2013

Wi-Fi on Aircraft with SPINNER Rotary Joints

High-speed internet connections or cellular networks aren’t readily available everywhere. When it’s essential to transmit large data volumes, the preferred (or often only) viable approach is to take advantage of satellite communications systems.

But how does Wi-Fi work on board airplanes?

More and more airlines now offer in-flight Wi-Fi. The required technology is either installed while building the aircraft or else retrofitted. It’s easy to tell which planes are equipped with Wi-Fi: the transmitter can be spotted on top of the fuselage directly behind the lateral rudders. It sends all data and other signals to a satellite in orbit around the earth, which relays them to the recipients.

In many cases, so-called VSAT (“very small aperture terminal”) systems operating in the Ku and Ka bands are used. These systems, which are installed on all kinds of vehicles or can even be worn, require very precise positioning of tight-beam antennas on the satellites. This is accomplished with rotary joints, which ensure accurate transmission of signals exchanged between a stationary transmitter and a movable antenna system while minimizing losses, independently of the angle of rotation.

The technical requirements for rotary joints can vary considerably from project to project, and also depend on the frequency band (Ku to Ka).

Applications in which both transmitted and received signals need to pass through the same waveguide call for rotary joints that support a fairly wide range of frequencies, with the downlink band extending from 10.75 to 12.75 GHz and the uplink band from 13.75 to 14.50 GHz. SPINNER supplies waveguide rotary joints of this kind in the R120/WR75 waveguide size and a variety of shapes.

For some projects, planners may want to dispense with a large band while still insisting on reliable signal transmission. Responding to these customer needs, SPINNER developed two single-channel, L-shaped R120/WR75 rotary joints. The standard model features IP40 ingress protection, and there is also a model equipped with an extra seal for IP 65 ingress protection that makes it suitable for outdoor use.

The rotary joints supplied for Wi-Fi applications are contactless versions with an extremely long life expectancy that is limited almost exclusively by wear of the roller bearings. The elimination of nearly all internal points of contact achieves a very low typical insertion loss of less than 0.1 dB and excellent cooling of the joint system. Both are essential prerequisites for enhanced robustness, which is required since these joints are subject to enormous temperature fluctuations due to changes in altitude, among other things.

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