The C band is a name given to certain portions of the electromagnetic spectrum, including wavelengths of microwaves that are used for long-distance radio telecommunications. The IEEE C-band (4 GHz to 8 GHz) - and its slight variations - contains frequency ranges that are used for many satellite communications transmissions, some Wi-Fi devices, some cordless telephones, and some weather radar systems. For satellite communications, the microwave frequencies of the C-band perform better under adverse weather conditions in comparison with Ku band (11.2 GHz to 14.5 GHz) microwave frequencies, which are used by other communication satellites. The adverse weather conditions, collectively referred to as rain fade, all have to do with moisture in the air, including rain and snow.
The NATO C-band
The IEEE C-band
The IEEE C-band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 4.0 to 8.0 gigahertz (GHz); however, this definition is the one followed by radar manufacturers and users, not necessarily by microwave radio telecommunications users.
The communications C-band was the first frequency band that was allocated for commercial telecommunications via satellites. The same frequencies were already in use for terrestrial microwave radio relay chains. Nearly all C-band communication satellites use the band of frequencies from 3.7 to 4.2 GHz for their downlinks, and the band of frequencies from 5.925 GHz to 6.425 GHz for their uplinks. Note that by using the band from 3.7 to 4.0 GHz, this C-band overlaps somewhat into the IEEE S-band for radars.
The C-band communication satellites typically have 24 radio transponders spaced 20 MHz apart, but with the adjacent transponders on opposite polarizations.  Hence, the transponders on the same polarization are always 40 MHz apart. Of this 40 MHz, each transponder utilizes about 36 MHz. (The unused 4.0 MHz between the pairs of transponders acts as "guard bands" for the likely case of imperfections in the microwave electronics.)
The C-band is primarily used for open satellite communications, whether for full-time satellite TV networks or raw satellite feeds, although subscription programming also exists. This use contrasts with direct broadcast satellite, which is a completely closed system used to deliver subscription programming to small satellite dishes that are connected with proprietary receiving equipment.
The satellite communications portion of the C-band is highly associated with television receive-only satellite reception systems, commonly called "big dish" systems, since small receiving antennas are not optimal for C-band systems. Typical antenna sizes on C-band capable systems ranges from 7.5 to 12 feet (2.5 to 3.5 meters) on consumer satellite dishes, although larger ones also can be used.
The C-band frequencies of 5.4 GHz band [5.15 to 5.35 GHz, or 5.47 to 5.725 GHz, or 5.725 to 5.875 GHz, depending on the region of the world] is used for IEEE 802.11a Wi-Fi and cordless telephone applications, leading to occasional interference with some weather radars that are also allocated to the C-band.
Slight variations in the assignments of C-band frequencies have been approved for use in various parts of the world, depending on their locations in the three International Telecommunications Union radio regions. Note that one region includes all of the Americas; a second includes all of Europe and Africa, plus all of Russia, and the third region includes all of Asia outside of Russia, plus Australia and New Zealand. This latter region is the most populous one, since it includes the People's Republic of China, India, Pakistan, Japan, and Southeast Asia.
|C-Band Variations Around The World|
|INSAT / Super-Extended C-Band||6.725–7.025||4.500–4.800|
The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range 5.650 to 5.925 GHz, and amateur satellite operations are allowed in the ranges 5.830 to 5.850 GHz for down-links and 5.650 to 5.670 GHz for up-links. This is known as the 5-centimeter band by amateurs and the C-band by AMSAT.
Other microwave bands
The microwave spectrum is usually defined as the electromagnetic spectrum that ranges from 1.0 GHz to 30 GHz in frequency, but some antiquated usages includes lower frequencies. Most common applications are within the 1.0 to 30 GHz range. Microwave frequency bands, as defined by the Radio Society of Great Britain (RSGB), are shown in the table below. Note that frequencies above 30 GHz are typically said to be in the "millimeter wave". because their wavelengths can be conveniently measured in millimeters (mm). The frequency of 30 GHz corresponds quite closely to a wavelength of 10 mm, or 1.0 centimeter.
|L band||1 to 2 GHz|
|S band||2 to 4 GHz|
|C band||4 to 8 GHz|
|X band||8 to 12 GHz|
|Ku band||12 to 18 GHz|
|K band||18 to 26.5 GHz|
|Ka band||26.5 to 40 GHz|
|Q band||30 to 50 GHz|
|U band||40 to 60 GHz|
|V band||50 to 75 GHz|
|E band||60 to 90 GHz|
|W band||75 to 110 GHz|
|F band||90 to 140 GHz|
|D band||110 to 170 GHz|
Footnote: "P-band" is sometimes incorrectly used for the Ku-band. "P" for "previous" was a radar band used in the United Kingdom that ranged from 250 to 500 MHz, which is now completely obsolete by the IEEE Standard 521, see  and . For other definitions see Letter Designations of Microwave Bands
Fiber optic communications
- The VSAT Installation Manual Video Presentation shows examples of the arrangement of the Feed for c-band polarization requirements
- VSAT Installation Manual with explanation of c-band polarization requirements for a VSAT