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IEEE 802.11 aka WiFi uses multiple ISM bands to transmit data,2.4,5 and 60 Ghz.The 24 GHz was never used in WiFi,why? Why did they jump from 5 to 60 and ignored 24? Why no wireless standard use this band?

I only saw this 24 band being used for car radar in older models,new cars use 77 GHz.The 24 GHz have big bandwidth and its worldwide avaliable ISM band,it seems perfect for some kind of short range domestic wireless aplication,it seems strange than nobody is using it.

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    \$\begingroup\$ Lots of people use the 24 GHz band. Satellite uplinks and radio navigation, mainly. \$\endgroup\$ – Finbarr Jul 18 '18 at 17:52
  • \$\begingroup\$ Didnt know that,thank you.Still,no domestic wireless standard use this band,I think it would be great for Bluetooth \$\endgroup\$ – wav scientist Jul 18 '18 at 18:25
  • \$\begingroup\$ @wavscientist would it? how so? Bluetooth is among the standards that suffers the least from contention in the 2.4 GHz band, and you simply get 20 dB more power over the same distance using the same directivity in 2.4 GHz than 24 GHz. \$\endgroup\$ – Marcus Müller Jul 18 '18 at 18:29
  • \$\begingroup\$ 24 GHz is inherently short range,also needs far smaller antena and while I agree Bluetooth suffers less in the overcrowded 2.4 band,its still overcrowded and its still problem even for Bluetooth.Furthermore,the 24 GHz band is used alot less and together with its short range due to poor penetration its almost interference free.While its expensive,its less so than 60 GHz and have better penetration.I read study where 60 GHz was blocked merely by large number of people standing in same room as the transmiter,24 GHz should not have this problem. \$\endgroup\$ – wav scientist Jul 18 '18 at 18:43
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    \$\begingroup\$ @wavscientist sadly, you're totally wrong! 24 GHz (23.something GHz to be exact) has a local maximum of atmospheric absorption over frequency – thanks to it exciting water vapor. So: 24 GHz isn't really great for watery and steamy situations. \$\endgroup\$ – Marcus Müller Jul 18 '18 at 18:55
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24 GHz and 60 GHz are significantly more expensive to deal with – whilst your average FR4 PCB is totally sufficient in material \$\epsilon\$ uniformity and \$\tan\delta\$, it won't do > 20 GHz.

Reliable connectors become very expensive.

Also, you either get much more loss per distance, or you use the reduced wavelength to build an antenna with larger directivity that's the same size than its 2.4 GHz counterpart. That makes sense for radar, but for communications, you don't want that (unless you can build even more complicated digital beamforming systems – a questions of cost and complexity).

New wireless broadband communication systems going to 60 GHz is a deliberate choice to go for the quasioptical channel, that solves a couple of the issues of the less selective / specular 2.4 GHz indoor channel out of necessity. You simply can't do future bandwidths in 2.4 GHz. If we could, we would. By going higher, we get drastically increased free-space loss and much narrower fading "holes", but we get the ability to do massive MIMO in indoors scenarios and get Gigahertzes of bandwidth. 24 GHz has a meagre 250 MHz of bandwidth – not that much more than 5 GHz already offers.

24 GHz is simply a bad tradeoff between much more cost and complexity vs advantages; you don't get the quasi-optical diversity, but you get all the mmWave complications.

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