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8/3/2019 The FAA Global Navigation Satellite System
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The FAA Global Navigation Satellite System (GNSS) Program Office providessatellite (GPS) based positioning, navigation, and timing (PNT) services in theUnited States to enable performance-based (RNP/RNAV) operations for all phases
of flight from en route, terminal, approach, and surface navigation. PNT services arean essential enabler required to overcome the deficiencies in today's air trafficinfrastructure and support implementation of the Next Generation Air Transportation(NEXTGEN) system for the United States' National Airspace System (NAS). TheFAA's plan to provide PNT services requires implementation of two GPSaugmentation systems, the Wide Area Augmentation System (WAAS) and theGround Based Augmentation System (GBAS). Both systems improve the accuracy,availability, and integrity needed to support continuous all-weather use of GPS as aprimary means of navigation and automated dependent surveillance (ADS-B) within
the NAS.
The GNSS Team, along with other FAA organizations and numerous governmentaland non-governmental agencies, are all supporting a smooth transition to satellitenavigation. Visit us and see what’s new.
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Israeli military radar is typical of the type of radar used for air traffic control. The antenna
rotates at a steady rate, sweeping the local airspace with a narrow vertical fan-shaped
beam, to detect aircraft at all altitudes.
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or
speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather
formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaveswhich bounce
off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is
usually located at the same site as the transmitter.
Radar was developed in secret in nations across the world during World War II. The term RADAR was coined
in 1940 by the United States Navy as an acronymfor ra dio d etection a nd r anging .[1][2] The term radar has since
entered Englishand other languages as the common noun radar , losing all capitalization.
The modern uses of radar are highly diverse, including air traffic control, radar astronomy, air-defense
systems, antimissile systems; marine radars to locate landmarks and other ships; aircraft anticollision
systems; ocean surveillancesystems, outer space surveillance
and rendezvous systems; meteorologicalprecipitation monitoring; altimetry and flight control systems; guided
missiletarget locating systems; and ground-penetrating radar for geological observations. High tech radar
systems are associated with digital signal processing and are capable of extracting objects from very high
noise levels.
Other systems similar to radar have been used in other parts of theelectromagnetic spectrum. One example is
"lidar", which uses visible light fromlasers rather than radio waves.
Contents
[hide]
1 History
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2 Applications
3 Principles
o 3.1 Reflection
o
3.2 Radar equation o 3.3 Doppler effect
o 3.4 Polarization
o 3.5 Limiting factors
3.5.1 Beam path and range
3.5.2 Noise
3.5.3 Interference
3.5.4 Clutter
3.5.5 Jamming 4 Radar signal processing
o 4.1 Distance measurement
4.1.1 Transit time
4.1.2 Frequency modulation
o 4.2 Speed measurement
o 4.3 Pulse-Doppler signal processing
o 4.4 Reduction of interference effects
o 4.5 Plot and track extraction 5 Engineering
o 5.1 Antenna design
5.1.1 Parabolic reflector
5.1.2 Types of scan
5.1.3 Slotted waveguide
5.1.4 Phased array
o 5.2 Frequency bands
o 5.3 Radar modulators o 5.4 Radar coolant
6 See also
7 Notes
8 References
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9 Further reading
10 External links
[edit]History
Main article: History of radar
As early as 1886, Heinrich Hertz showed that radio waves could be reflected from solid objects. In
1895 Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an
apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap
transmitter. In 1897, while testing this in communicating between two ships in the Baltic Sea, he took note of
an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon
might be used for detecting objects, but he did nothing more with this observation.[3]
The German Christian Huelsmeyer was the first to use radio waves to detect "the presence of distant metallic
objects". In 1904 he demonstrated the feasibility of detecting a ship in dense fog but not its distance.[4] He
obtained a patent[5] for his detection device in April 1904 and later a patent[6] for a related amendment for
determining the distance to the ship. He also got a British patent on September 23, 1904[7] for the first full radar
application, which he called telemobiloscope .
