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Comment by ArkyBeagle | Hacker News Reader

80 GHz isn't quite optical yet. It's a couple octaves down from infrared. SFAIK, it's still very much radio.

a great deal lower, the optical ITU DWDM grid is around 191.7 THz to 196.1 THz

The more general dividing line between microwave and infrared ( outside comms ) is 300 GHz, which was what I meant.

That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band.

It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical conclusion and you have imagined a 9/125 fiber.

But it's something of an apparently completely different... phenotype from a small waveguide.

The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?

Apparently a block of plastics like Delrin works:

http://www.physics.rutgers.edu/ugrad/205/manuals/micro.pdf

The key part in physics is it's still a wave... And a singlemode fiber is a type of waveguide. A 120GHz signal is a wave, a 171 THz signal is a wave, the latter just has a much shorter wavelength.

300Ghz ends up with a wavelength of 1mm, so it more follows the pattern of bandwidth assignment, which likes nice round numbers given in wavelength.

Back in 60's AT&T make lots and lots of circular waveguide, intending to bury it across the country. One of the circular modes is dispersionless; then fiber was invented; lot's of money lost on circular waveguide.

Interesting that mmWavguide is still rectangular. Wonder if one could do a mmWave fiber? Don't see why not.

millimeter wave waveguide on the rear of a parabolic antenna (30, 60cm dish) is actually circular (cylindrical), supporting dual polarity operation (opposite H and V). Individual radio heads like this russian radio or other 80 GHz radios are still single polarity. In certain scenarios you can mount two radio heads on a T-shaped waveguide on the rear of one dish antenna, one in H, one in V.

Thanks for the info. I got to mess with W-band stuff years ago, but I'm mostly Ku and below now. Would love to tear down some 80 GHz hardware.

Have you seen anything come of the "angular momentum" polarization discovered a few years ago? Seemed specific for P2P microwave.

I've yet to see a product of any sort I can buy with a credit card or purchase order. Would also like to know if anything comes of it.

I would love to hear more about that - have any links? From a quick google, all I can dig up makes it sound like it's normal circular polarization, which is used quite often in satellite. Not sure why it wouldn't make it into terrestrial, since it has some interesting advantages (no x-pol alignment issues!)

Google "angular momentum antenna". IEEE had a write up a few years ago, but details still lacking. It was simple as twisting the dish surface into a helix, but they didn't say how many modes could be generated.

Is it a Russian company? I only found Estonian and Swedish contact details on their website. Both countries are very much not Russia.

Yes elva-1 is a Russian company, most likely they're trying to obfuscate that on their English language web presence. It is sort of a shame because they are just as competent as many of the California based microwave engineering firms, and have been around for 25+ years. Their roots are in military radar systems much like some of the Israeli RF companies (Ceragon, etc).

Sorry, I work in a photonics lab so in casual conversation more of the spectrum is "optical" to me. I just meant to ask if you just increase your sampling rate doesn't that mean you have to worry more about things like dispersion happening along the path of the signal?

Optical and microwave are sort of an arbitrary distinction, so you're also right :) There's even the "millimeter wave" designation, or E(xtremely)HF.

Different frequencies scatter differently. This isn't bad: https://transition.fcc.gov/Bureaus/Engineering_Technology/Do...

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