RADAR & ARPA

Ibrahim Al Jabberi09109343

Radar is a acronym for: Radio Detection And Ranging.

System consists of Electronic + Mechanical units that work together in a synchronization way for transmitting electromagnetic signals in the form of pulses and receiving echoes from objects of interest (targets) - To determine the targets Range and Bearing Marine radar system can provide very useful navigation information in a variety of situations. When a vessel is within radar range of land or special radar aids to navigation, the navigator can take distances and angular bearings to charted objects and use these to establish arcs of position and lines of position on a chart. A fixconsisting of only radar information is called a radar fix.

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.

The German Christian Huelsmeyer was the first to use radio waves todetect "the presence of distant metallic objects". In 1904 he demonstrated the feasibility of detecting a ship in dense fog but not its distance. He obtained a patent for his detection device in April 1904 and later a patent for a related amendment for determining the distance to the ship. He also got a British patent

on September 23, 1904 for the first full radar application, which he called telemobiloscope.

In August 1917 Nikola Tesla outlined a concept for primitive radar units. He stated,

"...by their [standing electromagnetic waves] use we may produce atwill, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel atsea, the distance traversed by the same, or its speed."

In 1922 A. Hoyt Taylor and Leo C. Young, researchers working with the U.S. Navy, discovered that when radio waves were broadcast at 60 MHz it was possible to determine the range and bearing of nearbyships in the Potomac River. Despite Taylor's suggestion that this method could be used in darkness and low visibility, the Navy did not immediately continue the work. Serious investigation began eight years later after the discovery that radar could be used to track airplanes.

Before the Second World War, researchers in France, Germany, Italy,Japan, the Netherlands, the Soviet Union, the United Kingdom, and the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war.

In 1934 the Frenchman Émile Girardeau stated he was building an obstacle-locating radio apparatus "conceived according to the principles stated by Tesla" and obtained a patent for a working system, a part of which was installed on the Normandie liner in 1935.

During the same year, the Soviet military engineer P.K.Oschepkov, in collaboration with Leningrad Electrophysical Institute, producedan experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver. The French and Soviet systems, however, had continuous-wave operation and could not give the full performance that was ultimately at the center of modern radar.

Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by American

Robert M. Page, working at the Naval Research Laboratory.[17] The following year, the United States Army successfully tested a primitive surface to surface radar to aim coastal battery search lights at night. This was followed by a pulsed system demonstrated in May 1935 by Rudolf Kühnhold and the firm GEMA in Germany and then one in June 1935 by an Air Ministry team led by Robert A. Watson Watt in Great Britain. Later, in 1943, Page greatly improvedradar with the monopulse technique that was used for many years in most radar applications.

The British were the first to fully exploit radar as a defence against aircraft attack. This was spurred on by fears that the Germans were developing death rays. The Air Ministry asked British scientists in 1934 to investigate the possibility of propagating electromagnetic energy and the likely effect. Following a study, they concluded that a death ray was impractical but that detection of aircraft appeared feasible. Robert Watson Watt's team demonstrated to his superiors the capabilities of a working prototype and then patented the device. It served as the basis for the Chain Home network of radars to defend Great Britain. In April 1940, Popular Science showed an example of a radar unit using the Watson-Watt patent in an article on air defence, but not knowing that the U.S. Army and U.S. Navy were working on radars with the same principle, stated under the illustration, "This is not U.S. Army equipment." Also, in late 1941 Popular Mechanics had an article in which a U.S. scientist conjectured what he believed the British early warning system on the English east coast most likely looked like and was very close to what it actually was and how it worked in principle.

The war precipitated research to find better resolution, more portability, and more features for radar, including complementary navigation systems like Oboe used by the RAF's Pathfinder.

Principle of operation:

- Radar uses electromagnetic energy Pulses - The returned energy is called an ECHO. - Radar sets use the echo to determine the Bearing and Range of the reflecting object.

• This energy normally travels through space in a straight line,at a constant speed, and will vary only slightly because ofatmospheric and weather conditions. – Range can be determined by measuring the time difference between transmission and reception– Relative Bearing (Angle )can be determined by measuring the angleof arrival (AOA) of the signal

A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected and/or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity—especially by most metals, by seawater, by wet land, and by wetlands. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either closer orfarther away, there is a slight change in the frequency of the radio waves, caused by the Doppler effect.

Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals.

The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, suchas visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent toradio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars except when detection of these is intended.

Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is

called illumination, regardless of the fact that radio waves are invisible to the human eye or cameras.

