A recent article in C4ISR Journal is complete in that it highlights both the pros and cons associated with the L-, Ku- and Ka frequency bands commonly used in satellite communications. The article includes the observation that Ka-band for the military market won’t be “supplanting Ku any time soon. The Ka geographic coverage will be too limited.”
I would, however, like to comment and elaborate on the statement “Ka signals are higher power and frequency than today’s widely-used L and Ku commercial bands, which means they can send more data to the small antennas required for aircraft applications.” In my opinion, the statement can be considered accurate only with the use of the qualifier “today’s widely-used” L and Ku commercial bands. While true, I think it would have helped readers to note that the Ku-band systems being manufactured today will eliminate this discrepancy.
This article provides an incomplete — and inaccurate — picture of how Ku-band is going to be used alongside the new Ka-band systems coming to market. The article doesn’t include the new Ku-band systems being manufactured today that reach small aircraft antennas, just as will be possible with the new Ka-band systems.
Ka-band satellites achieve their higher power by focusing available satellite power into a small area, commonly called a “spot beam.” This is a good, valid choice but, it is also a trade-off. In satellite design, one must choose between performance and coverage. Every satellite has a limit on how many spot beams it can support and, consequently, a limit on the aggregate geographic coverage. The better the performance, the smaller the individual beam — and the smaller the aggregate coverage.
This trade-off is one of the reasons behind the observation that Ka-band geographic coverage will be limited in some instances. Such a trade-off is exemplified by Inmarsat’s Global Express service which plans global coverage by using spot beams larger than EpicNG. This choice results in a total throughput for Global Express, per satellite, that is about one third that of an Intelsat EpicNG satellite. In addition, only 81% of the Global Express coverage can be in use at any one time (72 of the 89 beams).
Ku-band satellites, historically, had wider beams due to market needs for wide area broadcast and/or multicast coverage, meaning the market chose larger coverage over improved performance. But market needs evolve and Intelsat’s EpicNG-class of satellites will complement our existing wide geographic coverage with multi-spot, that is highly focused, higher power, Ku-band coverage. Ku-band performance on EpicNG-class satellites is on par with or exceeds performance on Ka-band, multi-spot satellites.
It is the size of the beam, not its transmission frequency, that determines performance. And for many customers, both throughput AND geographic coverage are essential to building efficient, global networks. For those customers, we are building EpicNG.
Click here for a white paper with additional information on high throughput Ku-band for aero applications.