Fundamentals_of_Radarr key points required

Radar

1. FUNDAMENTALS OF RADAR BY ANNE ROSE AMET CITY COLLEGE

2. USES OF RADAR The two main uses of Radar are, Assists in Safe Navigation Assists in Collision Avoidance HOW DOES RADAR WORK? It consists of 3 units MARINE RADAR Marine radars are the best collision avoidance system ever developed for the recreational boater. Radar systems  let you “see” through darkness, fog and stormy weather conditions .

3. BLOCK DIAGRAM OF RADAR WAVE GUIDE The scanner is rotating with the RPM(Revolution per minute) of 20 to 30. The Scanner with the help of a transceiver it is transmitting short burst of electromagnetic energy and this are having a speed of light which is 3 x 10 8 meters per second.

4. BLOCK DIAGRAM OF RADAR MAGNETRON Equipment which converts Electrical Energy into Electromagnetic Energy . Equipment which produces Electromagnetic Energy. The Electromagnetic Energy with the help of transmitter and scanner it goes out and throw the radar beam in a unidirectional form.

5. The Electromagnetic Energy transmitting out from the Scanner to the target is called pulses. This travels at the Speed of Light. The Pulses after hitting the target reflect back in the form of Echoes. The reflected Echoes are received in the Receiver. The Receiver process the echoes and displays the target in the Radar. (some echoes will not reflect back depending on the shape of the target)

6. The Rectangular area is Display Unit. The Circular area is PPI (Plan Position Indicator) Heading Marker , Ship Position, Target HOW DOES RADAR POINTS A TARGET ON PPI Speed of the Electromagnetic Energy i.e. Speed of the Pulse is 3 x 10 8 m/s Speed of the Tracing Point moving radially in the direction same as the direction of Electromagnetic Energy. Speed of the Tracing Point is half of the Speed of the Pulse. Assume Range – 1 NM

7. Now, the echo has reached the receiver with the speed of 2 NM. When the receiver process the Echoes, the target in the Radar gets flattened and Brightened. This is how the Radar points the target on PPI. HOW DOES RADAR POINTS A TARGET ON PPI

8. TRIGGER Sends spike waves signals to the modulator The number of spikes per second equals to the PRF ( Pulse repetition frequency). POWER SOURCE The required AC input, is usually provided: directly from the ship's mains, or through a transformer, or through a motor alternator, or through an inverter if the ship's mains are D.C. Stores the energy received from the power source. DELAY LINE

9. MODULATOR Enhance the strength of the signal without affecting the parameters It also switches the magnetron on and off as required.  Each spike wave from the trigger causes the modulator to release one powerful DC pulse (square wave of 10,000 to15,000 Volts) from the delay line to the magnetron.  The duration of each pulse is the PL and the number of pulses per second is the PRF (Pulse repetition frequency)

10. STRUCTURE OF MAGNETRON The anode of a magnetron is fabricated into a cylindrical solid copper block. The cathode and filament are at the center of the tube and are supported by the filament leads. The cathode of a magnetron provides the electrons through which the mechanism of energy transfer is accomplished. The cathode is located in the center of the anode and is made up of a hollow cylinder of emissive material (mostly Barium Oxide) surrounding a heater. The feeding wires of the filament must center the whole cathode.  The 8 up to 20 cylindrical holes around its circumference are resonant cavities. 

11. MAGNETRON The  magnetron  is a high-powered vacuum tube that works as a self-excited microwave oscillator. Crossed electron and magnetic fields are used in the magnetron to produce the high-power output required in radar equipment. It converts Electrical Energy into Electromagnetic Energy. Converts the electrical pulses received from the modulator into electromagnetic pulses. It produces Electromagnetic Energy i.e. RF Pulses. These multi-cavity devices may be used in radar transmitters as either pulsed or CW oscillators at frequencies ranging from approximately 600 to 95,000 megahertz.   The frequency range of 3 cm radar is 9300 to 9500 MHz - X band The frequency range of 10 cm radar is 2900 to 3100 MHz - S band  USES and Disadvantage Used in Microwave Oven The relatively simple construction has the disadvantage that the Magnetron usually can work only on a constructively fixed frequency.

12. WAVEGUIDE The pulses are transmitted to the scanner unit by the waveguide. A waveguide is hollow copper tubing, usually rectangular in cross section, having dimensions according to the wavelength of the carrier frequency. It carries the RF pulses from the magnetron to the scanner. It also carries the RF echoes from the scanner to the Mixer (through the TR Cell).  An electronic switch in the waveguide, called the transmit/receive cell (T/R) isolates the receiver during transmission to protect it from the high power of the transmission. In modern radars the waveguide and the T/R switch are usually located within the scanner unit. Area Its  area of cross-section depends on the wavelength - the larger the wavelength, the greater the area of cross-section and vice versa. Causes The length of the waveguide,  The number of bends that it takes, Damage done Water or dirt inside it,  all cause severe attenuation in the waveguide.  Resulting in considerable loss of transmitted power and also of echo strength.