USES OF RADAR : • Determination of the target’s position. • Determination of the coast line & channels. • Fixing the ship near the coast.• To avoid collision.• Supply the officer of the watch by information. • In the Search & Rescue operation.

Advantages of using radars :- Used in good visibility to detect long range targets- Used In poor visibility to detect and discriminate closed

targets- Often has a longer range than other methods- A Fix could be obtained from just a single object- The uses of radarDisadvantages :• Subject to mechanical and electrical failure• There are maximum and minimum range limitations• Small objects aren’t always detected, especially in rough seas• Requires transmission from the ship• False echo’s may be appeared as result of ship’s construction

Electromagnetic waves :are formed when an electric field couples with a magnetic field. Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. The different names refer to different wavelengths• They are waves used in Radars.• They consist of a magnetic field and electric field having thesame frequency and wave length

Characteristic of the electromagnetic waves: It returns back when hits a solid object. Travel in space. Travel in a wave form (sin wave). Can be affected by the atmosphere. Speed of (3 x 108 m/sec) = (300 m/µs) = (300,000 Km/sec) =(162000 NM/sec)

Wave length: -It’s the distance between two top or two bottoms measured by meter

units.

• Frequency : the no. of oscillations (cycles) in 1 sec. X BAND 3.2cm 9300 to 9500 MHz S BAND 10cm 2900 to 3100 MHz Kinds of Radio Transmission :– 1-Continuous wave(C.W) 2-Amplitude Modulation(A.M) 3-Frequency Modulation (F.M) 4-Pulse Modulation(P.M) • The radar pulse is: The electromagnetic energy transmitting out of the scanner in the form of PULSESPulse Diagram:

Pulse Length(PL) - PULSE WIDTH (PW):PL: -The duration of the transmitted radar pulse (0.05 to 1.3 µsec) Higher frequencies give shorter pulse width which allow the radar to detect smaller objects at longerREST TIME: = PRI – PL = PRI - PW (the reception time or listeningtime or the off time)Pulse Repetition Interval (PRI): PRI =PRT =PRP (250 to 2500µsec)Pulse Repetition Interval (PRI) = Pulse Repetition Time (PRT) = Pulse Repetition Period (PRP)The time between the starting (beginning) of two consecutive pulses.

Pulse Repetition Frequency (PRF) = Pulse Repetition Rate

(PRR) : The number of pulses of RF energy transmitted per second In marine radar (400 to 4000 pulse/ sec)

PRI=PRT=PRP

PL / PW

“Receiving -Time

PRI=PRT=PRP=1/PRF=1/PRR

Carrier Freq.

P.R.F. changes with the changing of range: In short ranges High P.R.F. In long ranges Low P.R.F

RELATION BETWEEN (P.R.I.) & (P.R.F.)• On increasing the P.R.F. the P.R.I. decreases ( InverseRelation) P.R.I. X P.R.F. = 1• (PRI) is equal to the reciprocal of (PRF)as follows: PRI = 1/PRF

- The characteristics of the marine radar on merchant ships according to IMO requirements:- • Wave Length(λ) = 3.2 cm (X-band), 10cm (S-band)• P.L.(t) = 0.05 ~ 1.3 µs (short pulse ≤6M,long pulse≥12M)• PRI= 2502500 µs• PRF= PRR = 4000400 pulse/second• F = 9300 ~ 9500 MHz ,2900 ~ 3100MHz• Horizontal Beam Width ≤ 2.5º, actually 0. 5º : 2.5 º• Transmitted Power: LowHigh• The Using: Short Range Long RangeRough sea Clear seaBetter Discrimination Bad Discrimination poor visibility good visibility good visibility to detect long range targets (S-band) poor visibility to detect and discriminate closed targets (X-band)

- Principle of Range Measurement :

The transmitter send out short powerful electro-magnetic energy called Pulse by using antenna These pulse travel at the speed of light When strike any object they are reflected back to the scanner as echo. The receiver processes echo and cause it to show up visually as a bright spot onthe screen (PPI)

