Day 2 Flashcards
What are the uses of an airborne radar?
Military
Weather
Navigational aids
Explain a Radar System
Synchroniser -> Modulator -> Transmitter -> Switch (Duplexer) -> Antenna
Antenna -> Switch (Duplexer) -> Receiver -> Display -> Synchroniser
What is the purpose of a Transmitter?
Outputs a high power signal at desired frequency
What are the two types of transmission lines?
Waveguide - between transmitter, duplexer, antenna and receiver (generally above 3GHz)
Coaxial Cable - between everything else
What are the 2 basic types of Radar Transmitters?
Oscillators - Converts prime power (DC) straight into a high-power RF output
Amplifier - Produce a high-power replica of an input signal
What are the 3 main Transmitter Devices?
Magnetron (Oscillator)
Travelling Wave Tube (Amplifier)
Field Effect Transistor (Amplifier)
Within Pulse Generation, how is pulse duration and width defined?
Half power point of the pulse
What can pulse modulation change?
Amplitude
Frequency
Phase
What does the synchroniser do?
Sends a continuous stream of pulses used as timing reference
What does the Modulator do?
Used to control the PRF and shape the pulse.
Provides a high power DC signal to Transmitter
What does the Antenna do?
Shapes the beam
What are the Factors affecting Radar?
Frequency - Antenna size, Attenuation
PRF - Data rate, Maximum Unambiguous Range (MUR)
PW - Average Power, Minimum Detection Range (MDR)
Average Power - =Peak Power x Pulse Width, Range
Beamwidth - Angular Discrimination, Beam Shape, Frequency
ARP - Maximum Detection Range, Data Rate
Antenna - Size, weight, sidelobes, driving equipment, frequency
Weight - Scanner, waveguide, transmitter (power)
Why do we have a Switch/Duplexer
To switch between transmit and receive
To stop the high power signal from the transmitter overloading the receiver
What should the receive section of a Radar System do? 8 points
Accept target echoes Protect the receiver Amplify target echoes Remove unwanted echoes/signals Demodulate received RF Carry out signal processing Convert RF signals into video pulses Display Pulses
Breakdown of a receiver?
Protection Circuits Amplify signal Remove clutter Demodulate Signal Signal Processing Detector creates video Pulses
How does a radar know how far away to put the contact from the aircraft?
Range is calculated as time taken for pulse to travel to target and return divided by 2.
Therefore we need a Synchroniser to provide a time reference
What are the types of radar display?
Plan Position Indicator (PPI)
B-scope
A-scope
Explain a PPI Display
Bird’s eyes view
Oriented to North (SA) or Aircraft Bearing (Weather or Avoidance)
Radar Antenna represented in the centre of the display
Distance from it and height above ground is drawn as concentric circles
As the radar antenna rotates, a radial trace on the PPI sweeps in unison with it
Explain a B-scope display
Plots signals in a rectangular area with higher resolution than PPI
Azimuth going from left to right
Range from bottom to top
Side closest to aircraft on bottom
Explain a A-scope display
Plots amplitude of a signal against range (or time) to give a high resolution display
What target information can we get from contact on a radar and how?
Range - Speed of light x time taken divided by 2
Bearing - Linked to scanner position
Height - V Beams, stacked feeds, nodding fan
Course - Draw a line between successive plots
Speed - Calculate distance/time between plots
Shape/size/outline - A scope / PPI contact size / Brightness
What are the Optimisation Techniques available?
Automatic gain control Constant false alarm rate Range gain 2nd time round returns Change of: PRF, PW, Peak power, ARP & mode Pulse compression
What functions do ES receivers perform?
Threat warning
Tactical systems
Strategic systems
Go through ES Receivers table
Criteria for an ES receiver ( 11 points)
Sensitive 100% intercept probability Covers wide range of frequencies Coverage (360 in azimuth & relevant elevation angles) Accurate and immediate direction finding Measures parameters Can deal with different types of radars De-interleave signals Identify emitter and prioritise Display results clearly Provide audio alarm as necessary
Components of an ES receiver
Antenna –> Amps –> Receivers –> Processor –> Outputs
Receivers –> DOA (direction of arrival) Resolver –> Outputs
What is deinterleaving
Automatic sorting of incoming radar signals
E.g sorted by frequency, PRF/PRI
What does an ES receiver do?
De-interleaves pulse train
Provides parametric measurements
What does an ES processor do?
Uses mission dependent data to identify emitters using parameters
What does an ES DoA resolver do
Provides bearing information using amplitutde or phase comparison
What is unintentional pulse modulation?
Specific emitter identification
Can be dependent on damage, installation of components or user utilisation.
What is bandwidth?
The difference between the upper frequencies in a continuous set of frequencies measured in Hz.
What factors will affect signal quality? (SNR)
Distance from source
Atmospheric conditions
No LOS
Jamming
