The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4 gigahertz (GHz). Thus it crosses the conventional boundary between the UHF and SHF bands at 3.0 GHz. The S band is used by airport surveillance radar for air traffic control, weather radar, surface ship radar, and some communications satellites, especially those used by NASA to communicate with the Space Shuttle and the International Space Station. The 10 cm radar short-band ranges roughly from 1.55 to 5.2 GHz. The S band also contains the 2.4–2.483 GHz ISM band, widely used for low power unlicensed microwave devices such as cordless phones, wireless headphones (Bluetooth), wireless networking (WiFi), garage door openers, keyless vehicle locks, baby monitors as well as for medical diathermy machines and microwave ovens (typically at 2.495 GHz). India's regional satellite navigation network (IRNSS) broadcasts on 2.483778 to 2.500278 GHz.
In the U.S., the FCC approved satellite-based Digital Audio Radio Service (DARS) broadcasting in the S band from 2.31 to 2.36 GHz, currently used by Sirius XM Radio. More recently, it has approved for portions of the S band between 2.0 and 2.2 GHz the creation of Mobile Satellite Service (MSS) networks in connection with Ancillary Terrestrial Components (ATC). There are presently a number of companies attempting to deploy such networks, including ICO Satellite Management and TerreStar.
The 2.6 GHz range is used for China Multimedia Mobile Broadcasting, a satellite radio and mobile TV standard which, as with proprietary systems in the U.S., is incompatible with the open standards used in the rest of the world.
In May 2009, Inmarsat and Solaris Mobile (a joint venture between Eutelsat and SES, now EchoStar Mobile) were awarded each a 2×15 MHz portion of the S band by the European Commission. The two companies are allowed two years to start providing pan-European MSS services for 18 years. Allocated frequencies are 1.98 to 2.01 GHz for Earth to space communications, and from 2.17 to 2.2 GHz for space to Earth communications. Eutelsat W2A satellite launched in April, 2009 and located at 10° East is currently the unique satellite in Europe operating on S band frequencies.
In some countries, S band is used for Direct-to-Home satellite television (unlike similar services in most countries, which use Ku band). The frequency typically allocated for this service is 2.5 to 2.7 GHz (LOF 1.570 GHz).
IndoStar-1 was the world's first commercial communications satellite to use S-band frequencies for broadcast (pioneered by van der Heyden), which efficiently penetrate the atmosphere and provide high-quality transmissions to small-diameter 80 cm antennas in regions that experience heavy rainfall such as Indonesia. Similar performance is not economically feasible with comparable Ku- or C-band DTH satellite systems since more power is required in these bands to penetrate the moist atmosphere.
Wireless network equipment compatible with IEEE 802.11b and 802.11g standards use the 2.4 GHz section of the S band. Some digital cordless telephones operate in this band too. Microwave ovens operate at 2495 or 2450 MHz. IEEE 802.16a and 802.16e standards use a part of the frequency range of S band; under WiMAX standards most vendors are now manufacturing equipment in the range of 3.5 GHz. The exact frequency range allocated for this type of use varies between countries.
In North America, 2.4–2.483 GHz is an ISM band used for unlicensed spectrum devices such as cordless phones, wireless headphones, and video senders, among other consumer electronics uses, including Bluetooth which operates between 2.402 GHz and 2.480 GHz.
Airport surveillance radars typically operate in the 2700–2900 MHz range.
Particle accelerators may be powered by S-band RF sources. The frequencies are then standardized at 2.998 GHz (Europe) or 2.856 GHz (US).
In the United States, the 3.55 to 3.7 GHz band is becoming shared spectrum under rules adopted by the Federal Communications Commission in April 2015 as a result of the National Broadband Plan (United States). The biggest user of CBRS (Citizens Broadband Radio service) spectrum is the United States Navy. Cable companies are planning to use the band for wireless broadband in rural areas, with Charter Communications beginning tests of the service in January 2018.
Used as a transmit intermediate frequency in satellite communications as a replacement for L band where a single/shared coaxial connection is used between the modem/IDU and antenna/ODU for both the transmit and receive signals. This is to prevent interference between the transmit and receive signals which would otherwise not occur on a dual coaxial setup where the transmit and receive signals are separate and both can use the whole L-band frequency range. In a single coaxial connection using S-Band to "frequency shift" the transmit signal away from L band, a multiplier such as 10, is usually applied to form the SHF frequency. For example, the modem would transmit at 2.815 GHz IF (S Band) to the ODU and then the ODU up-converts this signal to 28.15 GHz SHF (Ka Band) towards the satellite.  
Optical communications S band