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26-500: Milstar Block I spacecraft, or Milstar Developmental Flight Satellite (DFS)-1 and -2, were designed with a Low Data Rate (LDR) payload in the +X wing of the satellite that broadcast in the Super High Frequency (SHF) and Extremely High Frequency (EHF) ranges, and also a classified communication payload in the -X wing. The DFS-1 satellite was launched on 7 February 1994 aboard the first Titan IV(401)A rocket, but with

52-423: A band , or by similar NATO or EU designations. Microwaves propagate solely by line of sight ; because of the small refraction due to their short wavelength, the groundwave and ionospheric reflection ( skywave or "skip" propagation) seen with lower frequency radio waves do not occur. Although in some cases they can penetrate building walls enough for useful reception, unobstructed rights of way cleared to

78-471: A quarter wave whip antenna for the SHF band is between 2.5 and 0.25 centimeters long. Omnidirectional antennas have been developed for applications like wireless devices and cellphones that are small enough to be enclosed inside the device's case. The main antenna used for these devices is the printed inverted F antenna (PIFA) consisting of a monopole antenna bent in an L shape, fabricated of copper foil on

104-415: A few degrees or less, and often must be aimed with the aid of a boresight . Another type of antenna practical at microwave frequencies is the phased array , consisting of many dipoles or patch antennas on a flat surface, each fed through a phase shifter , which allows the array's beam to be steered electronically. The short wavelength requires great mechanical rigidity in large antennas, to ensure that

130-529: A hybrid mix of largely Block I support systems and LDR payload and a MDR (Medium Data Rate) Block II payload) was launched on 30 April 1999, using a Titan IV(401)B rocket. Due to a database error affecting the attitude control system of the Centaur upper stage of its carrier rocket, it was placed into a lower orbit than had been planned, and damaged by deployment at excessive rates. It could not be raised into its operational orbit due to fuel limitations. Its orbit

156-423: Is a range of frequencies contained in the microwave region of the electromagnetic spectrum . Common usage places this range between 33 and 50  GHz , but may vary depending on the source using the term. The foregoing range corresponds to the recommended frequency band of operation of WR22 waveguides. These frequencies are equivalent to wavelengths between 6 mm and 9.1 mm in air/vacuum. The Q band

182-588: Is in the EHF range of the radio spectrum . The term "Q band" does not have a consistently precise usage in the technical literature, but tends to be a concurrent subset of both the IEEE designated K a band (26.5–40 GHz) and V band (40–75 GHz). Neither the IEEE nor the ITU-R recognize the Q band in their standards, which define the nomenclature of bands in the electromagnetic spectrum. The ISO recognizes

208-667: Is the ITU designation for radio frequencies (RF) in the range between 3 and 30  gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes and horn antennas , so they are used for point-to-point communication and data links and for radar . This frequency range

234-491: Is used for most radar transmitters, wireless LANs , satellite communication , microwave radio relay links, satellite phones ( S band ), and numerous short range terrestrial data links. They are also used for heating in industrial microwave heating , medical diathermy , microwave hyperthermy to treat cancer, and to cook food in microwave ovens . Frequencies in the SHF range are often referred to by their IEEE radar band designations: S , C , X , K u , K , or K

260-645: The 148th Space Operations Squadron at Vandenberg SFB are responsible for providing real-time satellite control and communications payload management. In August 2010 control of the Milstar system was transferred to the Advanced Extremely High Frequency program, in preparation for the launch of the first AEHF satellite, USA-214 . Advanced Extremely High Frequency satellites are intended to replace Milstar. Milstar satellites provide secure, jam resistant, worldwide communications to meet

286-589: The Cape Canaveral Air Force Station . The satellites are designed to provide communications which are hard to detect and intercept, and to be survivable in the event of nuclear warfare . The spacecraft have a mass of 4,500 kilograms (9,900 lb), and are equipped with solar panels which generate eight kilowatts of electric power to power its transponders . Both Block I and Block II satellites provide low data-rate communications at bandwidths between 75 bit/s and 2,400 bit/s, whilst

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312-593: The printed circuit board inside the device. Small sleeve dipoles or quarter-wave monopoles are also used. The patch antenna is another common type, often integrated into the skin of aircraft. The wavelengths are also small enough that SHF waves can be focused into narrow beams by high gain directional antennas from a half meter to five meters in diameter. Directive antennas at SHF frequencies are mostly aperture antennas , such as parabolic antennas (the most common type), lens , slot and horn antennas . Large parabolic antennas can produce very narrow beams of

338-422: The tropopause some of the microwaves are scattered back to Earth to a receiver beyond the horizon. Distances of 300 km can be achieved. These are mainly used for military communication. The wavelength of SHF waves is short enough that efficient transmitting antennas are small enough to be conveniently mounted on handheld devices, so these frequencies are widely used for wireless applications. For example

