Air Traffic Systems

SECONDARY SURVEILLANCE RADAR

INTRODUCTION

AND

BASIC PRINCIPLES

Air Traffic Systems

Radar PictureTiming

&Control

Transmitter Pulses

TXRX

& PROCESSING

Received Signal

Basic Primary Radar

DISADVANTAGES OF PRIMARY RADAR

High Power

Clutter

Permanent Echo's

Weather i.e. Rain etc.

Identification

Radar PictureTiming

&Control

TXRX

& PROCESSING

Basic Secondary Radar

SSRTx 1030 MHz

Rx 1090 MHz

123ABC

Decoder Secondary returns

Military A/C Ident - Mode 1 3µs

Military Mission Ident - Mode 2 5 µs

Joint Military & Civil A/C Ident - Mode 3/A 8 µs

Civil A/C Ident - Mode B 17 µs

Altitude Data - Mode C 21 µs

Modes and Pulse Spacing

SSR Questions (Modes)

Who are you ? (Mode 1 and 3/A)

What is your altitude ? (Mode C)

What is your mission number ? (Mode 2)

Are you FRIEND or FOE ? (Mode 4)

Mode Interlacing

The ability of the system to automatically

change modes.

This enables more diverse information to

be gathered.

Military transponderset to :-Mode 1, code = 1100Mode 3/A, code = 4170Mode C, code = h1

Civil transponderset to :-Mode 3/A, code = 2210Mode C, code = h2

Military

Civil No 2210 h2 No 2210 h2 No 2210 h2

1100 4170 h1 1100 4170 h1 1100 4170 h1

CodedReplies

1 3/A C 1 3/A C 1 3/A C

Mode interlace pattern 1, 3A, C

MODE INTERLACINGMODE INTERLACING

h1 h2

EMERGENCY REPLIESCIVILIAN EMERGENCYCIVILIAN EMERGENCY

GENERAL EMERGENCY - 7700

RADIO FAILURE - 7600

HI-JACK - 7500

ADVANTAGES OF SSROVER PRIMARY RADAR

POSITIVE IDENTIFICATION

CLUTTER ELIMINATION

LOWER POWER FOR EQUIVALENT RANGE

ACCURATE HEIGHT INFORMATION

EMERGENCY INFORMATION

DISADVANTAGES OF SSR

INTERROGATIONS VIA SIDE LOBES

FALSE REPLIES UNCORRELATED IN TIME

(FRUIT)

GARBLING

TRACK WANDER

200 Miles

80 miles

Aircraft A

Aircraft C

Aircraft B

200 Miles

80 miles

Aircraft A

Aircraft B

P1 P2P2 P3

2 s

INTERROGATION SIDE LOBE SUPPRESSION

Aircraft C

Site APRF 250Hz

Site BPRF 260Hz

unwanted replies

F.R.U.I.T.

Interrogation

FRUIT

Correct reply

De-fruited video O/P

DEFRUITER PRINCIPLE

1 PRF DELAY CoincidenceGate

(Frame pulses + 2 information..)

First PRPReplies

Second PRPReplies

GARBLEGARBLE

A4 B2 D2 D4 F2

A2C2 C4F1

End of pulse

train from aircraft A

Beginning ofpulse train fromaircraft B

Overlapping repliesOVERLAPPING

TRACK WANDER1st

sweep

2nd

sweep

3rd

sweep

4th

sweep

TRACK WANDER1st

sweep

2nd

sweep

sweep

sweep

track

THE MONOPULSE SYSTEM

ELIMINATES TRACK WANDER

BECAUSE ONLY ONE PULSE

FROM A REPLY TRAIN IS NEEDED

TO OBTAIN AN ACCURATE BEARING.

BO

RE

S

IGH

T

COMBINED SUM & DIFFERENCE PATTERNS

Mono-pulse Secondary

Surveillance Radar

MSSR

Cardion Secondary Surveillance Radar

Antenna mounted on Tactical Watchman

Mounted on T101 Air Defence Radar

AIRTRAFFICCONTROL

CIVIL AIRCRAFTMILITARY AIRCRAFT

MARITIME AIRCRAFT

NAVAL SYSTEMS

MISSILE

SSR SYSTEM APPLICATIONS

This is my discrete address

MODE S

Bit 1 Bit 2 Bit 3 Bit 4

1 0 1 1 1 10 0 0 0

Bit NPreamble 8.0 s

I am able to reply to your “ALL CALL”

because I have Mode S

Data block 56 s or 112 s

0.5 s0.5 s

The future of SSR

Mode S – becoming compulsory under EASA rules

CSSR and MSSR don’t support Mode S

Airfield layout

Any Questions

?