13. TYPES OF WAVEGUIDE Circular Rectangular Twist 90 degree elbow Single Ridged Double Ridged

14. WAVE PROPAGATION IN WAVEGUIDE The waves are propagating through the Rectangular and Circular WaveGuide. The Blue lines represent the electric flux lines and the Red lines the magnetic flux lines.  RECTANGULAR CIRCULAR

15. WAVEGUIDE APPLICATION A waveguide is an electromagnetic feed line used in  microwave communications, broadcasting, and radar installations . The electromagnetic field propagates lengthwise. Waveguides are most often used with horn antenna s and dish antenna s.

16. SCANNER This is a unidirectional aerial that beams the energy, and receives the echoes, one direction at a time. Since it rotates at a constant speed, the entire area around it gets scanned regularly. The size and type of scanner determine the HBW (Horizontal beam width)and VBW (Vertical beam width)of the set and hence its aerial gain. Aerial Gain An Omni-directional aerial send out the energy equally in all directions and an unidirectional aerial would concentrate it as a beam in one direction.  Both transmit signals of the same power. Therefore at a given distance inside the beam, the field strength of an unidirectional aerial will be ‘n’ times stronger than the field strength of an omni-directional aerial.  This ratio, expressed in decibels·, is called the aerial gain of the scanner and it depends on the vertical size, horizontal size and type of scanner. As per Performance Standards for Navigational Radar (IMO), the scanner must rotate at a constant RPM of not less than 20 (and also stop and start) in relative wind speeds up to 100 knots.  The scanner motor situated just under the scanner is, therefore, very powerful. 

17. SAFETY MEASURES If the scanner is fouled by halyards or stays, or if prevented from rotating by icing, either the gears will get stripped or the motor would burn out in a few minutes.  To prevent icing up of the scanner axle during periods of non-use in very cold weather, some manufacturers provide a heater which should be switched on whenever necessary.  Some other manufacturers provide switching arrangements to enable the scanner to be kept rotating even when the set is switched off. The surface of the scanner should be periodically cleaned of salt, dust, etc by brushing off with a soft paintbrush or wiping with a cloth.  The scanner should never be painted, except under the supervision of the manufacturer's representatives, as ordinary paints would alter the surface characteristics and cause severe attenuation at the scanner.

18. TYPES OF RADAR SCANNERS There are Five types of Radar Scanners, Parabolic plate,  Parabolic mesh,  Cheese Double cheese and Slotted Waveguide Scanners. On modern merchant ships, only slotted Waveguide Scanners are used.

19. SLOTTED WAVEGUIDE SCANNER The Slotted Waveguide type of Scanner, is a horizontal length of waveguide with slots on one side and the other end is permanently closed. The numerous slots are very specific in size and shape, and very precisely spaced, depending on the exact wavelength used and cause the energy to go out as parallel rays. The slotted part of the waveguide has a weatherproof cover of corrosion resistant material, usually Perspex or fiber glass, to keep out water, salt and dirt without itself causing much attenuation.  This further reduces wind resistance. S Band – 12 feet long X Band – 9 feet to 6 feet.

20. TR CELL A gas filled switching tube consists of two electrodes in it with a small gap between them. The transmit/receive cell blocks the receiver branch of the waveguide during transmission so that the transmitted pulse, being of very high power (25 to 60 kW), cannot directly enter the mixer and damage it. It is necessary because we use the same waveguide and scanner for transmission and for reception. Soon after transmission is over, the TR cell allows the echoes that are received to pass into the receiver. The TR Cell is an electronic switch with no moving parts. A HT PD (high tension potential difference), of about 500 to 2000 Volts, is constantly maintained between these two electrodes but the current cannot flow between them because of the gap. Transmitter Receiver

21. MIXER AND LO (LOCAL OSCILLATOR) The echoes that are received are very weak and of radio frequency (RF).  In commercial marine radar, it is not practicable, for reasons of economy, to amplify these RF echoes directly.  The frequency of the echoes is considerably reduced to a value called the intermediate frequency (IF), before amplification is done. This is called the principle of the heterodyne. The original RF of (X Band) 3 cm radar is about 9300 to 9500 MHz and of 10 cm radar (S band) is about 2900 to 3100 MHz.  The local oscillator (LO) produces continuous low power RF oscillations above or below (usually below) the magnetron frequency, the difference being called the intermediate frequency (IF). In many marine radar sets, the local oscillator uses a valve of special construction called the klystron . The IF is around 30 to 60 MHz, in commercial marine radar. Both, the local oscillations and the echoes received, are fed to the crystal mix

22. THE IF AMPLIFIER The echoes returning from a target are weak and of greatly differing signal strengths.  Furthermore, they lose some of their strength while being processed through the mixer. The strongest echo may be as much as 10 8 times as strong as the weakest one.  The weakest one needs to be amplified about 10 9 times to be able to show up on the screen  The amount of amplification is controlled by the setting of the "gain" or "sensitivity" knob. If the stronger echoes are amplified to a large extent , they would appear too bright and smudge severely on the screen (called blooming ). 

