A respected industry veteran recently asked me the following question: “Wouldn’t it be great if an external [aircraft] antenna didn’t distort the beauty of the smooth and streamlined fuselage to such a degree that it resembles a large Halloween wart, causes drag, increases fuel consumption and makes a great ‘ice catcher’ in the air?”
I responded by telling the gentleman that, in truth, I’ve personally come to love the sight of an antenna blister on an aircraft simply because of what it means for me as a businesswoman and an avid user of social media. That sounds a tad selfish, but I’m not alone! Road warriors increasingly expect to be connected in-flight. And they’ve got insatiable appetites (check out Aviation Week journalist Rupa Haria’s blog about the 400MB of data she used on Qatar Airways’ Boeing 787 inaugural flight).
Much is written about the antenna systems housed beneath radomes (be they current Ku antennas or forthcoming Ka antennas). After all, the antenna gets the job done, talks to the satellites and so on.
But what about the humble radome itself? It doesn’t seem to get a lot of attention, and yet, radomes will play a big role in shaping the inflight connectivity landscape moving forward. I came to appreciate this fact when I had the opportunity to speak with an executive from Saint-Gobain Performance Plastics during the recent Aircraft Interiors Expo, Americas in Seattle.
Saint-Gobain has been designing radomes since 1947, and, in the commercial space, is considered a significant player in the market. It is sole supplier to Row 44, “and would be sole on the Panasonic [Ku system], but they’re using some Connexion by Boeing radomes as well”, says Saint-Gobain sales manager Robert Bogue.
Saint-Gobain is also involved in developing Ka-band radomes, and is helping to write the specs that will define design and performance. “We’ve already designed a Ka [radome] for a special mission application. I can’t tell you for who, because it’s special mission, but it’s a tail radome for Ka-band and we’re in the process of developing fuselage versions of this.”
But the process hasn’t been a cake walk. “Most of our radomes, the Ku-band and L-band radomes, are all honeycomb core. A C-sandwich is the layer of laminates on the outside, with a core on the inside, and honeycomb is used widely because it gives transmissivity. The problem with Ka is that the wavelength actually bounces inside the honeycombs and distorts the frequency distribution, the transmissivity, so you can’t use a honeycomb core. But honeycomb is best for Ku. So a lot of people want us to design a Ku-Ka band [radome] combination, but it’s very difficult to do because it’s going to be a long radome with a section for Ka.”
According to Bogue, a Ka radome “costs more money than a radome we’ve made for Ku. The materials are more expensive. It involves more laminates. It’s a heavier radome, a bigger radome.”
He explains: “It has to do with the wavelength and getting the wavelength through the material. The idea would be to design optimally for Ku, if you had one radome concept, and then to tune up the Ka transmissivity problems with the ability of the wider bandwidth that you have there. So you’d have an optimal Ku-band radome, and a less than optimal Ka, but you can adjust the Ka in terms of how you amplify it and filter it.”
Instead of honeycomb, Ka radomes need a foam core, he says. “The small cells in the foam don’t disturb the wavelength like the big cores and honeycombs do.”
Qest, which supplies antenna apertures for the Tecom-made Ku-band antennas used by Row 44, agrees with Bogue on this point. “From our point of view we have to agree that the physics of Ku and Ka antenna radomes are significantly different starting with a key factor, which is thickness. Because usually thickness is related to the wavelength so, with Ka, you have double the frequency, which means half the wavelength so the radome should be half as thick as a Ku radome, but this causes problems with bird strike tests. Then, if your radome is thicker you lose signal quality,” says Qest director of sales and marketing Michael Stobinski.
He says Qest has also looked at dual Ku-Ka configurations “from an antenna perspective as well as from a radome perspective and I fully agree that that’s certainly feasible. This dual-frequency radome for Ku and Ka is technically difficult but not impossible.”
Some industry stakeholders would understandably prefer a paradigm whereby commercial airlines could change antennas, and their associated carriers/providers, just as fast and easily as we change cell phone providers (a sentiment expressed by the industry veteran first presented in this piece).
Saint-Gobain’s Bogue says he is hearing “from the guys who design systems, the technical guys, the qualify guys … that they’re looking for a whole system that – everything right up to the radome – is the same and that you can just pop the radome off”, change out a Ku-band antenna for a Ka-band antenna, and put the cap back on.
Row 44, for instance, recently told the APEX editor’s blog that its systems “are ready to take Ka and we’re excited for that day to come but we think it’s a little ways away”.
There is a theory, adds Bogue, “that you could make one radome that does both but whenever you do that you’re giving up something on each side. I think the best solution is the one I described, where you have a whole system that has a cap called a radome that you take off, and you change your antenna, and you put a new radome on that is compliant with that antenna.”
What’s clear is that the stakes are high for all players in the inflight connectivity space. “This is a horse race right now and we’re all trying to get their first. And it’s not just us radome guys who are in the horse race; it’s also the system designers for Ka. They have to decide what’s going to be the most economical system to sell,” says Bogue.
[Editor's note: Honeywell, which is developing Ka-band antennas and radomes for Inmarsat's Global Xpress service, doesn't agree with some of the above comments.“I can state categorically that Ka radomes will not be larger than Ku either for air transport or business aviation,” says John Broughton, director product management, Global Xpress satcom. We hope to hear more from Honeywell later this week.]