Ku-band
The Ku-band is a frequency range of roughly 12 to 18 gigahertz in which satellites send and receive radio signals to and from Earth. It is the range over which classic satellite television and a large portion of satellite internet run.
Radio signals are waves, and waves are distinguished by how fast they oscillate. This number of oscillations is called frequency and is measured in hertz. The Ku-band is a specific section on this scale: roughly 12 to 18 billion oscillations per second, i.e. 12 to 18 gigahertz. Decades ago, engineers named such sections with letters so that they wouldn’t constantly have to cite numbers. The “u” in Ku stands for “under,” because this range lies directly below the older K-band. Anyone who sees a satellite dish on a balcony is almost always looking at an antenna for the Ku-band.
The range in which satellite television grew up
Frequencies are a scarce resource. Each range can only be assigned once, otherwise users would interfere with one another. Authorities therefore divide up the scale worldwide and assign individual sections to specific purposes. The Ku-band was reserved early on for satellite broadcasting, and this head start still has an effect today.
The practical advantage lies in antenna size. The higher the frequency, the shorter the wave, and the smaller the dish is allowed to be. In the lower C-band, antennas several meters in diameter are needed. In the Ku-band, 60 to 80 centimeters are often enough. Only this made satellite television affordable for ordinary households.
Economically, the band is therefore fiercely contested. Classic television satellites have occupied it for decades, and new internet networks are pushing in. Whoever holds a frequency license for a region holds a real asset. News about satellite operators is often precisely about such rights.
Why rain weakens the signal
A satellite in geostationary orbit sits about 36,000 kilometers above the equator and appears to stand still from the ground. It receives a signal from a ground station, amplifies it, and sends it back on a different frequency. The uplink and the downlink use different frequencies so that the two don’t overlap. In the Ku-band, the downlink to Earth lies roughly around 12 gigahertz, the uplink at about 14 gigahertz.
The dish on the house is a mirror. It focuses the very weak incoming waves onto a single point, where the receiving head sits. That’s why it must be precisely aligned. Just a few degrees of deviation are enough to lose the picture.
The weakness of the Ku-band is water. Raindrops are roughly on the same order of magnitude as these short waves and absorb part of the energy. During a heavy thunderstorm, the picture sometimes drops out because of this, an effect engineers call rain fade. A common misconception is that the dish must be broken. Usually the cloud simply moves on.
From television reception to internet on airplanes
The Ku-band is most visible on rooftops. Reception of Astra or Eutelsat in Europe runs over this band. Outside broadcast vans at football matches also frequently send their footage back to the broadcaster over it.
It is also very important for connections on the move. Ships, aircraft, and military vehicles use Ku-band antennas because these are small enough to be carried along. Part of Starlink’s satellites also transmit in the Ku-band to customer terminals on the ground.
In the news, the term usually comes up in comparison with the Ka-band, which lies even higher and carries more data but reacts more sensitively to rain. Operators thus choose between speed and reliability. When a company announces it is building capacity in the Ka-band, this is precisely the trade-off at stake.