A Chain Home tower in Great Baddow, United Kingdom
In August 1917 Nikola Tesla outlined a concept for primitive radar units.[8] He stated,
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Echo heights above ground
The radar beam would follow a linear path in vacuum, but it really
follows a somewhat curved path in the atmosphere because of the
variation of the refractive index of air, that is the radar horizon. Even
when the beam is emitted parallel to the ground, it will rise above it
as the Earth curvature sinks below the horizon. Furthermore, the
signal is attenuated by the medium it crosses, and the beam
disperses.
The maximum range of a conventional radar can be limited by a
number of factors:
Line of sight, which depends on height above ground.
The maximum non-ambiguous range which is determined by
thepulse repetition frequency. The maximum non-ambiguous
range is the distance the pulse could travel and return before
the next pulse is emitted.
Radar sensitivity and power of the return signal as computed in
the radar equation. This includes factors such as
environmentals and the size (or radar cross section) of thetarget.
[edit]Noise
Signal noise is an internal source of random variations in the signal,
which is generated by all electronic components. Noise typically
appears as random variations superimposed on the desired echo
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Pulse radar: The round-trip time for the radar pulse toget to the target and return is measured. The
distance is proportional to this time.
Continuous wave (CW) radar
One way to measure the distance to an object is to transmit a short
pulse of radio signal (electromagnetic radiation) and measure the
time it takes for the reflection to return. The distance is one-half the
product of the round trip time (because the signal has to travel to the
target and then back to the receiver) and the speed of the signal.
Since radio waves travel at the speed of light, accurate distance
measurement requires high-performance electronics. In most cases,
the receiver does not detect the return while the signal is being
transmitted. Through the use of a duplexer, the radar switches
between transmitting and receiving at a predetermined rate. A similar
effect imposes a maximum range as well. In order to maximizerange, longer times between pulses should be used, referred to as a
pulse repetition time, or its reciprocal, pulse repetition frequency.
These two effects tend to be at odds with each other, and it is not
easy to combine both good short range and good long range in a
single radar. This is because the short pulses needed for a good
minimum range broadcast have less total energy, making the returns
much smaller and the target harder to detect. This could be offset by
using more pulses, but this would shorten the maximum range. Soeach radar uses a particular type of signal. Long-range radars tend
to use long pulses with long delays between them, and short range
radars use smaller pulses with less time between them. As
electronics have improved many radars now can change their pulse
repetition frequency, thereby changing their range. The newest
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Surveillance radar antenna
[edit]Types of scan
Primary Scan: A scanning technique where the main antenna
aerial is moved to produce a scanning beam, examples include
circular scan, sector scan etc.
Secondary Scan: A scanning technique where the antenna feed
is moved to produce a scanning beam, examples include
conical scan, unidirectional sector scan, lobe switching etc.
Palmer Scan: A scanning technique that produces a scanning
beam by moving the main antenna and its feed. A Palmer Scan
is a combination of a Primary Scan and a Secondary Scan.
[edit]Slotted waveguide
Slotted waveguide antenna
Main article: Slotted waveguide
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S 2 – 4 GHz 7.5 – 15 cm
Moderate range surveillance, Terminal
air traffic control, long-range weather,
marine radar; 'S' for 'short'
C 4 – 8 GHz 3.75 – 7.5 cm
Satellite transponders; a compromise
(hence 'C') between X and S bands;
weather; long range tracking
X 8 – 12 GHz 2.5 – 3.75 cm
Missile guidance, marine radar, weather,
medium-resolution mapping and ground
surveillance; in the USA the narrow
range 10.525 GHz ±25 MHz is used
for airportradar; short range tracking.Named X band because the frequency
was a secret during WW2.
Ku 12 – 18 GHz 1.67 – 2.5 cm high-resolution
K 18 – 24 GHz1.11 –
1.67 cm
from German kurz, meaning 'short';
limited use due to absorption by water
vapour, so Ku and Ka were used insteadfor surveillance. K-band is used for
detecting clouds by meteorologists, and
by police for detecting speeding
motorists. K-band radar guns operate at
24.150 ± 0.100 GHz.