• Pulse is scattered or reflected and detected at the Radar as echo.- By knowing the speed of electromagnetic waves and Time

between emitted and returned pulse gives the RangeR = C * t / 2

- There is one trace created for every Pulse. -The tracing spot leaves the center. At the same instant that the pulse leaves the scanner. -The tracing spot is move at a speed = ½ radio wave speed - 150 meters per micro-second- Methods of Range Measurements : 1- Fixed Range Rings (FRR): Calibration rings are made to appear centered over the PPI each range rings represents a definite value of range so the range of target can be visually estimated. 2- Variable Range Marker (VRM): A circle with a variable radius controlled by a rotary knob. The value of radius in miles and decimal of mile and indicated by adigital display.3- Free Electronic Range and Bearing Line:Electronic line used to measure targets range and bearing (one switch or two /one indicator or two) Principle of Bearing Measurement:

The marine radar use one antenna in both transmission and receptionoperation The pulses sent out by the scanner are beamed in one direction at a time.Narrow horizontal beam width (HBW) 0.5º ÷2.5º The vertical beam width according to the I.M.O must be from 20 0 to 30 0 - The scanner is made to rotate clockwise at a very constant speed (20-30 RPM) - The PRF is so high (400-4000 P/S) compared to RPM - The Base Time Line (TBL) on the screen also rotates and issynchronized with the scanner.- The energy is propagated in pulsed form in the direction of theantenna witch rotates in synchronization with TBL in the displayunit - And when the energy hits targets it reflected in all direction

And a part of that energy return back in the same direction of transmission witch received by the scanner and appear as spot point on the TBL which its relative direction is equals to the relative antenna direction from the ships heading up

• Methods of Bearing Measurement: 1-Mechanical curser 2-Electronic Bearing Line (EBL) 3-Parallel Index 4- Joystick and Screen MarkerRadar Bearing:1-The TRUE BEARING 2- RELATIVE BEARING HORIZONTAL BEAM WIDTH : To obtain an accurate bearing for a target on the radar screen, the H.B.W must be very small: 1- Concentration of the energy in a certain direction.

2- Bearing Discrimination According to the I.M.O requirement the H.B.W must between 0.50 to 2.50. HBW = K x wave length in mete / width of the scanner (K = 70) • VERTICAL BEAM WIDTH : The vertical beam width according to the I.M.O must be from 200 to 300: 1- To keep on the radar performance during pitching and rolling. 2- For detection the targets near the ship. UNITS OF MARINE RADAR:1) The transmitter.2) The aerial – Scanner - Antenna.3) The receiver.4) The display unit.

1- TRANSMITTER The main function of the transmitter is to create electromagneticenergy in the form of pulses having special characteristics asmaintained before. These pulses are moved to the scanner through a pipe (wave guide)OR COAXIAL CABLE. For every pulse created by the transmitter there is an electroncreated to hit the underside of the PPI and moves from the center

to the edge of the screen at a number of times per sec. equal tothe P.R.F creating a line called the trace line 2- THE AERIAL – ANTENNA - SCANNER:The function of the SCANNER: Is to send out the pulses in all directions & receives the echofrom the targets. It is designed so as to send out the energy in the form of abeam having a vertical & horizontal beam width Types: The parabolic antenna The Slotted waveguide antenna. 3- THE RECEIVER The receiver receives the echo from the target through the scanner

and processes it in shape and form suitable for presenting on the PPI.(Plane Position Indicator)

There is one scanner for transmitting and receiving also there is one pipe for transmitting and receiving so it might happen thatpart of the transmitter energy will be send from the transmitter tothe receiver and part of the received echo will be send to the transmitter, to avoid this a valve called T/R CELL (T/R switch –Duplexer) is placed over the pipe between the transmitter and the receiver. There are 2 signals are going to enter the receiver unit: 1- The echo signal. 2- The trigger signal. (To avoid sea clutter). 4- THE DISPLAY UNIT: The main function of the display unit is to determine the presence of the targets and display it on the screen as radar picture. To obtain a radar picture there are 4 signals must be enteredto the display unit: 1- The amplified echo. 2- The rotation signal. 3- The trigger signal. 4- The heading marker signal1- TRANSMITTER unit:

TRIGGER UNIT:• Is the unit responsible for the synchronization between units. • Generates electric pulse.• Send this electric pulse in the form of spike wave signals to themodulator & also to the time base unit in the receiver (the no. of the spike waves per sec.= the P.R.F)• It is sometimes referred to PRF Generator• It controls the P.R.F (Short range = High P.R.F) - (Longrange = Low P.R.F) MODULATOR UNIT: The function of the Modulator is to produce a pulse of the correct length, power and shape• Changes the spike waves coming from the trigger unit to highpower pulses- (SQUARE PULSE) - Controls the P.L.MAGNETRON UNIT:• Is a high power RF oscillator capable of being switched on and off for short duration (equal to the PL) at the desired P.R.F by the pulse from the modulator.• Changes the pulse coming out from the modulator to electromagnetic pulse

• The output of the magnetron consists of RF pulse of electromagnetic energy (high frequency Pulse) which is sent to the scanner.

