This is what the F-22 can do

[Guest IguanaKing]

higher freq = shorter wavelenght = smaller antenna

 

 

Who said anything about shorter wavelength? What I was talking about is longer wavelength=lower frequency=mondo HUGE antenna. Some of these antenna arrays stretch for miles. They can detect LO aircraft at MUCH longer distances than other, conventional radar....the problem is that the accuracy of the return is not good enough to target a weapon to, and "tracking" is a joke. All it does is give the radar operator the opportunity to say, "Yeah...there's something out there...Exactly where? I have no idea. :doh: " Oh...and did I mention that the antenna was HUGE? ;) This kind of rules out any kind of mobility for that radar.

[nscode]

Who said anything about shorter wavelength?

 

I thought you did :D nevermind... I better choose between reading forums and reading physics, cause if I continue like this I won't get anything good from any of them :D

[Guest IguanaKing]

Heh...NP, dude. Its pretty common for me to lose track of discussions also. Especially since my other scientific passion is of a biological nature.

[nscode]

ok... call me if you need some iguana trackers :D

[Guest IguanaKing]

Will do, man. You wanna try and tag one of these beaties with a locator? All I can say is...in the words of Steve Irwin..."Danger...danger...danger." With the Oz accent of course. :D

[Crusty]

Iquanaking..

I apologise...My first post was in badly thought out and my second was a girlish tantrum

[Weta43]

'The first Microwave Laser was constructed by Towens and Shawlow (1954).

Construction:

Beam of ammonia passes through an electrostatic focuser to separate out molecules in the upper quantum state.

Mode of working:

Physical separation was accomplished in the first microwave laser by projecting a beam of ammonia molecules through a system of focussing electrodes which generate a quadrupolar cylindrical electrostatic field in the direction of the beam. Molecules in the lower quantum state experience an outward force and rapidly leave the beam, those in the upper quantum state see a radial inward (focussing) force and eventually enter the cavity. When microwave power of the appropriate resonant frequency (24 GigaHertz) is passed through the cavity, amplification occurs due to the population inversion. If the output power emitted is sufficiently large, self-sustained oscillations results and the input beam is no longer required. When it is operating beyond this threshold the internal losses are compensated by a large enough gain and the device behaves like an oscillator. '

from:

http://library.thinkquest.org/C007258/Microwave_Laser.htm

 

Microwave 'laser' beam - narrow, no spread.

 

Lowering RCS with increasing frequency is a problem for radar that is worth discussing in its own right, but because I'm obsessive I'll just repeat it has nothing to do with the idea I brought up....

 

:-)

 

The technology would need more development than lidar at this time, but it is possible to create a narrow, coherent maser beam.

Also - I talked to en ex RAF radar technician I know & he seemed to think it quite possible to form a narrow microwave beam & effectively sheild the generator so that operators & those not directly in front of it would be safe using 'conventional' technology.

Of course anybody between the device & the target (or on the other side of the target) would be in trouble, but that's fairly true of a chain gun as well...

 

& I guess I'm about done

[GGTharos]

Masers are nothing new and ... yes, theyspread. Big time.

The 'Laser' is not about the beam not spreading, it's about the energy coming out of it being coherent. The lack of spread is just a nice side effect of coherence ;)

 

But that in and of itself is limited by physics and you simply cannot prevent it from spreading.

 

As for shielding ... uh. No. Keep dreaming :D

At least, if you wanna move it anywhere ..

[Guest IguanaKing]

Iquanaking..

I apologise...My first post was in badly thought out and my second was a girlish tantrum

 

Water under the bridge, Crusty. No worries. :D

[Weta43]

No they're not are they - first one in operation in 1954.

 

Lack of spread is actually necessary for coherence.

If the waves aren't travelling on parallel paths their phase relationships will change, & they won't be coherent. Parallel paths don't diverge.

 

There may be some atphospheric scattering as the beam travels (so to that extent the beam spreads, but not at 30 degrees to the axis as soon as it leaves the unit) & some diffraction around the apperture where the beam leaves the resonator, but all the waves leaving a laser / maser more than a wavelength in from the edges of that aperture will leave parallel & continue that way till they interact with something.

[pho3nix]

Spatial divergence is not a function of light coherence.

 

Spatial divergence is a function of the cavity configuration.

 

hence it is the cavity that defines the output beem not the wavelength bandwidth

[Weta43]

(A laser) 'beam may be highly collimated, that is, having a very small divergence, but a perfectly collimated beam cannot be created, due to the effect of diffraction. Nonetheless, a laser beam will spread much less than a beam of incoherent light. The distance over which the beam remains collimated increases with the square of the beam diameter, and the angle at which the beam eventually diverges varies inversely with the diameter. Thus, a beam generated by a small laboratory laser such as a helium-neon (HeNe) laser spreads to approximately 1.6 kilometres (1 mile) in diameter if shone from the Earth's surface to the Moon. By comparison, the output of a typical semiconductor laser, due to its small diameter, diverges almost immediately on exiting the aperture, at an angle that may be as high as 50°. However, such a divergent beam can be transformed into a collimated beam by means of a lens. In contrast, the light from non-laser light sources cannot be collimated by optics as well or much...It should be understood that the word light in the acronym Light Amplification by Stimulated Emission of Radiation is typically used in the expansive sense, as photons of any energy; it is not limited to photons in the visible spectrum. Hence there are X-ray lasers, infrared lasers, ultraviolet lasers, etc. Because the microwave equivalent of the laser, the maser, was developed first, devices that emit microwave and radio frequencies are usually called masers In early literature, particularly from researchers at Bell Telephone Laboratories, the laser was often called the optical maser.'