Ka 24 – 40 GHz0.75
–
1.11 cm
mapping, short range, airport
surveillance; frequency just above K
band (hence 'a') Photo radar, used to
trigger cameras which take pictures of
license plates of cars running red lights,
operates at 34.300 ± 0.100 GHz.
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mm40 –
300 GHz
7.5 mm –
1 mm
millimetre band, subdivided as below.
The frequency ranges depend on
waveguide size. Multiple letters are
assigned to these bands by different
groups. These are from Baytron, a nowdefunct company that made test
equipment.
V 40 – 75 GHz 4.0 – 7.5 mmVery strongly absorbed by atmospheric
oxygen, which resonates at 60 GHz.
W 75 – 110 GHz
2.7 –
4.0 mm
used as a visual sensor for experimental
autonomous vehicles, high-resolutionmeteorological observation, and imaging.
UWB1.6 –
10.5 GHz
18.75 cm –
2.8 cm
used for through-the-wall radar and
imaging systems.
[edit]Radar modulators
Modulators act to provide the waveform of the RF-pulse. There are
two different radar modulator designs:
high voltage switch for non-coherent keyed power-
oscillators[28] These modulators consist of a high voltage pulse
generator formed from a high voltage supply, a pulse forming
network, and a high voltage switch such as a thyratron. They
generate short pulses of power to feed the e.g. magnetron, a
special type of vacuum tube that converts DC (usually pulsed)
into microwaves. This technology is known as pulsed power. In
this way, the transmitted pulse of RF radiation is kept to a
defined, and usually, very short duration.
hybrid mixers,[29] fed by a waveform generator and an exciter for
a complex but coherent waveform. This waveform can be
generated by low power/low-voltage input signals. In this case
the radar transmitter must be a power-amplifier, e.g. aklystron
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tube or a solid state transmitter. In this way, the transmitted
pulse is intrapulse-modulated and the radar receiver must
use pulse compression technique.
[edit]Radar coolant
Coolanol (silicate ester) was used in several military radars in the
1970s. However, it is hygroscopic, leading to formation of highly
flammable alcohol. The loss of a U.S. Navy aircraft in 1978 was
attributed to a silicate ester fire.[30] Coolanol is also expensive and
toxic. The U.S. Navy has instituted a program named Pollution
Prevention (P2) to reduce or eliminate the volume and toxicity of
waste, air emissions, and effluent discharges. Because of this
Coolanol is used less often today.
PAO is a synthetic lubricant blend of a polyol ester mixed with
effective amounts of an antioxidant, yellow metal pacifier and rust
inhibitors. Effective additives include secondary arylamine
antioxidants, triazole derivative yellow metal pacifier and anamino
acid derivative and substituted primary and secondary amine and/or
diamine rust inhibitor.
[edit]See also
Electronics portal
Nautical portal
Main article: Radar configurations and types
Acronyms and abbreviations in avionics
Definitions
Amplitude-comparison monopulse
Constant false alarm rate
Sensitivity Time Control
Hardware
Radar engineering details
Klystron
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Cavity magnetron
Radio
Traveling-wave tube
Crossed-field amplifier
Gallium arsenide
Similar detection and ranging methods
LIDAR
LORAN
Sonar
Historical radars
List of radars SCR-270 radar
H2S radar
[edit]Notes
1. ^ NASA. "RADAR means: Radio Detection
and Ranging". Nasa Explores . Archivedfrom the originalon 2007-10-14.
2. ^ "Radar definition in multiple dictionaries". Answers.com. Retrieved 2008-10-09.
3. ^ Kostenko, A. A., A. I. Nosich, and I. A.
Tishchenko, "Radar Prehistory, SovietSide," Proc. of IEEE APS International
Symposium 2001, vol.4. p. 44, 2003
4. ^ Christian Hülsmeyer by Radar World
5. ^ Patent DE165546; Verfahren, um
metallische Gegenstände mittels elektrischer
Wellen einem Beobachter zu melden.
6. ^ Verfahren zur Bestimmung der Entfernung
von metallischen Gegenständen (Schiffen o.
dgl.), deren Gegenwart durch das Verfahren
nach Patent 16556 festgestellt wird.