23. The IF amplifier may be of the Linear Amplification type or the Logarithmic Amplification type Linear Amplification Type The IF amplifier has several stages, each stage amplifying by a certain amount.  The output of the first stage is the input of the second stage, and so on.  The output signals of the final stage would all be of equal strength and hence all targets would appear equally bright on the PPI, regardless of whether it is a navigational buoy or a large ship.

24. Logarithmic Amplification Type A parallel lead is taken after every stage of the IF amplifier. All these signals are joined together and then fed to the video amplifier.  The advantage of this system is, that contrast is available  between weak and strong echoes,  possibly between two strong echoes of different strengths,  between targets and sea-clutter and also between targets and rain echoes. Some radar sets have a control knob with positions marked 'LINEAR' and 'LOG', thereby giving the observer a choice of the system of amplification, depending on the existing circumstances.

25. Radiation Hazards A radome is a structure that protects microwave equipment from the environment . Radomes protect the antenna from weather and conceal antenna electronic equipment from view. They also protect nearby personnel from being accidentally struck by quickly rotating antennas.

26. Radome

27. What is inside a radome? Radomes are made of very light material, usually fiberglass . They are designed to not attenuate or disrupt the radar signal being transmitted. Occasionally, weather radars get hit by the storms they are trying to scan. Here, you can see what a severe thunderstorm can do to a radome when hit with very strong winds.

28. WHAT IS A WAVEFORM? Waveform is curve showing the shape of a wave at a given time. It is a representation of how alternating current ( AC) varies with time. Frequency : the number of cycles which pass a point in a given time (1 second) Symbol is f Cycles per second is given by a common name Hertz Speed of radio wave is f x lambda

29. Crest The highest surface part of a wave is called the crest. Trough The lowest surface part of the wave is the trough. Wave height The vertical distance between the crest and the trough is the wave height. Wavelength The horizontal distance between two adjacent crests or troughs is known as the wavelength . Radio waves are long waves, and can measure thousands of yards long from crest to crest . Symbol is lambda

30. Attenuation When we are sending a radar / electromagnetic wave in the form of a signal with variation in voltage the signal gets weak after travelling a certain distance. So with distance the strength of a signal becomes weak. This phenomenon is called as attenuation. Original Wave Attenuated wave

31. T Types of Waveforms Alternating current waveform If the alternating current flowing between two terminals A and B was plotted on a graph, flow A to B termed positive and that from B to A termed negative , the waveform obtained would be sinusoidal (like that of a sine curve). The number of waves per second is called the frequency. The unit of frequency is the Hertz (l Hertz = 1 wave per second).

32. Direct current waveform Once the power is switched on, the current increases from zero to maximum in a very short while and then stays at that value. When the current is switched off, it quickly falls back to zero.

33. Square waveform (DC) This is the waveform of an interrupted direct current . Each wave is a pulse and the number of pulses per second is called the pulse repetition frequency (PRF) or pulse recurrence rate (PRR). The waveform is not exactly square or rectangular as the angles are not exactly 90. This is because the current requires a small interval of time to go from zero to maximum and vice versa. The duration of each pulse is the PL. A square wave is a non-sinusoidal periodic waveform.

34. Spike waveform This waveform of an interrupted direct current but The pulse length is extremely small. The current goes from zero to maximum in a very short while but falls back to zero equally fast without remaining at the maximum value. This spike is repeated at regular intervals, as required.

35. Saw-tooth waveform Here the current goes from zero to maximum slowly but very steadily. On reaching the maximum value, it falls back to Zero immediately. The sawtooth wave is repeated at regular intervals, as required.

36. Vertical Beam Width (VBW) Vertical Beam Width (VBW)‏ VBW is  the vertical angle at the scanner contained between the upper and lower edges of the RADAR beam . 

37. Vertical Beam Width (VBW) If the angle of the Radar beam is more, the energy will get scattered t he beam could not go to a longer distance More angle, less range

38. Vertical Beam Width (VBW) If the angle of the Radar beam is less, the energy will get concentrated t he beam can go to a longer distance Less angle, more range Disadvantage If the angle of the Radar beam is small, it will lead to ignore the small targets nearby, because of the throwing of the beam at longer range.

39. Vertical Beam Width (VBW) The centre area of the Radar beam will have 100% intensity and energy. When the Upper edge and Lower edge get scattered, the energy of the radar beam get decreased further.

40. Horizontal Beam Width (HBW) Horizontal Beam Width (HBW)‏- HBW is  the horizontal angle at the scanner contained between the leading and trailing edges of the RADAR beam

41. Horizontal Beam Width (HBW) The amount of flattening and brightening of the target on PPI is calculated by ½ HBW ahead of the target and ½ HBW below the target.

42. For a point target, the size of the paint will be equal to the Horizontal beam width.

43. Radar Resolution Ability to detect two targets separately. It has two types Bearing Resolution Ranging Resolution Short Pulse When short pulse hits the target, it will hit every target individually Long Pulse When long pulse hits the target , both target comes under one Radar Beam.

44. Range Resolution

45. The two Echoes have Merged

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