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Advanced Radio and Radar. Part 5 Radar. Introduction. As World War II approached, scientists and the military were keen to find a method of detecting aircraft outside the normal range of eyes and ears. They found one, and at first called it Radio Detection Finding (RDF),

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introduction
Introduction

As World War II approached,

scientists and the military were keen to find

a method of detecting aircraft

outside the normal range of eyes and ears.

They found one,

and at first called it

Radio Detection Finding (RDF),

then changed it to

RAdioDetection And Ranging

(RADAR).

introduction1
Introduction

Radar fires powerful radio waves

towards a target,

and collects the reflected energy.

Radar operators find the position of the target

in terms of range & bearing.

As well as range and bearing

radar can also find another vital fact

about a target aircraft –

its height.

radar operations
Radar Operations

Many factors prevent efficient operation

of a radar system:

– Signals from radio, stars, the atmosphere.

– Man-made signals from other radar

transmitters, electrical apparatus and machinery.

– Echoes from hills, buildings, sea, clouds,

hail, rain and snow.

– Shape and composition

have an effect on its echo.

Noise

Interference

Clutter

Target Characteristics

radar operations1
Radar Operations

Many factors prevent efficient operation

of a radar system:

Noise

Much of this

can be reduced

by electronic techniques

Interference

Clutter

Target Characteristics

types of radar
Types of Radar

There are basically two different types of radar,

Primary and Secondary.

Primary Radar relies solely on the energy

that it has generated and radiated,

being reflected back from the target –

i.e. an echo.

Secondary Radar

has some co-operation from the target –

the target generates its own ‘em’ radiation.

primary radar
Primary Radar

Primary radar systems may be found in

ground, air, ship or space platforms,

and are used in roles such as:

Surveillance (including weather)

Early Warning

Navigation

Ground Mapping (from space or aircraft)

Guidance Control

Target Detection and Tracking

Terrain Following/Avoidance

Collision Avoidance and Altitude Measurement

Air Traffic Control

primary radar1
Primary Radar

Radars operate in 2 different modes:

Pulse-Modulated Radar (pulsed)

and Continuous Wave Radar (CW).

They operate in the Ultra High Frequency (UHF)

or Super High Frequency (SHF) bands.

This frequency depends on the radar function –

Long range search radar

operates on a relatively low frequency (UHF)

while a weapons system fire control radar

will operate at a very high frequency (SHF)

primary radar2
Primary Radar

Pulse-Modulated Radar

A pulsed radar uses an echo principle.

The transmitter fires a pulse of energy

and then "listens" for an echo to return.

The pulses are transmitted at a rate

which determines the range of the radar.

This is called the

Pulse Repetition Frequency (PRF).

Fires pulse

‘Listens’

Return Echo

primary radar3
Primary Radar

Pulse-Modulated Radar

PRF ranges from 250pps for long-range radars

to 2000pps for short-range radars.

For long-range radar,

1 million watts (megawatt) of (RF) power

is required.

This power is used only during the brief

transmission of the pulse.

The transmitter then ‘rests’ until the next pulse,

and the receiver ‘listens’ for an echo.

Fires pulse ‘listens’ Fires pulse

primary radar4
Primary Radar

Pulse-Modulated Radar

To calculate the distance to the target,

the time for a pulse to travel one mile and return

is known as a "Radar Mile“.

Target Range Range Return Echo Time

1 Kilometre 1000 m 6.67 ms (6μs)

1 Statute Mile 5280 ft 10.75 ms (10μs)

1 Nautical Mile 6080 ft 12.36 ms (12μs)

So if we measure the elapsed time between

the transmission and reception of a pulse,

we can use the formula:

Distance = Speed x Time

primary radar5
Primary Radar

The Doppler Effect

  • Relative movement of a sound source
  • towards and away from a fixed point
  • causes frequency modulation in the sound wave.
  • This is a natural phenomenon

Stretch

Squeeze

primary radar6
Primary Radar

The Doppler Effect

  • A radio transmission from an aircraft
  • would be affected in exactly the same way.
  • This is called the Doppler Effect.

