Advanced Radio and Radar

1. Advanced Radioand Radar Part 5 Radar

2. Introduction As World War II approached, scientists and the military were keen to find a method of detecting aircraft outside the normal range of eyes and ears. They found one, and at first called it Radio Detection Finding (RDF), then changed it to RAdioDetection And Ranging (RADAR).

3. Introduction Radar fires powerful radio waves towards a target, and collects the reflected energy. Radar operators find the position of the target in terms of range & bearing. As well as range and bearing radar can also find another vital fact about a target aircraft – its height.

4. Radar Operations Many factors prevent efficient operation of a radar system: – Signals from radio, stars, the atmosphere. – Man-made signals from other radar transmitters, electrical apparatus and machinery. – Echoes from hills, buildings, sea, clouds, hail, rain and snow. – Shape and composition have an effect on its echo. Noise Interference Clutter Target Characteristics

5. Radar Operations Many factors prevent efficient operation of a radar system: Noise Much of this can be reduced by electronic techniques Interference Clutter Target Characteristics

6. Types of Radar There are basically two different types of radar, Primary and Secondary. Primary Radar relies solely on the energy that it has generated and radiated, being reflected back from the target – i.e. an echo. Secondary Radar has some co-operation from the target – the target generates its own ‘em’ radiation.

7. Primary Radar Primary radar systems may be found in ground, air, ship or space platforms, and are used in roles such as: Surveillance (including weather) Early Warning Navigation Ground Mapping (from space or aircraft) Guidance Control Target Detection and Tracking Terrain Following/Avoidance Collision Avoidance and Altitude Measurement Air Traffic Control

8. Primary Radar Radars operate in 2 different modes: Pulse-Modulated Radar (pulsed) and Continuous Wave Radar (CW). They operate in the Ultra High Frequency (UHF) or Super High Frequency (SHF) bands. This frequency depends on the radar function – Long range search radar operates on a relatively low frequency (UHF) while a weapons system fire control radar will operate at a very high frequency (SHF)

9. Primary Radar Pulse-Modulated Radar A pulsed radar uses an echo principle. The transmitter fires a pulse of energy and then "listens" for an echo to return. The pulses are transmitted at a rate which determines the range of the radar. This is called the Pulse Repetition Frequency (PRF). Fires pulse ‘Listens’ Return Echo

10. Primary Radar Pulse-Modulated Radar PRF ranges from 250pps for long-range radars to 2000pps for short-range radars. For long-range radar, 1 million watts (megawatt) of (RF) power is required. This power is used only during the brief transmission of the pulse. The transmitter then ‘rests’ until the next pulse, and the receiver ‘listens’ for an echo. Fires pulse ‘listens’ Fires pulse

11. Primary Radar Pulse-Modulated Radar To calculate the distance to the target, the time for a pulse to travel one mile and return is known as a "Radar Mile“. Target Range Range Return Echo Time 1 Kilometre 1000 m 6.67 ms (6μs) 1 Statute Mile 5280 ft 10.75 ms (10μs) 1 Nautical Mile 6080 ft 12.36 ms (12μs) So if we measure the elapsed time between the transmission and reception of a pulse, we can use the formula: Distance = Speed x Time

12. Primary Radar The Doppler Effect • Relative movement of a sound source • towards and away from a fixed point • causes frequency modulation in the sound wave. • This is a natural phenomenon Stretch Squeeze

13. Primary Radar The Doppler Effect • A radio transmission from an aircraft • would be affected in exactly the same way. • This is called the Doppler Effect. Stretch Squeeze

14. Primary Radar Continuous Wave Radar (CW) There are two basic types of CW radar. Continuous Wave Doppler (CW Doppler) and Frequency-Modulated Continuous Wave (FMCW).

15. Primary Radar Continuous Wave Radar (CW) When the radar sends out a pulse, if the target is moving towards the transmitter the reflected waves become bunched up. (i.e. they acquire a higher frequency) (and vice versa if the target is moving away). (i.e. they acquire a lower frequency) CW Doppler

16. Primary Radar Continuous Wave Radar (CW) CW Doppler The radar equipment is able to detect these small changes in frequency shifts and so determine the target’s velocity (speed and direction) with respect to the transmitter. A similar system is used by traffic police with their "speed gun". This is called the Doppler Effect.

17. Primary Radar Continuous Wave Radar (CW) Frequency-Modulated CW Radar is a short range measuring radar capable of determining distance. It is often used as a “radar altimeter” to measure the exact height during the landing procedure of aircraft, and as early-warning radar, and proximity sensors.

18. Primary Radar Continuous Wave Radar (CW) Frequency-Modulated CW Radar The signal is transmitted over a fixed band, and made to vary in frequency in a controlled cyclic manner with respect to time. By measuring the frequency of the returning echo it is possible to calculate the time interval elapsed since that frequency was transmitted, and thus the target’s range.

