Ku-band

To alleviate congestion in C-band, many modern satellite communications systems operate in higher-frequency bands such as Ku-band. Satellites may carry a mix of C-band and Ku-band transponders, with the proportion selected according to coverage region and service requirements. Ku-band lies within the SHF range and offers increased capacity relative to C-band.

The ITU has allocated several portions of Ku-band to different satellite services and regions. In ITU Region 2 (the Americas), the 14/12-GHz band (14.00–14.50 GHz uplink and 11.70–12.20 GHz downlink) is allocated to the fixed-satellite service (FSS) and is not shared with terrestrial systems. In Regions 1 and 3, the 14/11-GHz band (14.00–14.50 GHz uplink and 10.95–11.70 GHz downlink) is allocated to FSS but requires coordination on the downlink because of sharing with terrestrial services. A third Ku-band allocation, commonly referred to as 18/12 GHz, is assigned to the BSS for direct-to-home television and related applications and is generally not shared with terrestrial systems.

Ku-band enables higher satellite transmit powers and smaller user antennas than C-band, particularly for BSS applications, where typical traveling-wave tube amplifier powers are on the order of 60–120 W compared with roughly 20–40 W in C-band systems. To limit adjacent-satellite interference, Ku-band BSS satellites are typically spaced about 6–9° apart in geostationary orbit, compared with approximately 2° spacing for Ku-band FSS satellites.

The principal disadvantage of Ku-band is its increased susceptibility to atmospheric attenuation, especially rain fade. Required fade margins depend on frequency, elevation, and climate, but are typically of the order of 6–10 dB, compared with about 2 dB for C-band systems. Although higher satellite EIRP can compensate for these losses, the greater sensitivity to rain can limit the suitability of Ku-band systems in tropical and high-rainfall regions.