Air Traffic Systems Air Traffic Systems SECONDARY SURVEILLANCE

Air Traffic Systems

Air Traffic Systems SECONDARY SURVEILLANCE RADAR INTRODUCTION AND BASIC PRINCIPLES

Basic Primary Radar Transmitter Pulses TX Timing & Control RX & PROCESSING Received Signal Radar Picture

DISADVANTAGES OF PRIMARY RADAR § High Power § Clutter Permanent Echo's Weather i. e. Rain etc. § Identification

Basic Secondary Radar Tx 1030 MHz SSR Rx 1090 MHz RX TX & PROCESSING Timing & Control Decoder Secondary returns 123 ABC Radar Picture

Modes and Pulse Spacing 3µs Military A/C Ident - Mode 1 5 µs Military Mission Ident - Mode 2 8 µs Joint Military & Civil A/C Ident - Mode 3/A Civil A/C Ident - Mode B Altitude Data - Mode C 17 µs 21 µs

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.

MODE INTERLACING Military transponder set to : Mode 1, code = 1100 Mode 3/A, code = 4170 Mode C, code = h 1 Civil transponder set to : Mode 3/A, code = 2210 Mode C, code = h 2 h 1 Mode interlace pattern 1, 3 A, C 3/A C 2210 h 2 No 2210 h 2 Military 1100 4170 h 1 1 Civil Coded Replies 3/A C 1 No 2210 h 2 No 1 3/A C

EMERGENCY REPLIES CIVILIAN EMERGENCY GENERAL EMERGENCY - 7700 RADIO FAILURE - 7600 HI-JACK - 7500

ADVANTAGES OF SSR OVER 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

Aircraft A 80 miles Aircraft C 200 Miles Aircraft B

INTERROGATION SIDE LOBE SUPPRESSION Aircraft A 80 miles Aircraft C 200 Miles Aircraft B P 2 P 1 2 s P 3

Site B PRF 260 Hz Site A PRF 250 Hz unwanted replies rro e Int on i gat F. R. U. I. T.

Correct reply (Frame pulses + 2 information. . ) FRUIT Second PRP First PRP Replies 1 PRF DELAY Coincidence Gate De-fruited video O/P DEFRUITER PRINCIPLE

GARBLE Overlapping replies OVERLAPPING A 4 B 2 D 4 F 2 End of pulse train from aircraft A Beginning of pulse train from aircraft B F 1 C 2 A 2 C 4

TRACK WANDER 1 st sweep 2 nd sweep 3 rd sweep 4 th sweep

TRACK WANDER 1 st sweep 2 nd sweep track

THE MONOPULSE SYSTEM ELIMINATES TRACK WANDER BECAUSE ONLY ONE PULSE FROM A REPLY TRAIN IS NEEDED TO OBTAIN AN ACCURATE BEARING.

BORE SIGHT COMBINED SUM & DIFFERENCE PATTERNS

Mono-pulse Secondary Surveillance Radar MSSR

Cardion Secondary Surveillance Radar Antenna mounted on Tactical Watchman Mounted on T 101 Air Defence Radar

SSR SYSTEM APPLICATIONS MILITARY AIRCRAFT CIVIL AIRCRAFT AIR TRAFFIC CONTROL MARITIME AIRCRAFT MISSILE NAVAL SYSTEMS

MODE S I am able to reply to your “ALL CALL” because I have Mode S Preamble 8. 0 s 0. 5 s This is my discrete address Data block 56 s or 112 s Bit 1 Bit 2 Bit 3 Bit 4 Bit N 1 0 1 0 1 0 0. 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 ?