 

Which I take to mean that a laser (maser - same thing) with a large diameter resonator & apperture relative to the wavelength will produce a relatively non-divergent beam.

[pho3nix]

I agree Weta43, but coherence from what i understood from your post was in conflict to the actual meaning of coherence (consistant phase relationship over time, or distance)

The relationship of diffraction limmited optics is what you are talking about not the relationship between coherence length and gaussian diffraction limit.

For example i have made a fibre laser with a bandwidth of over 20nm thus a coherence length of micrometers and another fibre laser with a 10kHz linewidth which has a coherence length of ~ 30km.

Both have a aperature of ~10 micrometers and suffer the same divergence due to the numerical aperature hence a relatively large colimation beamwidth as compared to a bulk-optic type laser.

[Weta43]

pho3nix, I'm not big on this, basically I'm working it out as I go along..but ..

coherence - 'consistant phase relationship over time, or distance'

for two waves starting from two spatially separated points to maintain a constant phase relationship over space & time they have to be collimated - parallel, otherwise they travel different distances move between where the beam starts out & where it ends & their phase relationship changes.

They start out collimated (non divergent) as they transition from inside the propagating device to outside & then 'The distance over which the beam remains collimated increases with the square of the beam diameter, and the angle at which the beam eventually diverges varies inversely with the diameter.'

So it seems to me that the beam from a maser with a resonating chamber & aperture both many orders of magnitude larger than the wavelength of the radiation will produce a beam that should stay collimated for a considerable distance (& we're only after ~ 160km here, not to the moon) & diverge relatively slowly.

There will be gaussian diffraction around the edge of the aperture, but the intensity of that will fall way within a few wavelengths of the edge that caused the diffraction - no?

 

Basically where I was trying to cover both bases at once.

GG & IK both feel it is impossible to generate a narrow, nondiverging beam of microwave energy & I couldn't see how it was different to any other electromagnetic wave other than in wavelength - which means you should be able to propogate one, it's then a question of how much it scatters in the atmosphere. However much that is I can't see it scattering the beam at 30 degrees to its alignment as soon as it leaves the device (which was part of their objection - that the beam would spread so fast it would fry the operators standing alongside.)

[GGTharos]

The reason is the method of generation. You're likely looking at a number of waveguides and generators rather than a single one, which can easily be out of phase with each other (in fact, they likely will be) enough to cause beam divergence of that magnitude.

 

Radar beams at 1-2 deg in diameter, radar *missile* beams (smaller antenna) are 6-8 degrees. And those are generated by a single emitter. Think about it ;)

[pho3nix]

Your absolutley right, what i ment was that if you use correcting optics, i mean, obviousley you are not going to use the end of the cavity sticking out of the aircraft, you are going to have some optics in between.

From these optics, if you are trying to get the smallest 'beam waist' the aperature must be large, ie there is an inverse proportionality between beam waist and aperature size that cannot be changed via correcting optics, that what i ment by gaussian diffraction not standard diffraction off an edge (sorry for that confusion)

 

but still, the size of the aperature does not dictate the coherence length of the laser but the cavity and gain medium.

 

Iam not crash hot on masers but i belive that their linewidth is not very narrow due to the mechanism of rotational excitation of the NH3 bonds (dont quote me on that)

 

Every thing you have said is 100% but do a little reaserch if you like on coherence length and how it is defined interms of lasers and you should find that the coherence length is a function of the bandwidth only as if you think about what happens when you mix waves of differnt frequencies together, superposition dictates that the waves will mix in time space and remain seperate in frequency space thus causing a phase defect.

 

i know this may not bee excactley on topic but it is good to clear these things up :)

 

I realy encourage you to persue this further as it is a very interesting type of physics to understand :)

 

EDIT: And yes electromagnetic radiation of any type still obeys the same laws

[S77th-GOYA]

Here you go, boys. Have another. :D

[Pilotasso]

why people cant just use ONE thread? Its complicated to visit 3 of the same subject.

[Force_Feedback]

Yeah, let's make this one the longest.

 

BTW, about the Tu-160 ECM, in some Russian documentary it was said a mig-31 couldn't get a lock, let alone launch a radar guided missile, while flying behind it within visual range :P

[Groove]

Story taken from http://www.af.mil

 

any questions ?

[GGTharos]

Yeah, let's make this one the longest.

 

BTW, about the Tu-160 ECM, in some Russian documentary it was said a mig-31 couldn't get a lock, let alone launch a radar guided missile, while flying behind it within visual range :P

 

Same is said for B-52's. You can launch a missile, it just won't go anywhere near the plane.

[nscode]

One more reason for ET :)

[Pilotasso]

Same is said for B-52's. You can launch a missile, it just won't go anywhere near the plane.

 

I have heard it about the B-1 but never on the buff. It would need shear electromagnetic power for that. It would cause you to "shoot blanks" from then on. :D

[bflagg]

Cool pic of the '22 on approach...

 

Pair of 22's on approach

[cool_t]

Sorry

 

Please prove me wrong but,

 

PHOTOSHOP? or somthing of that nature.

 

:detective: