Basic Radar Theory Flashcards
RADAR stands for
Radio Detection and ranging
Principles of radar system
Sends pulses at speed of light which hit an object and pulse reflected in the form of an echo
Time taken for pulse to return used to calculate range.
Primary Radar Gives
Bearing and distance of targets
Primary ground radar is used to detect
Aircraft not equipped with secondary radar transponder
Echo returns depend on
Corners = more echoes
Size/shape big/sharp = more returns
Water = more echoes
Ice crystal = less echoes
Transmit/receive switch
Protect receiver from high powered pulses
Ensures receiver is switched off when transmitting and ensures transmitter is off when receiver is on
Operations of a radar
Antenna transmits a big pulse of energy from the amplifier
Receiver receives the returning signal at a lower energy
Received signal is amplified
Processor calculate the range by comparing time and displays on screen
Waiting period
Duration in the receive phase waiting to receive returns
Must be twice max design range
Pulse length
Duration of the pulse measured in microseconds
Transmit phase
Pulse recurrence interval
Time from the transmission of one pulse to the next pulse
Pulse repetition frequency
Number of pulses occurring in a second
1 ——— PRI
Beam width
Narrow beam ideal/more information on target
Bigger dish = narrower beam width
Shorter the range the higher the
Frequency
Larger the range the lower the
Frequency
Radar range depends on
Frequency
Height of antenna
Height of aircraft
Pulse repetition frequency
Pulse length
Power of the pulse
Aerodrome surface movement radar
SHF 10-20GHZ
+ faster rotating antenna
+ higher frequency - shorter wavelength/narrower beam
+ shorter range = shorter pulse = greater resolution in depth
Maximum unambiguous range is effected by
Pulse repetition frequency
Minimum range of radar is affected by
Pulse width
Max unambiguous range formula
Speed of light
—————————————-
2 x Pulse repetition frequency
Range (in km) = 300,000/ (PRF x 2)
Range formula with transmitter power
4 x square root of transmitter power
Minimum pulse range formula
Speed of light x pulse width
—————————————-
2
Terminal Radar (PRF and Range)
High Pulse repetition frequency
Short range
Short time between pulses
Area radar (PRF) (Range)
Low pulse repetition frequency
Relatively long range
Long time between pulses
Equation to determine distance of a radar return
Time between sending pulse/receiving echo x speed of light
———————————————————————————-
2
PSR - range and bearing is acquired
At the same time
Max and minimum range of primary radar
Max range = c/(2xPRF) (remember km)
Min Range = (c x pulse width)/2
MTI
Moving target indicator used to indicate moving targets and eliminate objects on the ground
To double the range of PSR the power output required
Increases by 16
Propagation delay
Time taken for the pulse to travel from the radar to the target and back to the radar
Formula for PRF frequency
Rearranging the range formula
PRF = 300,000/ (range km x 2)
Pulse Recurrence Rate
Rate at which pulses are emitted - Same as pulse repetition frequency
Amount of pulses transmitted per second
Minimum and maximum is limited by
Minimum - Pulse Length
Maximum - Pulse repetition frequency
ASMR
Aerodrome surface movement radar
Provides high quality display of all aircraft and vehicles and taxiways