7. ^ GB 13170 Telemobiloscope
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8. ^ The Electrical Experimenter, 1917
9. ^ Post-War Research and Development ofRadio Communication Equipment
10.^ Radar
11.^ Jr. Raymond C. Watson (2009-11-25). Radar Origins Worldwide: History of Its
Evolution in 13 Nations Through World War
II . Trafford on Demand Pub. ISBN 978-1-4269-2111-7.
12.^ https://reader009.{domain}/reader009/html5/0508
13.^ FR 788795 Nouveau système de repérage
d'obstacles et ses applications
14. ̂ a
b
(French) Copy of Patents for theinvention of radar on www.radar-france.fr
15.^ Hearst Magazines (1935-12). Popular
Mechanics . Hearst Magazines. p. 844.
16.^ John Erickson. Radio-Location and the AirDefence Problem: The Design andDevelopment of Soviet Radar. ScienceStudies, Vol. 2, No. 3 (Jul., 1972), pp. 241-
26317.^ Page, Robert Morris, The Origin of Radar ,Doubleday Anchor, New York, 1962, p. 66
18.^ Bonnier Corporation (1935-10). Popular
Science . Bonnier Corporation. p. 29.
19.^ Goebel, Greg (2007-01-01). "The Wizard
War: WW2 & The Origins Of Radar". Retrieved 2007-03-24.
20. ̂ a b Alan Dower Blumlein (2002). "The storyof RADAR Development". Retrieved 2011-05-06.
21.^ British man first to patent radar officialsite of thePatent Office
[dead link ]
22.^ GB 593017 Improvements in or relating to
wireless systems
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23.^ Bonnier Corporation (1941-12). Popular
Science . Bonnier Corporation. p. 56.
24. ̂ a b Hearst Magazines (1941-09). Popular
Mechanics . Hearst Magazines. p. 26.
25. ̂ a b "Ground Surveillance Radars andMilitary Intelligence". Syracuse ResearchCorporation; Massachusetts Institute ofTechnology.
26.^ "AN/PPS-5 Ground Surveillance Radar". You Tube; jaglavaksoldier's Channel.
27.^ MiG-31 FOXHOUND
28.^ Radartutorial
29.^ Radartutorial 30.^ Stropki, Michael A.
(1992). "Polyalphaolefins: A New ImprovedCost Effective Aircraft Radar Coolant". Melbourne, Australia: Aeronautical ResearchLaboratory, Defense Science andTechnology Organisation, Department ofDefense. Retrieved 2010-03-18.
[edit]References Barrett, Dick, "All you ever wanted to know about British air
defence radar ". The Radar Pages. (History and details of
various British radar systems)
Buderi, "Telephone History: Radar History ". Privateline.com.
(Anecdotal account of the carriage of the world's first high power
cavity magnetron from Britain to the US during WW2.)
Ekco Radar WW2 Shadow Factory The secret development ofBritish radar.
ES310 "Introduction to Naval Weapons Engineering.". (Radar
fundamentals section)
Hollmann, Martin, "Radar Family Tree ". Radar World.
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MIT Video Course: Introduction to Radar Systems A set of 10
video lectures developed at Lincoln Laboratory to develop an
understanding of radar systems and technologies.
Popular Science , August 1943, What Are the Facts About
RADAR one of the first detailed factual articles on radar history,
principles and operation published in the US
"The Great Detective", 1946. Story of the development of radar
by the Chrysler Corporation
Christian Hülsmeyer and the early days of radar
Radar: The Canadian History of Radar - Canadian War Museum
Radar technology principles
History of radar
Radar invisibility with metamaterials
Radar Research Center-Italy
Early radar development in the UK
Principles of radar target acquisition and weapon guidance
systems
Cloaking and radar invisibility
The Secrets of Radar Museum
84th Radar Evaluation Squadron
Radar
EKCO WW II ASV radar units
RAF Air Defence Radar Museum
Radar - A case study highlighting the vital contribution physics
research has made to major technological development
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