Stretch

Squeeze

primary radar7
Primary Radar

Continuous Wave Radar (CW)

There are two basic types of CW radar.

Continuous Wave Doppler

(CW Doppler)

and

Frequency-Modulated Continuous Wave

(FMCW).

primary radar8
Primary Radar

Continuous Wave Radar (CW)

When the radar sends out a pulse,

if the target is moving towards the transmitter

the reflected waves become bunched up.

(i.e. they acquire a higher frequency)

(and vice versa if the target is moving away).

(i.e. they acquire a lower frequency)

CW Doppler

primary radar9
Primary Radar

Continuous Wave Radar (CW)

CW Doppler

The radar equipment is able to detect

these small changes in frequency shifts

and so determine the target’s velocity

(speed and direction)

with respect to the transmitter.

A similar system is used by traffic police

with their "speed gun".

This is called the Doppler Effect.

primary radar10
Primary Radar

Continuous Wave Radar (CW)

Frequency-Modulated CW Radar

is a short range measuring radar

capable of determining distance.

It is often used as a “radar altimeter”

to measure the exact height

during the landing procedure of aircraft,

and as early-warning radar,

and proximity sensors.

primary radar11
Primary Radar

Continuous Wave Radar (CW)

Frequency-Modulated CW Radar

The signal is transmitted over a fixed band,

and made to vary in frequency

in a controlled cyclic manner with respect to time.

By measuring the frequency of the returning echo

it is possible to calculate the time interval elapsed

since that frequency was transmitted,

and thus the target’s range.

primary radar12
Primary Radar

Block diagram of a typical radar installation.

Master Timing Unit (MTU) Produces regular, timed pulses, controlling

the start of the timebase generator .

Timebase Generator Provides the reference signal for the start

of the transmit sequence.

Transmitter (Tx) Produces high energy RF pulses in the

range of 400 MHz to 40GHz.

M T U

TX

Timebase

Generator

primary radar13
Primary Radar

Block diagram of a typical radar installation.

Transmit/Receive Switch Switches both the transmitter and receiver

“ON” and “OFF”.

Aerial Used to launch the RF pulses and collect

the returns for processing.

Receiver (Rx) Collects and amplifies the returning echoes

and produces video pulses to the display.

CRT (Cathode Ray Tube) Displays targets to the operator.

RX

T/R Switch

C R T Indicator

M T U

TX

Timebase

Generator

primary radar14
Primary Radar

Block diagram of a typical radar installation.

Master Timing Unit (MTU)

Timebase Generator

Transmitter (Tx)

Transmit/Receive Switch

Aerial

Receiver (Rx)

CRT (Cathode Ray Tube)

RX

T/R Switch

C R T Indicator

M T U

TX

Timebase

Generator

secondary radar
Secondary Radar

It is vital to know the identity of aircraft

displayed on an air traffic controller’s screen.

Identification Friend or Foe (IFF)

is such a method.

Aircraft are fitted with a transmitter/receiver

(transponder)

which resubmits a reply signal to

an interrogating transmitter/receiver

(interrogator).

IFF equipment is specifically for military use,

the civilian version is called SSR,

Secondary Surveillance Radar

secondary radar1
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 Military Aircraft Identify

Mode 2 Military Mission Identify

Mode 3 A) Common Military/Civilian Aircraft Identify

B) Civil Identify

C) Height Encoded Data

secondary radar2
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

The aircraft can also send

emergency information such as:

Loss of radio communications (code 7600)

Hijack (code 7500)

SOS (code 7700)

(direct from aircraft’s altimeter)

Direction,

Speed

and Type of aircraft.

secondary radar3
Secondary Radar

The main advantages of

IFF/SSR over primary radar are:

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.

check of understanding
Check of Understanding

What does RADAR stand for?

Ranging and direction radio

Radio detection and ranging

Ranging and detection radio

Radio direction and ranging

check of understanding1
Check of Understanding

Radar detects a target by calculating its . . .

Bearing, Height and Size

Bearing, Height and Range

Height, Range and Velocity

Height, Range and Azimuth

slide28

Check of Understanding

In this diagram

What does the block ‘T’ represent?