2- THE ANTENNA:• The Antenna unit consist of: 1- Wave guide OR coaxial cable 2- TR / RX switch 3- The scanner 2-1- Wave guide:Used as a medium for high energy shielding. Carries the RF pulses from magnetron to scanner also from the scanner to the mixer 2-2- TR / RX switch(T/R CELL- Duplexer):Is placed over the pipe between the transmitter and the receiver. 2-3- The Scanner: The scanner this is a unidirectional aerial which beams the energy and receive the echoes. The beam should be narrow in the horizontal plane and wide in the vertical plane Scanner must rotate at a constant RPM 20÷ 30 not less than 12 in relative wind speed up to 100 kns Scanner motor situated just under the scanner 3- THE RECEIVER:

FUNCTION OF THE RECEIVER:• The function of the receiver is to receive the echo from thetarget, amplify it to be shown on the radar screen

• Because the freq. of the received echo is very high and of lowpower that can not be amplified so this freq. must be reduced before being amplified • The units responsible for this operation is :• 1 – magnetron 2- Mixer 3- Local Oscillator. To produce the intermediate frequency. (30 to 60MHz)• This I.F passes to the I.F. multistage amplifier then to thedetector to remove the outer shell (Envelope) of the pulse andchange it to video pulse.• The video pulse then passes to the multistage video amplifier.• This amplified video signals passes to the Cathode Ray Tube(C.R.T.) LOCAL OSCILLATOR:• Oscillate at a constant low power RF(30 TO 60) above or belowthe magnetron freq. (usually below) • The difference between this freq. And the magnetron freq. iscalled the I.F. I.F. = Magnetron freq. – Local Osc.freq.MIXER:• Receives the echo (low power and high freq.) and mix it with the local oscillator freq. to produce the I.FTUNING CONTROL: The tuning unit control the local oscillator freq. to obtain the most suitable I.F and also the best radar Picture and this is don by changing the electric potential which is feeding the local oscillator to increase or decrease the local oscillator freq. IF AMPILFIER:• Amplifies I.F received from the mixer several times & reduces theclutter.• Note that on amplifying the echo of the target the clutters also will be amplifiedGAIN CONTROL: Controls the amplification process.Anti Clutter Control : Controls the clutter coming in with the target’s echo.DETECTOR:

• Remove the outer shell (Envelope) of the received echo and change it to video pulse.4- THE DISPLAY UNIT:• The main function of the display unit is to determine the presenceof the targets and display it on the screen as radar picture.4-1 - Cathode Ray Tube - CRT 4-2- Time base unit4-3- Deflection coils 4-4- Trace blanking unit

ARPA : Automatic Radar Plotting AidThe availability of low cost microprocessors and the development ofadvanced computer technology during the 1970s and 1980s have made itpossible to apply computer techniques to improve commercial marine radarsystems. Radar manufactures used this technology to create the AutomaticRadar Plotting Aids (ARPA). ARPAs are computer assisted radar dataprocessing systems which generate predictive vectors and other shipmovement information.

The International Maritime Organization (IMO) has set out certainstandards amending the International Convention of Safety of Life at Searequirements regarding the carrying of suitable automated radar plotting aids(ARPA). The primary function of ARPAs can be summarized in thestatement found under the IMO Performance Standards. It states arequirement of ARPAs....“in order to improve the standard of collisionavoidance at sea: Reduce the workload of observers by enabling them toautomatically obtain information so that they can perform as well withmultiple targets as they can by manually plotting a single target”. As we cansee from this statement the principal advantages of ARPA are a reduction inthe workload of bridge personnel and fuller and quicker information onselected targets.

A typical ARPA gives a presentation of the current situation and usescomputer technology to predict future situations. An ARPA assessesthe riskof collision, and enables operator to see proposed maneuvers by own ship.While many different models of ARPAs are available on the market, thefollowing functions are usually provided:

1. True or relative motion radar presentation.2. Automatic acquisition of targets plus manual acquisition3. Digital read-out of acquired targets which provides course, speed, range,bearing, closest point of approach (CPA, and time to CPA (TCPA).4. The ability to display collision assessment information directly on thePPI, using vectors (true or relative) or a graphical Predicted Area ofDanger (PAD) display.5. The ability to perform trial maneuvers, including course changes, speedchanges, and combined course/speed changes.6. Automatic ground stabilization for navigation purposes.ARPA processes radar information much more rapidly than conventionalradar but is still subject to the same limitations. ARPA data is only asaccurate as the data that comes from inputs such as the gyro and speed log.

