Day 2

Question 1

What are the uses of an airborne radar?

Answer 1

Military
Weather
Navigational aids

Question 2

Explain a Radar System

Answer 2

Synchroniser -> Modulator -> Transmitter -> Switch (Duplexer) -> Antenna
Antenna -> Switch (Duplexer) -> Receiver -> Display -> Synchroniser

Question 3

What is the purpose of a Transmitter?

Answer 3

Outputs a high power signal at desired frequency

Question 4

What are the two types of transmission lines?

Answer 4

Waveguide - between transmitter, duplexer, antenna and receiver (generally above 3GHz)
Coaxial Cable - between everything else

Question 5

What are the 2 basic types of Radar Transmitters?

Answer 5

Oscillators - Converts prime power (DC) straight into a high-power RF output

Amplifier - Produce a high-power replica of an input signal

Question 6

What are the 3 main Transmitter Devices?

Answer 6

Magnetron (Oscillator)
Travelling Wave Tube (Amplifier)
Field Effect Transistor (Amplifier)

Question 7

Within Pulse Generation, how is pulse duration and width defined?

Answer 7

Half power point of the pulse

Question 8

What can pulse modulation change?

Answer 8

Amplitude
Frequency
Phase

Question 9

What does the synchroniser do?

Answer 9

Sends a continuous stream of pulses used as timing reference

Question 10

What does the Modulator do?

Answer 10

Used to control the PRF and shape the pulse.

Provides a high power DC signal to Transmitter

Question 11

What does the Antenna do?

Answer 11

Shapes the beam

Question 12

What are the Factors affecting Radar?

Answer 12

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)

Question 13

Why do we have a Switch/Duplexer

Answer 13

To switch between transmit and receive

To stop the high power signal from the transmitter overloading the receiver

Question 14

What should the receive section of a Radar System do? 8 points

Answer 14

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

Question 15

Breakdown of a receiver?

Answer 15

Protection Circuits
Amplify signal
Remove clutter
Demodulate Signal
Signal Processing
Detector creates video Pulses

Question 16

How does a radar know how far away to put the contact from the aircraft?

Answer 16

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

Question 17

What are the types of radar display?

Answer 17

Plan Position Indicator (PPI)
B-scope
A-scope

Question 18

Explain a PPI Display

Answer 18

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

Question 19

Explain a B-scope display

Answer 19

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

Question 20

Explain a A-scope display

Answer 20

Plots amplitude of a signal against range (or time) to give a high resolution display

Question 21

What target information can we get from contact on a radar and how?

Answer 21

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

Question 22

What are the Optimisation Techniques available?

Answer 22

Automatic gain control
Constant false alarm rate
Range gain
2nd time round returns
Change of: PRF, PW, Peak power, ARP & mode
Pulse compression

Question 23

What functions do ES receivers perform?

Answer 23

Threat warning

Tactical systems

Strategic systems

Question 24

Go through ES Receivers table

Question 25

Criteria for an ES receiver ( 11 points)

Answer 25

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

Question 26

Components of an ES receiver

Answer 26

Antenna –> Amps –> Receivers –> Processor –> Outputs

Receivers –> DOA (direction of arrival) Resolver –> Outputs

Question 27

What is deinterleaving

Answer 27

Automatic sorting of incoming radar signals

E.g sorted by frequency, PRF/PRI

Question 28

What does an ES receiver do?

Answer 28

De-interleaves pulse train

Provides parametric measurements

Question 29

What does an ES processor do?

Answer 29

Uses mission dependent data to identify emitters using parameters

Question 30

What does an ES DoA resolver do

Answer 30

Provides bearing information using amplitutde or phase comparison

Question 31

What is unintentional pulse modulation?

Answer 31

Specific emitter identification

Can be dependent on damage, installation of components or user utilisation.

Question 32

What is bandwidth?

Answer 32

The difference between the upper frequencies in a continuous set of frequencies measured in Hz.

Question 33

What factors will affect signal quality? (SNR)

Answer 33

Distance from source
Atmospheric conditions
No LOS
Jamming