shouldn't be much of a problem with a good dsp equipment...right?
don't some of the missiles utilize 2 frequencies to home in?
which they shuttle between...to avoid getting jammed?
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