Inflight connectivity: what next after Ka-band frequencies?

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An Inmarsat I-5 satellite for its Ka-band GX Aviation service.
An Inmarsat I-5 satellite for its Ka-band GX Aviation service.

There has always been a war of words between Ku- and Ka-band operators, with both claiming their service is better. But what about the future? Is there an alternative on the horizon?

Ku and Ka are not the only fruit. There are microwave frequencies available that are even higher, such as the Q (33 to 50 GHz) and V (40–75 GHz) bands.

But first a quick recap.

The “band” in use refers to the radio frequencies used to and from the satellite:

  • L-band uses frequencies in the 1 to 2GHz range
  • Ku-band utilises approximately 12-18GHz, and
  • Ka-band services use the 26.5-40GHz segment of the electromagnetic spectrum.


And in case you were wondering “Ku” stands for “Kurz unten” – German for the band just underneath the “short” or K-band. Not surprisingly “Ka” stands for “Kurz above”.

So what you cry? Generally, the higher the frequency the more bandwidth you can squeeze out of the system. The difference is just like an FM radio broadcast being compared with medium wave. The higher frequency VHF radio (100MHz) band gives you greater bandwidth than medium wave (1MHz) and the sound quality is better.

Scale this up to the satellite’s microwave frequencies and Ka-band should give you more digital bandwidth than Ku, which in turn should give greater bandwidth than L-band.

You can read more about this in our feature.

The arguments start when you use high power spot beams that can “boost” the data throughput – hence operators argue that Ku-band HTS satellites may outperform Ka-band ones. We’ll leave that argument for now!

But if going higher in frequency could enable more throughput is Ka-band the limit? Well, yes and no.

The V and Q bands are above Ka, and potentially offer even higher data throughputs.

The Q band is a range of frequencies contained in the microwave region of the electromagnetic spectrum. Common usage places this range between 33 to 50 GHz, equivalent to wavelengths between 9 mm and 6 mm.

The V band runs from 50 to 75 GHz, equivalent to wavelengths between 7.5mm and 4mm.

Catch 22

Kymeta's Bill Marks and the mTenna.
Kymeta’s Bill Marks and the mTenna.

So why don’t we just move to these higher bands? The first problem is that the antenna and terminal technology has not been available, but that is slowly changing. A Kymeta engineer told me at the recent Abu Dhabi Space Congress that its new flat-panel mTenna could be made to work at these higher frequencies, but it is Catch 22.

There are no commercial satellites that use V and Q bands, so there is no development work on terminals. Likewise, there is no development work on the satellites as there is no demand.

The even bigger issue is rain fade. Rain fade occurs when moisture or water droplets in the air attenuate radio signals and generally gets worse as you go higher in frequency.

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This isn’t such generally a problem with an aircraft flying at 35,000 feet, but it is a problem with increasing gate-to-gate connectivity, where clouds and rain could destroy the signal to the aircraft on the ground or at lower altitudes.

Rain fade

It can also be a problem in the tropics where the high attenuation experienced is caused by significantly higher rainfall rates compared to other parts of the world and even the air is moist.

As the operating frequency is increased, the attenuation and scintillation effects of atmospheric gas and clouds also become more severe.

The good news is that there are some “sweet spots” in the microwave electromagnetic spectrum where atmospheric attenuation is less than in other parts.

FMT (Fade Mitigation Techniques) are available to overcome real time atmospheric attenuation, such as increasing power, using multiple satellite links and more resistant waveforms.

The V band has been used for satellite communication. On December 15 1995 60 GHz was used by the world’s first cross-link communication between satellites in a constellation. This communication was between the U.S. Milstar 1 and Milstar 2 military satellites. The frequency is attractive for secure satellite crosslinks because it allows for high data rates and narrow beams.

The other good news is that antennas for these higher frequencies could be much smaller than Ku- and Ka-band ones. But the bad news is that more heat will need to be dissipated as we go up in frequency?

So will we ever see Q- and V-band inflight connectivity?

It is hard to say no as data rate requirements are likely to keep growing. Remember when we thought 2400bps modems and 128k of RAM were enough?

But high-throughput Ku/Ka satellites (HTS), higher power spots beams and constellations of low-earth orbiting satellites mean we may have no need for higher frequency satellites.

And we can’t change the laws of physics in terms of rain fade.

Only time will tell.

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