L-band and S-band

The L-band and S-band occupy the frequency range from approximately 1 to 4 GHz and are sometimes collectively (and loosely) referred to as UHF in satellite communications contexts. These bands are useful for satellite communications because propagation is essentially line-of-sight, atmospheric absorption is relatively low, and man-made noise levels are modest. However, ionospheric effects such as scintillation and polarization rotation must be considered, particularly at low elevations and in equatorial and polar regions. While the available bandwidth is limited compared with C- and Ku-band systems, L- and S-band links are well suited to robust, highly available services.

The relatively long wavelengths permit the use of simple, low-cost antennas such as Yagi and helical antennas and enable compact, power-efficient user terminals. These characteristics make L and S band attractive for mobile and personal satellite communications, despite their lower achievable data rates.

L- and S-band spectrum is shared extensively with terrestrial services and other space services, including aeronautical and maritime systems, studio-to-transmitter links, radio astronomy, and deep-space communications. As a result, these bands are poorly suited to high-capacity geostationary satellite operation, both because of limited available bandwidth and the difficulty of coordinating spectrum use over very large geographic areas.

Historically, L band was first used extensively for mobile satellite services by MARISAT for ship-to-shore communications, alongside UHF payloads for US Navy use. Today, L and S band are allocated predominantly to the mobile-satellite service (MSS), particularly for satellite personal communications. For example, Globalstar uses L-band frequencies (around 1.6 GHz) for satellite-to-mobile links and S-band frequencies (around 2.5 GHz) for mobile-to-satellite links, while Iridium operates exclusively in L-band for user communications.