Week 2 Theory Flashcards
What is frequency diveristy
When a radar transmits 2 or more frequencies simultaneously
What is frequency agility
When a radar switches between multiple frequencies in a controlled manner
Benifits of frequency agility
Good anti clutter
Eliminates second time round returns
Different material reflect different frequencies better than others
Benefits of continuous wave
Good for doppler
High average power
Narrow bandwidth
Disadvantages of continuous wave
Cant calculate range
Separate transmitter and receiver needed
What is frequency modulated continuous wave (FMCW)
Radar transmits continuously but changes freq over time
What is Interrupted continuous wave (ICW)
CW signal that gets interrupted not stopped so that the phase of the signal remains coherent
Types of inter pulse modulation
Stagger
Dwell and switch
Jitter
Agility
Types of stagger
Simple- seven or less
Complex- more than seven
What is switch and dwell
PRI is set for a number of pulses and then switches to a different freq for a number of pulses
Types of jitter
Discrete
Random
Firing order def
Order in which PRIs are transmitted
Element def
Describes an individual PRI
Positions def
Total number of PRIs in a cycle
Cycle length def
Time it takes to go through 1 sequence
Cycle rate def
Number of times a sequence is repeated in a second
Mean PRI def
Average of all positions in a cycle
What is UMOP
Unintentional modulation on pulse
Knows as SEI or fingerprinting
What is FMOP
Frequency modulation on pulse
What is FMOP used for
Varying frequency over the pulses length (sweep) allows for better range resolution
What is doppler
Apparent shift in frequency as an object moves towards or away from and observer
What is coherence
Continuity of phase from one signal to the next
What is doppler notch
When the velocity of a contact is bellow which a radar classes them as clutter and does not identify them
Tangental fade
Reducing of doppler due to a reduction in radial velocity
What is a pulse doppler range vs velocity
Range ambiguous (blind range) Velocity unambiguous
What is an MTI radars range vs velocity
Range unambiguous Velocity ambiguous (blind speed)
How does blind speed occur
When target is stationary
Or
Target has moved a whole number of wavelengths between pulses
How is blind speed solved
Raise PRF
Inter pulse modulation-if one freq misses another will hit
When does blind speeds occur
When doppler shift is equal to PRF or its harmonics
How are blind ranges resolved
Inter pulse modulation
Electrical components of a radar system
Oscillator
Mixer
Filter
Attenuator
Types of orbit
Circular
Eliptical
Whats is the apogee
Max height min speed
What is the perigee
Min height max speed
Ad and dis of low earth orbit
Can be fixed
Decreased lag time
Need many satellites for full coverage
Ad and dis of geostationary/geosychronus
Infinite dwell time
Doesn’t require a following antenna
High cost
Impossible to repair
Ad and dis of sub synchronus
Fast coverage of large areas (up to 12 hour orbit)
Need many satellites for full coverage
What is SEAD
Suppression of enemy air defence
Neutralise or degrade enemy defence
Enemies capability will remain
What is DEAD
Destruction of enemy air defence
Permanently removes enemies capability
Destruction of a threat is generally preferable
Triad of SEAD
C-130 compass call
EA-18 Growler
Anti radiation missiles
What is a time sensitive target
Target that requires an immediate response
What is the missile engagement process
Search Aquire Track Launch Intercept
What radar is used in the acquire phase
TA
What radar is used in the track phase
TT
What radar is used in the launch phase
TI
MG
fC
Types of homing missile
Passive
Semi active
Active
How does semi active missile work
Missile homes passively
Target is illuminated by launch platform
How does passive missile work
Missile homes into transmissions emitted bu the target
Eg IR, RF, UV
How does active missile work
Missile transmits and receives
Fire and forget
What is command line of sight (CLOS)
Target and missile are tracked
Data link command one way to missile from ground station
Follows target
What is command off line of sight
Target and missile are illuminated
Data link one way to missile
Target is intercepted
What is track via missile
Target and missile are tracked
Missile also tracks target
Two way data link between missile and ground
Properties of a Radar Warning Receiver (RWR)
Sensitive 100% intercept Covers wide range of freqs 360° azimuth Accurate De interleave signals Display
Types of RWR
Crystal video receiver (CVR)
Instantaneous frequency measurement receiver (IFM)
Superheterodyne receiver
Properties of CVR
Covers a wide bandwidth
Simple and cheap
Cannot measure freqs
Cannot detect CW
Properties of a IFM
Measures freqs
Simple
Cannot measure PRF or PW
Properties of a SuperHet
Very sensitive and selective
Phase preserved so measures doppler
Needs to be programmed
Reliant on software to know what to look for
What is MDD
Mission dependant data
Library of emitter parameters, scan strategies, maps etc
Def of a countermeasure
Any action taken to negate a threat
What are the three types of jamming
Spot
Barrage
Sweep
What is radar burnthrough
As you get closer to the radar you are jamming returns get stronger and you are seen
What is electronic repeater jamming
Takes a signal and sends it out with a time delay
What is false target generation
Time delay retransmits position forward and back
Retransmit into side-lobes to change position left and right
Types of active decoys
Towed radar decoy
Expendable active decoy
Types of passive decoy
Chaff
Cut to half wavelength of the signal you want to jam
How to create stealth
Reduction of radar cross section
Reflectivity of materials
Shape-lumps bumps and cavities
What does a missile warning system (MWS) detect
Radar cross section and movement
Mussel flash
Motor ignition
Motor plume
Types of MWS
Radar MWS
IR MWS
UV MWS
Laser MWS
Properties of a flare
High peak intensity
Fast rise time
Long burn time
Credible signature
How to counter a dual band detector
Spectral flares
How to counter kinematic flare rejection
Aerodynamic flares
What is an IRCM
Multi directional IR jammer
What is a DiRCM
Focuses energy in a beam for better range and to blind the missile
What does a low probability of intercept (LPI) radar do
Reduces possibility of an enemy spotting a radar
3 types of LPI radar
LPID-low prob of identification
LPI- low prob of intercept
Quiet radar
Properties of Secondary surveillance radar
Greater range
Less power needed
Coded info
Requires aircraft to have transponder to interrogate
What is fruiting
False replies unsynchronised in time
SSR transmit and receive on same freq so could get unwanted reply
What is garbling
When two aircraft are similar in range and/or azimuth within 3.2nm, signal gets mixed up
