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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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