二次雷达（SSR）
电子信息工程学院
16
Pulse pattern
There are five reply modes currently available use as follows: Mode P1 to P3 (us) Purpose Application A 8 ± 0.2 Identity Civil ATC B 17 ± 0.2 Identity Military ATC C 21 ± 0.2 Altitude Civil ATC D 25 ± 0.2 Undefined Unassigned
SSR is a radar system used in ATC/CNS that not only detects and measures the position of aircraft i.e. range and bearing, but also requests additional information from the aircraft itself such as its identity and altitude. Unlike primary radar systems that measure only the range and bearing of targets by detecting reflected radio signals, SSR relies on targets equipped with a radar transponder, that replies to each interrogation signal by transmitting a response containing encoded data. SSR is based on the military identification friend or foe (IFF) technology originally developed during World War II, therefore the two systems are still compatible. Monopulse secondary surveillance radar (MSSR), TCAS and ADS-B are similar modern methods of secondary surveillance.
二次雷达（SSR）
中国民航大学 电子信息工程学院
outline
1. SSR introduction 2. MODE A/C 3. MODE S
二次雷达（SSR）
电子信息工程学院
2
outline
1. SSR introduction 2. MODE A/C 3. MODE S
二次雷达（SSR）
电子信息工程学院
电子信息工程学院
Interrogation Reply
Plane Altitude
Plane Identification
Radar Antenna
Ground Radar Display
二次雷达（SSR）
Transmitter Receiver
电子信息工程学院
SSR：Secondary SurvP3：模式询问脉冲 询问波束（主瓣）辐射 P2： 旁瓣抑制脉冲（控制脉冲） 控制波束辐射
询问 (1030 MHz)
P1 P2 P3
Mode A
8s
Mode C
P1 P2
P3
21s
ICAO规定民用航管二次雷达只采用模式A和模式C交替询问。
二次雷达（SSR） 电子信息工程学院
21
Pulse pattern
P1 and P3 are sent via the directional radar antenna, P2 via an omnidirectional aerial. The spacing between P1 and P2 is constant at 2.0 μ s. Pulse “P2” is used in the electronic side lobe suppression (SLS). The P1 and P3 signals in the main beam are stronger than the omnidirectional P2 pulse, but P2 is stronger than the P1 and P3 pulse received from the side lobes. If the P1 pulse is weaker than the P2 control pulse, then the P1, P3 replies are suppressed.
二次雷达（SSR） 电子信息工程学院
4
Radar Antenna
Ground Radar Display
二次雷达（SSR）
Transmitter Receiver 电子信息工程学院
Mode A/C XPDR
Radar Antenna
Ground Radar Display
二次雷达（SSR）
Transmitter Receiver
3
Limitations of PSR (Why we need SSR?)
Targets that are too small, or are built of a poor radar reflecting material or have a poor aspect may not be detected Targets cannot be identified directly (IFF in the WW2) Radar energy suffers from attenuation (losses) both on the path out to the target and on the return path of the reflections The role of the SSR is to complement the PSR
二次雷达（SSR）
电子信息工程学院
8
PSR vs SSR
二次雷达（SSR）
电子信息工程学院
9
SSR antenna
二次雷达（SSR）
电子信息工程学院
10
SSR characters
SSR is not a true radar system but a two way communications system between an interrogator on the ground and a transponder on the aircraft. However SSR is very similar in operation to conventional radar and suffers from many of the same problems and limitations. Most commercial aircraft are required to be fitted with this equipment for transit through controlled airspace.
二次雷达（SSR）
电子信息工程学院
11
Operation of a Secondary Radar
二次雷达（SSR）
电子信息工程学院
12
SSR workflow
SSR is constituted by one ground-based transmitter and receiver, called interrogator, and one airborne transmitter and receiver, referred to as the ATC transponder, or simply „transponder‟. The interrogator transmits (1030 MHz) pulse pairs, the receiver within the interrogator ‟s beam receives these pulses and decodes them. The transponder then responds by transmitting (1090 MHz) a pulse train (many pulses in a stream) back to the interrogator. The pulse train contains information according to what the interrogator requested.
二次雷达（SSR）
电子信息工程学院
14
outline
1. SSR introduction 2. MODE A/C 3. MODE S
二次雷达（SSR）
电子信息工程学院
15
Pulse pattern
The interrogating transmitter radiates on a frequency of 1030 MHz with a pulse pattern as shown on the right. The radiated pulse pattern includes a control transmission (P2). P2 is arranged to be 9dB lower than P1.The aircraft transponder is designed not to reply unless P1 exceeds P2 by at least 9dB thus suppressing sidelobe returns. The P1 to P2 spacing is fixed(2us). The P1 to P3 spacing is varied according to the type of information required from the aircraft.