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

Advanced Radioand Radar

Part 5Radar

IntroductionAs 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

RAdio Detection And Ranging(RADAR).

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 bearingradar can also find another vital fact

about a target aircraft –

Introduction

its height.

Radar OperationsMany factors prevent efficient operation

of a radar system:

– Signals from radio, stars, the atmosphere.

– Man-made signals from other radartransmitters, 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 OperationsMany factors prevent efficient operation

of a radar system:

Noise

Interference

Clutter

Target Characteristics

Much of this can be reduced

by electronic techniques

Types of RadarThere 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 RadarPrimary radar systems may be found in

ground, air, ship or space platforms, and are used in roles such as:

Surveillance (including weather)Early Warning

NavigationGround Mapping (from space or aircraft)

Guidance ControlTarget Detection and TrackingTerrain Following/Avoidance

Collision Avoidance and Altitude MeasurementAir Traffic Control

Primary RadarRadars 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 radaroperates on a relatively low frequency (UHF)

while a weapons system fire control radarwill operate at a very high frequency (SHF)

Primary 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

Pulse-Modulated Radar

Primary 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 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 Time1 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


• 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

SqueezeStretch

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.

SqueezeStretch

Primary Radar

The Doppler Effect

Primary RadarContinuous Wave Radar (CW)

There are two basic types of CW radar.

Continuous Wave Doppler(CW Doppler)

and

Frequency-Modulated Continuous Wave(FMCW).


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


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.

CW Doppler

Frequency-Modulated CW Radar

is a short range measuring radarcapable 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.


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 RadarBlock diagram of a typical radar installation.

Master Timing Unit (MTU) Produces regular, timed pulses, controllingthe 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 therange of 400 MHz to 40GHz.

TXM T U

TimebaseGenerator


Transmit/Receive Switch Switches both the transmitter and receiver“ON” and “OFF”.

Aerial Used to launch the RF pulses and collectthe returns for processing.

Receiver (Rx) Collects and amplifies the returning echoesand produces video pulses to the display.

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

RXT/R

Switch

TXM T U

TimebaseGenerator

C R T Indicator


Master Timing Unit (MTU)

Timebase Generator

Transmitter (Tx)

Transmit/Receive Switch

Aerial

Receiver (Rx)

CRT (Cathode Ray Tube)

T/R Switch

TXM T U

RX

TimebaseGenerator

C R T Indicator

Secondary RadarIt 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 RadarThe 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 IdentifyB) Civil IdentifyC) Height Encoded Data

Secondary RadarIFF/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)

Direction,

Speed and Type of aircraft.(direct from aircraft’s altimeter)

Secondary RadarThe main advantages of

IFF/SSR over primary radar are:

a. 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 UnderstandingWhat does RADAR stand for?

Radio direction and ranging

Ranging and direction radio

Ranging and detection radio

Radio detection and ranging

Check of UnderstandingRadar detects a target by calculating its . . .

Height, Range and Azimuth

Bearing, Height and Size

Height, Range and Velocity

Bearing, Height and Range

Check of UnderstandingIn this diagram

What does the block ‘T’ represent?

Rx Unit

Timebase Generator

Tx Unit

Master Timing Unit

A technique for minimising clutter in a radar system is:

Reduced by electronic techniques

Increased use of the PRF

Reduction of aerial scanning speed

Increased electronic countermeasures

Check of Understanding

What is the time used in rough calculations when working in Nautical miles?

10μs

1μs

6μs


12μs

Transmits waves which vary in frequency at a controlled rate

Is designed to detect targets at the longest possible range

Receives no co-operation from the target and relies upon reflection only

Utilises the change in frequency of reflected waves

Check of UnderstandingThe definition of a primary radar is one which:


What does the block ‘Q’ represent?

Rx Unit

Timebase Generator

Tx Unit

Master Timing Unit

If a radar energy wave hits a target and returns with a frequency increase,

what effect is being used?

Pulsed Frequency

Demodulation

Frequency Modulation


Doppler

If the frequency of a reflected wave of a doppler radar decreases slightly,

What is the target doing?

Climbing towards the radar

Approaching

Descending towards the radar


Moving away

6μs

10μs

15μs

12μs

Check of UnderstandingWhat is the time unit

used in rough calculations when working in statue miles?

Tx Unit

Master Timing Unit

T/R Switch

Rx Unit


What does the block ‘S’ represent?

Check of UnderstandingThe unit in a secondary radar

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

Transmit-receive switch

Interrogator

Coding Unit

Transponder

Carrier Wave

Cyclic Wave

Continuous Wave

Inter-pulsed Wave

Check of UnderstandingWhich of the following

is a type of Primary Radar?

Speed of Target

Clutter

Height of Target

Frequency

Check of UnderstandingWhich of these factors

affects radar performance?

In this diagramWhat does the block ‘V’ represent?

CRT Indicator

Timebase Generator

Tx Unit

Rx Unit


What does SSR stand for?

Secondary surveillance radar

Single side radar

Single surveillance radar

Secondary side radar


Check of UnderstandingWhat is IFF used for?

Tells the pilot how many passengers are on board.

Alerts ATC of the direction of flight.

Tells other pilots your aircraft is airworthy.

Tells everyone you are friendly.

A pulse radar calculates the target rangeby using what?

Time between thetransmitted pulses

A pulse long enoughto reach the target

A pulse strong enough to reach the target


Time between transmission and receipt of the pulse

Tx Unit

Master Timing Unit

T/R Switch

Rx Unit


What does the block ‘R’ represent?

Check of UnderstandingSecondary Radar is defined as a system . . .

Where the target reflects the transmitted energy

Which operates when the primary radar fails

Where the target absorbs the transmitted energy

Where the target respondswith its own echo

What is the purpose of a timebase generator in a radar installation?

Used to launch the pulses and collect them on return

Synchronises the T/R Switch

Provides a reference signal for the receiver unit


Provides a reference signal to start the transmit sequence

A radar using doppler effectcalculates the targets velocity

by measuring what?

Frequency shift

Pulse return time

Return pulse length

Change of position


Which of these statements applies to an SSR receiver?

Single frequency

Multiband

Narrow bandwidth

Wide bandwidth


In this diagramWhat does the block ‘U’ represent?

CRT Indicator

Timebase Generator

Tx Unit

Rx Unit


Loss of radio Communication

SOS

Height

Highjack

Check of UnderstandingIn SSR usage,

what does the code 7700 mean?

What information is given out with Mode 3C in SSR?

Military identity

Height encoded data

Aircraft type

Civil identity


In a radar installation,what does the Master Timing Unit do?

Demodulates the frequency for the CDT display

Switches the timebase generator on and off

Produces pulses at the required level to drive the aerial


Controls the start of the transmitter and the timebase generator

Advanced Radioand Radar

End of Presentation

Documents

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