ata wrote:. The main characteristic of ANY antenna in the world will be it's GAIN. For exampl
e aperture is absolutely unimportant because aperture in general only define gain.
You can create huge aperture antenna, but if it's gain will be low, then such a size just useless. So, what in fact gain means? Frankly speaking it's how wide or thin antenna's beam. Of course it's not a definition (there are lobes, losses etc), but it's enough to understand the idea.
Look at this:
http://www.aktivsb.ru/article-info1499.htmlCompare left and right patterns at first picture. At right side antenna has very low gain because it transmit power to whole world in front direction. At the left side gain is much higher because it only sends signals in one thin beam (skip the lobes at the moment). All the power just in one point. Why is it important? Because in case of radar: LPI, non-LPI, no matter what engineers try to create the thinest reasonable beam possible. To bring all the available power in one point.
Beamwidth varies directly with wavelength and inversely with antenna size for example : if operating frequency is 1 ghz and antenna is 1 meter then the beam width will be 25 degree ( same reason why the T-50 wing edge thing is not a radar but only a IFF system ) , inversely if the antenna is 10 meters in dimension then the beam width will be 2.5 degree
Higher wavelengths allow a smaller antenna to have the same gain.For example, at X Band (3 cm); you need an antenna 45” in diameter to get a gain of 40 dB; while at S Band (10 cm); you need an antenna 150” in diameter to get the same gain of 40 dB.
http://www.alternatewars.com/BBOW/Radar ... istics.htmata wrote:Do you remember I've calculated that at 100 km 2 degrees beam will give you 3,5 km spot? It's not exactly truth. It will be even bigger, but normally this kind of sizes measured at -3db, -10 db levels (it's all depend of agreement and standards). That size's spot will be about 10 sq. km. while Flanker size object (not it RCS) actual size will be about 10 sq. m. So only 1/1 million part of your energy will make sense. All the rest you spent to heat up atmosphere.
the part that spend heat up the atmosphere doesnt get intercepted by Su-35 sensor either

, and Su-35 doesnt have radar receiver all over it's body but only very few part , accounted for less than 0.1% of it's surface area , as a result

of all the signal come to Su-35 direction, only 1/1 million part will hit it's airframe , and 1/1000 will hit it's RWR antenna
ata wrote:The another theory. What electro-magnetic reflection means? Again, frankly speaking incoming wave generates some electric current in metal shape, and that current generates electro-magnetic field in back (this is very simplified theory, because for example dielectric materials also reflect some radio waves). In fact your target acts like secondary oscillator. The only difference it will transmit it's power in every direction. Let's say in every direction in the same level
wrong , if that was the case then it would be impossible to designed any stealth fighter , and all fighter of similar size will have equal RCS in all direction
ata wrote:. Let's calculate how big is your radar (1 m in diameter) from 100 km far away for antenna with 0 db gain.
Approximately it will be 1/4*10ˆ-11
We also have to remember about initial 1/1 million part of energy. Finally you'll get 1/4*10ˆ-17. It's -164 dB. While at target side it's just -80 dB
(because Flanker's radar has approximately 1 sq. m size as well). About 80 dB difference.
Wow, isn't it? In fact because I simplified the idea (to show the origin of such high loss) it's not exactly correct. Look at this:
http://www.radartutorial.eu/01.basics/T ... on.en.htmlFunction (9) shows that received power is 1/Rˆ4 function (because antenna gain, RCS, transmitted power are constants). Even if you have 40 db antenna gain (which seems not really possible) and squared it's just 10ˆ8. If you have relatively high RSC it's another 10ˆ1. Even in that case it will be still 10ˆ-11 of transmitted power. While at target side it will be 10ˆ-5.
So, Flanker radar operates in fact not thousands, but million times higher signal level than that at F-35.
unlike RWR , radar only intended to receive it's own signal , if the flanker radar treat all signal it received as a target , then the radar screen will be clutter with thousand targets made by deceptive jammer , Irbis-e will be super easy to fool
ata wrote:So, if F-35 is able to detect it's signal from the noise why do you think it's a problem to do with million times better option (noise level is the same for both sides)? Yes LPI switches frequencies, but it's not like "from any to any" those peaks are still in X-band. And because Flanker radar is also X-band it will receive all of them. We can talk about fighting with the noise but believe me dealing with noise is huge part of radio tech and I need to take all my old books from the shelf to remember all the stuff. It's well known problem and it's discovered from the first phone-line in the world.
If you have any application to generate spectrograms for sound files try to do the following. Generate the file with several very short peaks with different frequencies. It will emulate LPI. Then apply some noise (it's possible with apps like SoundForge). Even you can do noise level similar to peaks level. Then generate spectrogram. It should look like this:
http://audiophilesoft.ru/articles/quali ... fhg320.jpgAt your picture you'll see small bright dots - these are your peaks. If you can see it with your eyes, then it's possible to create algorithm to detect it. This is how LPI works.
As you said your self before , only a small part of energy from APG-81 hit the Su-35 , the rest heat up the air , hit the ground ..etc
How do flanker RWR discriminate between the signal come from APG-81 direction it's self and the signal from APG-81 that hit the ground , or bird first before reflected to the Flanker ?
And as i explained , since RWR cannot compute the distance to an moving air target so even if RWR on Su-35 some how detect APG-81 , the only information the Su-35 pilot will know is the direction that F-35 come from

, no distance , no speed he cant attack it , and we back to low band radar problem , only helpful for early warning