Advanced Radio and Radar Secondary Radar Radar Display

Advanced Radio and Radar Secondary Radar & Radar Display Lecture Four

Secondary Radar Secondary radar systems are those where the target responds with its own echo. Identification Friend or Foe (IFF) is such a method. Aircraft are fitted with a transponder which resubmits a reply signal to an interrogating transmitter/receiver. IFF equipment is specifically for military use, the civilian version is called SSR, Secondary Surveillance Radar which uses wide bandwidth receivers.

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 Mode 2 Mode 3 Military Aircraft Identify Military Mission Identify A) Common Military/Civilian Aircraft Identify B) Civil Identify C) Height Encoded Data

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 (direct from aircraft’s altimeter) Direction, Speed and Type of aircraft. The aircraft can also send emergency information such as: Loss of radio communications (code 7600) Hijack (code 7500) SOS (code 7700)

Secondary Radar The main advantages of IFF/SSR over primary radar are: a. 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.

Introduction We know a simple aerial will radiate electromagnetic waves equally in all directions; it can also receive signals from all directions. But this is of limited use when trying to determine the direction of a particular reflection.

Introduction Instead of radiating, the radio wave needs to be concentrated into a single beam so that the radar can be made to "look" and "listen" in one specific direction at a time.

Introduction To detect bearings the aerial is rotated, sweeping a narrow beam in a complete circle. (called Scanning). All reflections can be plotted around a circle – with the aerial at the centre.

Radar Display Obtaining a target is only part of the detecting process. The operator needs to "see" the target in a visual form. For this we use a Cathode Ray Tube (CRT) which works on a similar principle to a television screen. CRT

Radar Display As the time interval between the radio pulses is short the actual CRT screen can be calibrated in miles to match the range of the pulse. 12 10 10 12 CRT

Radar Display The instant the pulse is transmitted a spot travels across the CRT screen moving at a constant speed. CRT

Radar Display If a target is detected a "blip" appears. Because the screen is calibrated in miles we know the distance (range) to the target, but it cannot determine the object’s bearing, or its height. CRT

Radar Display To get the bearing and height we must make some alterations to the CRT display screen, So we shall start with the bearing – CRT

Radar Display To find the bearing of a target, we need to find its Azimuth (bearing measured from North). CRT

Radar Display By using a Plan Position Indicator (PPI) that rotates a beam through 360° the bearing of any target can be calculated. Therefore a PPI becomes a radial trace in time with the radar N W E S CRT

Radar Display It is also possible to display range and bearing by adding Range Rings to aid in range finding. N W E S CRT

Radar Display The display starts from the centre of the screen, and produces a radial trace moving in time with the rotation of the aerial, and ‘blipping’ the target contact. N W E S CRT

Radar Display To change the display range on a radar screen the velocity of the timebase sweep is changed to allow for the different range. N W E S CRT

Other Ranges Having determined both range and bearing; by using the Slant Range (distance from the radar to the target). it is possible to determine object height e g n a R t n ANCE a l S IST D Ө Height Radar Angle Height = Slant Range x sin Ө

Other Ranges Having determined both range and bearing; by using the Slant Range (distance from the radar to the target). the target’s ground range can also be calculated e g n a R t n ANCE a l S IST D Ө Height Radar Angle Ground Range DISTANCE Ground Range = Slant Range x cos Ө

Other Ranges The slant triangle is made up of Slant range, height and ground range. Height = Slant Range x sin Ө Ground Range = Slant Range x cos Ө e g n a R t n ANCE a l S IST D Ө Radar Angle Ground Range DISTANCE Height

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

Check of Understanding The unit in a secondary radar which re-transmits the signals is the: Transponder Transmitter Interrogator Transmit-receive switch

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.

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

Check of Understanding How many modes are there in IFF/SSR? One Two Three Four

Check of Understanding There are 3 modes in SSR but how many sub modes are there in Mode 3? One Two Three Four

Check of Understanding Mode B in SSR gives out what information? Height encoded data Aircraft type Military identity Civil identity And Mode C in SSR gives out what information? Height encoded data Aircraft type Military identity Civil identity

Check of Understanding The receivers on an SSR system are: Narrow Bandwidth Multi Frequency Wide Bandwidth Single Frequency

Check of Understanding In SSR usage, what does the code 7700 mean? SOS Height Highjack Information Loss of radio Communication And what does the code 7500 mean? SOS Height Highjack Information Loss of radio Communication

Check of Understanding What do the initials CRT stand for? Cathode Ray Tube Cathode Radiation Tube Capacitor Resistance Translator Cathode Radio Tube

Check of Understanding Which of these statements applies to a PPI radar display? It uses a height finding radar It has a circular trace using radial deflection It can only display ranges It has a radial trace rotating in time with the radar

Check of Understanding What can be added to a PPI to aid in its operation? Height Indicators Sector Ranges Range Rings Bearing Rings

Check of Understanding A PPI is A radial trace in time with the target A timebase trace A radial trace in time with the radar A rotary trace

Check of Understanding To change the range display on a radar screen. . . The timebase sweep velocity is changed The transmitter power is changed A new set of markers is required The display intensity is changed

Check of Understanding What is a slant triangle composed of? Slant range, target and ground range Angle of elevation, height and target velocity Slant range, height and ground range Angle of elevation, height and ground range

Check of Understanding The ground range of a target can be calculated by using. . . Slant range x sin Slant range x tan Slant range x cos Slant range x height The height of a target can be calculated by using. . . Slant range x sin Slant range x tan Slant range x cos Slant range x height

Advanced Radio and Radar End of Presentation