19. Primary Radar Block diagram of a typical radar installation. Master Timing Unit (MTU) Produces regular, timed pulses, controlling the start of the timebase generator . Timebase Generator Provides the reference signal for the start of the transmit sequence. Transmitter (Tx) Produces high energy RF pulses in the range of 400 MHz to 40GHz. M T U TX Timebase Generator

20. Primary Radar Block diagram of a typical radar installation. Transmit/Receive Switch Switches both the transmitter and receiver “ON” and “OFF”. Aerial Used to launch the RF pulses and collect the returns for processing. Receiver (Rx) Collects and amplifies the returning echoes and produces video pulses to the display. CRT (Cathode Ray Tube) Displays targets to the operator. RX T/R Switch C R T Indicator M T U TX Timebase Generator

21. Primary Radar Block diagram of a typical radar installation. Master Timing Unit (MTU) Timebase Generator Transmitter (Tx) Transmit/Receive Switch Aerial Receiver (Rx) CRT (Cathode Ray Tube) RX T/R Switch C R T Indicator M T U TX Timebase Generator

22. Secondary Radar It is vital to know the identity of aircraft displayed on an air traffic controller’s screen. Identification Friend or Foe (IFF) is such a method. Aircraft are fitted with a transmitter/receiver (transponder) which resubmits a reply signal to an interrogating transmitter/receiver (interrogator). IFF equipment is specifically for military use, the civilian version is called SSR, Secondary Surveillance Radar

23. Secondary Radar The IFF/SSR systems can obtain specific information from an aircraft. The aircraft is interrogated on 1030 MHz using coded pulses or modes. The aircraft responds on 1090 MHz using a standard system of codes. There are 3 modes in use: Mode 1 Military Aircraft Identify Mode 2 Military Mission Identify Mode 3 A) Common Military/Civilian Aircraft Identify B) Civil Identify C) Height Encoded Data

24. Secondary Radar IFF/SSR systems provide Air Traffic with information about particular aircraft – far exceeding that of primary radar. The types of information available are: Aircraft height The aircraft can also send emergency information such as: Loss of radio communications (code 7600) Hijack (code 7500) SOS (code 7700) (direct from aircraft’s altimeter) Direction, Speed and Type of aircraft.

25. Secondary Radar The main advantages of IFF/SSR over primary radar are: No clutter problems (i.e. unwanted returns from rain clouds and mountains) since transmitter and receiver operate on different frequencies. b. Increased range with less transmitted power, as the radio waves only have to travel one way. c. More information from each target. d. Ability to use wide bandwidth receivers.

26. Check of Understanding What does RADAR stand for? Ranging and direction radio Radio detection and ranging Ranging and detection radio Radio direction and ranging

27. Check of Understanding Radar detects a target by calculating its . . . Bearing, Height and Size Bearing, Height and Range Height, Range and Velocity Height, Range and Azimuth

28. Check of Understanding In this diagram What does the block ‘T’ represent? Timebase Generator Rx Unit Master Timing Unit Tx Unit

29. Check of Understanding A technique for minimising clutter in a radar system is: Increased use of the PRF Increased electronic countermeasures Reduction of aerial scanning speed Reduced by electronic techniques

30. Check of Understanding What is the time used in rough calculations when working in Nautical miles? 1μs 6μs 10μs 12μs

31. Check of Understanding The definition of a primary radar is one which: Is designed to detect targets at the longest possible range Utilises the change in frequency of reflected waves Receives no co-operation from the target and relies upon reflection only Transmits waves which vary in frequency at a controlled rate

32. Check of Understanding In this diagram What does the block ‘Q’ represent? Timebase Generator Rx Unit Master Timing Unit Tx Unit

33. Check of Understanding If a radar energy wave hits a target and returns with a frequency increase, what effect is being used? Demodulation Frequency Modulation Pulsed Frequency Doppler

34. Check of Understanding If the frequency of a reflected wave of a doppler radar decreases slightly, What is the target doing? Approaching Climbing towards the radar Moving away Descending towards the radar

35. Check of Understanding What is the time unit used in rough calculations when working in statue miles? 10μs 12μs 15μs 6μs

36. Check of Understanding In this diagram What does the block ‘S’ represent? Master Timing Unit Rx Unit T/R Switch Tx Unit

37. Check of Understanding The unit in a secondary radar which re-transmits the signals is called the . . . Interrogator Transponder Coding Unit Transmit-receive switch

38. Check of Understanding Which of the following is a type of Primary Radar? Cyclic Wave Inter-pulsed Wave Continuous Wave Carrier Wave

39. Check of Understanding Which of these factors affects radar performance? Clutter Frequency Height of Target Speed of Target

40. Check of Understanding In this diagram What does the block ‘V’ represent? Timebase Generator CRT Indicator Rx Unit Tx Unit

41. Check of Understanding What does SSR stand for? Single side radar Secondary side radar Single surveillance radar Secondary surveillance radar

42. Check of Understanding What is IFF used for? Alerts ATC of the direction of flight. Tells everyone you are friendly. Tells other pilots your aircraft is airworthy. Tells the pilot how many passengers are on board.

43. Check of Understanding A pulse radar calculates the target range by using what? A pulse long enough to reach the target Time between transmission and receipt of the pulse A pulse strong enough to reach the target Time between the transmitted pulses

44. Check of Understanding In this diagram What does the block ‘R’ represent? Master Timing Unit Rx Unit T/R Switch Tx Unit

45. Check of Understanding Secondary Radar is defined as a system . . . Which operates when the primary radar fails Where the target responds with its own echo Where the target absorbs the transmitted energy Where the target reflects the transmitted energy

46. Check of Understanding What is the purpose of a timebase generator in a radar installation? Synchronises the T/R Switch Provides a reference signal for the receiver unit Used to launch the pulses and collect them on return Provides a reference signal to start the transmit sequence

47. Check of Understanding A radar using doppler effect calculates the targets velocity by measuring what? Pulse return time Change of position Return pulse length Frequency shift

48. Check of Understanding Which of these statements applies to an SSR receiver? Multiband Wide bandwidth Narrow bandwidth Single frequency

49. Check of Understanding In this diagram What does the block ‘U’ represent? Timebase Generator CRT Indicator Rx Unit Tx Unit

50. Check of Understanding In SSR usage, what does the code 7700 mean? SOS Highjack Height Loss of radio Communication