STAND-ALONE AND INTEGRAL ARPA’s

Over the past 10 years, the most significant changes to the ARPA systemshas been in their design. The majority of ARPAs manufactured todayintegrate the ARPA features with the radar display.The initial development and design of ARPAs were Stand-alone units.That is they were designed to be an addition to the conventional radar unit.

All of the ARPA functions were installed on board as a separate unit butneeded to interfaced with existing equipment to get the basic radar data. Theprimary benefits were cost and time savings. This of course was not the mostideal situation and eventually it was the integral ARPA that graduallyreplaced the stand-alone unit.The modern integral ARPA combines the conventional radar data withthecomputer data processing systems into one unit. The main operationaladvantage is that both the radar and ARPA data are readily comparable.

ARPA DISPLAYFrom the time radar was first introduced to the present day the radarpicture has been presented on the screen of a cathode ray tube. Although thecathode ray tube has retained its function over the years, the wayin whichthe picture is presented has changed considerably. From about the mid-1980sthe first raster-scan displays appeared. The radial-scan PPI was replaced by araster-scan PPI generated on a television type of display. The integral ARPAand conventional radar units with a raster-scan display will gradually replacethe radial-scan radar sets.The development of commercial marine radar entered a new phase in the1980s when raster-scan displays that were compliant with the IMOPerformance Standards were introduced.The radar picture of a raster-scan synthetic display is produced on atelevision screen and is made up of a large number of horizontal lines which

form a pattern known as a raster. This type of display is much more complexthan the radial-scan synthetic display and requires a large amountofmemory. there are a number of advantages for the operator of a raster-scandisplay and concurrently there are some deficiencies too. The mostobviousadvantage of a raster-scan display is the brightness of the picture. Thisallows the observer to view the screen in almost all conditions ofambientlight. Out of all the benefits offered by a raster-scan radar it is this abilitywhich has assured its success. Another difference between the radial-scanand raster-scan displays is that the latter has a rectangular screen. The screensize is specified by the length of the diagonal and the width and height of thescreen with an approximate ratio of 4:3. The raster-scan televisiontubeshave a much longer life than a traditional radar CRT. Although thetubes arecheaper over their counterpart, the complexity of the signal processingmakes it more expensive overall.

General Features· Daylight-bright high-resolution display· 28 inch diagonal CRT presents radar picture of 360 mm effective diameterwith alphanumeric data area around it· User friendly operation by combination of tactile backlit touchpads, atrackball and rotary controls· Audio-visual alert for targets in guard zone· Echo trail to assess targets’ speed and course by simulated afterglow· Electronic plotting of up to 10 targets in different symbols (This function

is disabled when ARPA is activated)· Electronic parallel index lines· Interswitch (optional) built in radar or ARPA display unit· Enhanced visual target detection by Echo Average, Echo Stretch,Interference Rejector, and multi-level quantization· Stylish display· Choice of 10, 25 or 50 KW output for X-band; 30 KW output for S-band,either in the transceiver aloft (gearbox) or RF down (transceiver in bridge)· Exclusive FURUNO MIC low noise receiver ARPA Features· Acquires up to 20 targets automatically· Movement of tracked targets shown by true or relative vectors (Vectorlength 1 to 99 min. selected in 1 min steps)· Setting of nav lines, buoy marks and other symbols to enhance navigationsafety· On-screen digital readouts of range, bearing, course, speed, CPA, TCPA,BCR (Bow Crossing Range) and BCT (Bow Crossing Time) of two targetsout of all tracked targets.· Audible and visual alarms against threatening targets coming intooperator-selected CPA/TCPA limits, lost targets, two guard rings, visualalarm against system failure and target full situation· Electronic plotting of up to 10 targets in different symbols (This functionis disabled when ARPA is activated)· Electronic parallel index lines· Interswitching (optional) built in radar or ARPA display unit· Enhanced visual target detection by Echo Average, Echo Stretch,Interference Rejector, and multi-level quantization· Stylish display· Choice of 10,25 or 50 kW output for X-band; 30kw output for S-band,either in the transceiver aloft (gearbox) or RF down (transceiver in bridge)

· Exclusive FURUNO MIC low noise receiver