Advanced Radioand Radar

Part 7Types of Radar

Introduction

We have already looked at

the general principle of operation

of both radio communication and radar.

We will now look more closely

at a variety of different types of equipment

used in the RAF,

to see how and where they are used.

Precision Approach Radar (PAR)

The purpose of PAR

is to plot the approach of an aircraft

and allow ATC to give accurate guidance

to achieve a safe landing.

The system can be used

in poor weather conditions (i.e. low cloud, limited visibility),

thus reducing interruptions

to a station’s flying programme.

PAR consists of a Radar Head cabin connected to the ATCC.

The Radar Head can rotate around a central point, so it can serve whichever runway is in use.

The Radar Head itself has three distinct assemblies;

The Radar Cabin,The Azimuth Antenna,The Elevation Antenna.

Precision Approach Radar (PAR)

Narrow beams are transmitted from each antenna.

One horizontal (2° wide by 0.5° high) for height,the other vertical (0.5° wide by 2° high) for bearing.

Precision Approach Radar (PAR)

Height

Bearing

Controlled by the ATC the beams are interlocked, and allows the aircraft to be

"captured" in the beam pattern.

Precision Approach Radar (PAR)The cross beam information is shown

on a screen with two displays.

One display is of the elevation scan, the other shows the azimuth scan.

Using both displays the controller is able to guide the aircraft

down a safe "glide path" to approach the runwayon the correct course.

Elevation

Azimuth

Instrument Landing System (ILS)ILS is a runway guidance system

for a safe landing without a ground controllerand provides the pilot with:

a. A visual indication of the aircraft’s azimuth.(on a cockpit instrument)

b. A visual indication of the aircraft’s elevation.(on the same cockpit instrument)

c. Both an audio and visual indication of the aircraft’s distance from touch down.

d. An audio indication of the identity of the airfield(in Morse code),

to confirm landing at the right airfield.

Instrument Landing System (ILS)This system has 3 separate elements:

a. Localiser Transmitter.

b. Glide Path Transmitter.

c. Outer, Middle & Inner Marker Beacons.

RUNWAY LTOM MM

GT

IM

Provides Azimuth to keep the aircraft on a central approach line.To give the pilot

elevation information.

Aircraft Passes Outer Marker (5 miles out)

Glide Path Beams Emitted

Passes Middle Marker (¾ mile out)

RUNWAY LTOM MM

GT

RUNWAY LTOM MM

GT

Instrument Landing System (ILS)

To use the ILS a pilot must position the aircraft in line with the instrument runway at a range of some 20 to 25 miles.

Instrument Landing System (ILS)The pilot has a 2-point meter.

One gives the lateral direction to fly (left or right), the other gives the vertical direction (up or down).

When the two pointers cross in the centrethe pilot is on the correct glide-path and heading.

The instrument also has warning flags which remain "set" until there is sufficientsignal strength for the system to operate.

Flags Set Signed strength Low

Instrument Landing System (ILS)

Flags Set Signed strength Low

RUNWAY LT

90 Hz

150 Hz

The airfield Localiser Transmitter (LT) radiates two beams,

one at 90 Hz, the other at 150 Hz.

If the aircraft is ‘off’ course to the left, 90 Hz is dominant and the azimuth pointer

moves to the right.

If the aircraft is ‘off’ course to the right,150 Hz is dominant and the pointer moves left.

Instrument Landing System (ILS)

Above Glide-pathBelow Glide-pathOn Glide-path

Flags Retracted Signed strength OK

GTOM MM

90 Hz

150 Hz

RUNWAY

The glide path transmitter sends out 2 beamsmodulated at 90 Hz and 150 Hz

If the aircraft is ‘too high’ on approach, 90 Hz is dominant and the lateral pointer

moves downwards.

If the aircraft is ‘too low’ on approach,150 Hz dominates and the pointer moves upwards.

Digital Resolution Direction FindingGround-based DRDF equipment provides

a direction fix for aircraft, or as an auto-triangulation system.

DRDF provides the controller with information onaircraft bearings in the following forms:

a. Digital pulses to give a digital read-out and a vector display.

b. Direct Current (DC) voltage proportional to the angle of the bearing.

c. Combined pulses from other installationsto triangulate the aircraft’s position.

Digital Resolution Direction Finding

DRDF is used primarily for aircraft in distress,by accurately pinpointing an aircraft.

The ‘distressed’ aircraft transmits a code used to determine a directional bearing of the aircraft.

Using similar information from other installations, the aircraft’s position is triangulated.

There are two control centres in the UK, one at West Drayton and the other at Prestwick.

Check of UnderstandingWhat are the distinct elements of

a PAR assembly?

Radar cabin, Elevation antennaand Range finder

Radar cabin, Range scanner and Azimuth antenna

Radar cabin, Elevation antenna and Range finder

Radar cabin, Elevation antennaand Azimuth antenna

Check of Understanding

What does PAR stand for?

Primary aircraft radar

Pin-point approach radar

Portable aircraft radar

Precision approach radar

Distance

Elevation

Azimuth

Range

Check of UnderstandingWhat does this screen portray on PAR?

Check of UnderstandingWhat does ILS stand for?

Interim Landing System

Immediate Landing System

Indicator Lights System

Instrument Landing System

Far, Middle and Runway

First, Middle and Final

Outer, Middle and Inner

Distant, Middle and Inner

Check of UnderstandingWhat are the marker beacons in an ILS?

At 1 nautical mile only

Within 25 nautical miles

Under 5 nautical miles only

Over 50 nautical miles

Check of UnderstandingAt what distance could a pilot use ILS?

In this diagram, what state is displayed?

Check of Understanding

Flags set – signal strength high

Flags retracted – signal strength high

Flags set – signal strength high

Flags retracted – signal strength low

Runway bearing number

Azimuth approach angle

Azimuth descent angle

Height to touchdown

Check of UnderstandingWhich of the following

is information supplied to a pilot from ILS?

In this diagram what action should the pilot take?

Gain height

Move left

Lose height

Move right

Check of Understanding

Which three elements make up ILS?

Marker Beacons, Glide-path Transmitter

and Localiser Transmitter

Marker Buoys, Azimuth Antenna

and Localiser Transmitter

Marker Beacons, Azimuth Antenna

and Localiser Transmitter

Marker Buoys, Glide-path Transmitter

and Localiser Transmitter

Check of Understanding

In an aircraft using ILS the meter’s flags are set because . . .

The aircraft is not on beam

The meter needs re-calibration

Signal strength is adequate

Check of Understanding

Signal strength is inadequate

Direct Radar Direction Finding.

Digital Resolution Direction Finding.

Digital Radar Direction Finding.

Direct Resolution Direction Finding.

Check of UnderstandingWhat does DRDF stand for?

Check of UnderstandingDRDF provides the controller with data

in three forms, digital pulses, a DC voltage and which other?

A sinusoidal output

An AC voltage

A sawtooth waveform

Combined digital pulses

Advanced Radioand Radar

End of Presentation