Timebase Generator

Rx Unit

Master Timing Unit

Tx Unit

slide29

Check of Understanding

A technique for minimising

clutter in a radar system is:

Increased use of the PRF

Increased electronic countermeasures

Reduction of aerial scanning speed

Reduced by electronic techniques

slide30

Check of Understanding

What is the time used in rough calculations

when working in Nautical miles?

1μs

6μs

10μs

12μs

slide31

Check of Understanding

The definition of a primary radar is one which:

Is designed to detect targets

at the longest possible range

Utilises the change in frequency of reflected waves

Receives no co-operation from the target

and relies upon reflection only

Transmits waves which vary in frequency

at a controlled rate

slide32

Check of Understanding

In this diagram

What does the block ‘Q’ represent?

Timebase Generator

Rx Unit

Master Timing Unit

Tx Unit

slide33

Check of Understanding

If a radar energy wave hits a target

and returns with a frequency increase,

what effect is being used?

Demodulation

Frequency Modulation

Pulsed Frequency

Doppler

slide34

Check of Understanding

If the frequency of a reflected wave

of a doppler radar decreases slightly,

What is the target doing?

Approaching

Climbing towards the radar

Moving away

Descending towards the radar

slide35

Check of Understanding

What is the time unit

used in rough calculations

when working in statue miles?

10μs

12μs

15μs

6μs

slide36

Check of Understanding

In this diagram

What does the block ‘S’ represent?

Master Timing Unit

Rx Unit

T/R Switch

Tx Unit

check of understanding2
Check of Understanding

The unit in a secondary radar

which re-transmits the signals is called the . . .

Interrogator

Transponder

Coding Unit

Transmit-receive switch

slide38

Check of Understanding

Which of the following

is a type of Primary Radar?

Cyclic Wave

Inter-pulsed Wave

Continuous Wave

Carrier Wave

slide39

Check of Understanding

Which of these factors

affects radar performance?

Clutter

Frequency

Height of Target

Speed of Target

slide40

Check of Understanding

In this diagram

What does the block ‘V’ represent?

Timebase Generator

CRT Indicator

Rx Unit

Tx Unit

slide41

Check of Understanding

What does SSR stand for?

Single side radar

Secondary side radar

Single surveillance radar

Secondary surveillance radar

check of understanding3
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.

slide43

Check of Understanding

A pulse radar calculates the target range

by using what?

A pulse long enough

to reach the target

Time between transmission

and receipt of the pulse

A pulse strong enough

to reach the target

Time between the

transmitted pulses

slide44

Check of Understanding

In this diagram

What does the block ‘R’ represent?

Master Timing Unit

Rx Unit

T/R Switch

Tx Unit

check of understanding4
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

slide46

Check of Understanding

What is the purpose of

a timebase generator in a radar installation?

Synchronises the T/R Switch

Provides a reference signal for the receiver unit

Used to launch the pulses and collect them on return

Provides a reference signal to start the transmit sequence

slide47

Check of Understanding

A radar using doppler effect

calculates the targets velocity

by measuring what?

Pulse return time

Change of position

Return pulse length

Frequency shift

slide48

Check of Understanding

Which of these statements

applies to an SSR receiver?

Multiband

Wide bandwidth

Narrow bandwidth

Single frequency

slide49

Check of Understanding

In this diagram

What does the block ‘U’ represent?

Timebase Generator

CRT Indicator

Rx Unit

Tx Unit

slide50

Check of Understanding

In SSR usage,

what does the code 7700 mean?

SOS

Highjack

Height

Loss of radio Communication

slide51

Check of Understanding

What information is given out

with Mode 3C in SSR?

Height encoded data

Military identity

Civil identity

Aircraft type

slide52

Check of Understanding

In a radar installation,

what does the Master Timing Unit do?

Switches the timebase generator

on and off

Demodulates the frequency

for the CDT display

Controls the start of the transmitter and the timebase generator

Produces pulses at the

required level to drive the aerial

advanced radio and radar1

Advanced Radioand Radar

End of Presentation