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
?