Author Topic: Laser-like narrow cone of Mhz/Ghz waves?  (Read 822 times)

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Offline cape zoloh

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Laser-like narrow cone of Mhz/Ghz waves?
« on: October 16, 2021, 01:22:53 pm »
Compare a flash light and a laser pointer aimed at a wall 10meters/30 feet away. We would see a small diameter dot from the laser and from the flash light, a very large diameter circle illuminating the wall.

How laser-like could you make a microwave or millimetre-wave in the sense that it would only hit a very small area, concentrated into a small dot on the sensor or whatever device the measuring uses.

I've heard the word "maser" but I don't know if that has any relevance here.

I hope I gave sufficient description of what my question is. (-How small diameter can you make a EM "beam" OR -Is transmitting a "beam" of electromagnetism with a very small cross section area, like a laser, possible?)
« Last Edit: October 16, 2021, 01:27:59 pm by cape zoloh »
 

Offline HB9EVI

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #1 on: October 16, 2021, 02:51:47 pm »
first guess would be, that it depends from the aperture of the antenna; if we talk about 10-100GHz, the aperture on such frequencies is quite small already due to the used high gain antennas (horn antennas or parabolic dishes for example); in the practical world, as hamradio operator you have to align your GHz-setup quite accurately, within an angle of 2-3° or less to hit the beam of your counterpart
but after all, I don't see real ways to focus a GHz-beam in the manner you can do it in the spectrum of light with a laser.
 

Offline nfmax

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #2 on: October 16, 2021, 02:56:07 pm »
The only difference between ligyt and radio waves is wavelength. The physics of Gaussian Beams are the same: https://en.wikipedia.org/wiki/Gaussian_beam
 

Offline dmills

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #3 on: October 16, 2021, 02:57:29 pm »
Depends on the ratio of the beam aperture to the wavelength in question among other things.

This is why free space laser doings over significant distances (Like say hitting that reflector on the moon) generally start off with a reverse telescope because the beam starting out say a meter in diameter will diverge much less then one starting out 1mm in diameter all things being equal. 

Figure high microwave as a few mm wavelength, and visible light as a few hundred nm wavelength, so the aperture for the microwave emitter needs to be about 10,000 times the aperture of the optical emitter to obtain the same far field divergence.

End of the day they are both EM waves, so the same optical principles apply to both.
 

Offline richnormand

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #4 on: October 16, 2021, 03:00:33 pm »
This should answer your question:
https://physics.stackexchange.com/questions/70415/lasers-and-collimation

The wave nature of light, radio waves or sound waves are pretty similar in that respect for a single source.
With microwaves you can also use a phased array and have a larger virtual source aperture to play with.
« Last Edit: October 16, 2021, 03:03:26 pm by richnormand »
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Offline mzzj

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #5 on: October 17, 2021, 07:09:27 pm »

Figure high microwave as a few mm wavelength, and visible light as a few hundred nm wavelength, so the aperture for the microwave emitter needs to be about 10,000 times the aperture of the optical emitter to obtain the same far field divergence.

End of the day they are both EM waves, so the same optical principles apply to both.
easy, just get one of these https://en.wikipedia.org/wiki/Five-hundred-meter_Aperture_Spherical_Telescope
 

Offline antenna

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #6 on: October 17, 2021, 08:10:45 pm »
Make a big lens made of wax :)

Sir Lawrence Bragg from the Royal Institution of Great Britain shows how microwaves go through materials like wax and glass and uses a normal optical lens to focus microwave RF.

 

Offline radiolistener

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Re: Laser-like narrow cone of Mhz/Ghz waves?
« Reply #7 on: October 17, 2021, 10:47:46 pm »
How laser-like could you make a microwave or millimetre-wave in the sense that it would only hit a very small area, concentrated into a small dot on the sensor or whatever device the measuring uses.

You can focus radio wave with reflectors at some point, the same as flashlight or laser doing it. But lower frequency has longer wavelength, so the minimum focus point will limited with about wavelength.

So, if you're trying to focus 10 mm wave, the minimum focus point size will be about 10 mm.
Since laser which works in visible band has about 500-600 nm wavelength, you can focus it into 500-600 nm point.

but after all, I don't see real ways to focus a GHz-beam in the manner you can do it in the spectrum of light with a laser.

You can do it for GHz wave with plexiglass lens, for GHz range beam it works the same as it works for a light.

For example here is demonstration of 10 GHz wave reflection in the plexiglass prizm vs cube:


It also shows effect of near field zone which explain why you cannot focus wave at the point which size is less than 0.5-1 wavelength.

As you can see, if there is a gap between two prizm, with size less than a wavelength, the wave bypass through prizm. But when the gap size is more than 1-2 wavelength, the wave is fully reflected in the prizm.
« Last Edit: October 17, 2021, 11:37:52 pm by radiolistener »
 


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