364-470: The Block II spacecraft can also provide medium data-rate communications between 4.8 kbit/s and 1.544 Mbit/s. The satellites' uplinks operate in the Q band , while their downlinks operate within the K band . The uplink corresponds to the extremely high frequency band while downlink corresponds to the super high frequency radio band. Super High Frequency Super high frequency ( SHF )

390-506: The Q band; however, the range therefore defined is 36 to 46 GHz. Other ISO frequency band definitions do not precisely match the concurrent definitions of the IEEE and ITU-R. The Q band is mainly used for satellite communications, terrestrial microwave communications and for radio astronomy studies such as the QUIET telescope . It is also used in automotive radar and in radar investigating

416-411: The atmosphere increase with frequency, limiting the use of high SHF frequencies for long range applications. Small amounts of microwave energy are randomly scattered by water vapor molecules in the troposphere . This is used in troposcatter communications systems, operating at a few GHz, to communicate beyond the horizon. A powerful microwave beam is aimed just above the horizon; as it passes through

442-633: The classified -X wing payload deactivated. It was followed by the DFS-2 spacecraft on 7 November 1995. DFS-2 was similar to DFS-1, but the classified payload was replaced by ballast in the form of a precision machined aluminum block to maintain the weight and balance characteristics of the satellite. Both Block I satellites (USA-99 and USA-115) are still operational as of August 2016, over 20 years since they were launched. The four later satellites were Block II spacecraft, which featured an additional medium data-rate payload. The first Block II satellite (DFS-3m,

468-534: The first Fresnel zone are usually required. Wavelengths are small enough at microwave frequencies that the antenna can be much larger than a wavelength, allowing highly directional (high gain ) antennas to be built which can produce narrow beams. Therefore, they are used in point-to-point terrestrial communications links, limited by the visual horizon to 30–40 miles (48–64 km). Such high gain antennas allow frequency reuse by nearby transmitters. They are also used for communication with spacecraft since

494-805: The first time allow significant signal processing to be done at these frequencies. Sources of EHF energy are much more limited and in an earlier state of development. ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m UHF 300 MHz/1 m 3 GHz/100 mm SHF 3 GHz/100 mm 30 GHz/10 mm EHF 30 GHz/10 mm 300 GHz/1 mm THF 300 GHz/1 mm 3 THz/0.1 mm Q band The Q band

520-515: The other hand, they are the highest frequencies which can be used for long distance terrestrial communication; higher frequencies in the EHF (millimeter wave) band are highly absorbed by the atmosphere, limiting practical propagation distances to one kilometer or less. The high frequency gives microwave communication links a very large information-carrying capacity ( bandwidth ). In recent decades many new solid state sources of microwave energy have been developed, and microwave integrated circuits for

546-495: The output stage of the transmitter or the RF front end of the receiver is located at the antenna. SHF frequencies occupy a "sweet spot" in the radio spectrum which is currently being exploited by many new radio services. They are the lowest frequency band where radio waves can be directed in narrow beams by conveniently sized antennas so they do not interfere with nearby transmitters on the same frequency, allowing frequency reuse. On

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572-487: The radio waves arrive at the feed point in phase. At microwave frequencies, the types of cable ( transmission line ) used to conduct lower frequency radio waves, such as coaxial cable , have high power losses. Therefore, to transport microwaves between the transmitter or receiver and the antenna with low losses, a special type of metal pipe called waveguide must be used. Because of the high cost and maintenance requirements of long waveguide runs, in many microwave antennas

598-547: The requirements of the United States military. They were built by Lockheed Martin Missiles and Space Corporation , at a cost of US$ 800 million each. Each satellite has a design life of 10 years. Six were built, of which five reached their operational geosynchronous orbits , and remain in service. Launches were made using Titan IV rockets with Centaur upper stages, and all six occurred from Space Launch Complex 40 at

624-572: The satellites. The Military Satellite Communications Systems Wing (MCSW) division of the Space and Missile Systems Center , located at Los Angeles AFB was responsible for development and acquisition of the Milstar space and mission control segments. The Electronic Systems Center at Hanscom AFB is responsible for the US Air Force portion of the terminal segment development and acquisition. The 4th Space Operations Squadron at Schriever SFB and

650-471: The waves are not refracted (bent) when passing through the ionosphere like lower frequencies. The wavelength of SHF waves creates strong reflections from metal objects the size of automobiles, aircraft, and ships, and other vehicles. This and the narrow beamwidths possible with high gain antennas and the low atmospheric attenuation as compared with higher frequencies make SHF the main frequencies used in radar . Attenuation and scattering by moisture in

676-478: Was raised as much as possible to increase the expected lifetime and then it was permanently turned off after 10 days. It was the third consecutive, and last, failure of a Titan IV rocket. The remaining three satellites (DFS-4, -5, and -6) were launched on 27 February 2001, 15 January 2002, and 8 April 2003. The Milstar system consists of three segments; the space segment which consists of the six satellites, ground terminals and users, and stations to command and control

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