The C-band is a range of microwave radio frequencies in the region of 4–8 GHz commonly used both by communications satellites and terrestrial microwave radio communications. Downlink frequencies are 3.7–4.2 GHz and uplink frequencies are 5.925–6.425 GHz.
The C-band was the first band to be used for satellite communications. However, because it is also used for carrying terrestrial signals, it quickly became overloaded. When this happened, some satellites began to be equipped to handle Ku-band communications.