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Secondary Radar and Transponder

Secondary Radar and Transponder. Secondary Radar and Transponder. 二次雷达及应答机. Civil Aviation Flight University of China. Secondary Radar and Transponder.

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Secondary Radar and Transponder

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  1. Secondary Radar and Transponder Secondary Radar and Transponder 二次雷达及应答机 Civil Aviation Flight University of China

  2. Secondary Radar and Transponder Air traffic control assumes great importance in civil aviation. Ground controllers need to talk frequency with the pilots flying in the controlled area. They communicate with each other using VHF and HF communication systems. At the same time, the controllers also need to monitor the positions and travellings of airplanes flying within the controlled area. This is realized with the primary surveillance radar (PSR) and the secondary surveillance radar system (SSR). PSR and SSR form the air traffic control radar surveillance system. Civil Aviation Flight University of China

  3. Secondary Radar and Transponder For civilian aircraft, the original secondary radar system derived from the early military IFF(Identification Friend or Foe) is called the Air Traffic Control Radar Beacon System, or ATCRBS. An enhanced secondary radar system that is replacing the ATCRBS system is called mode S air traffic control radar. Civil Aviation Flight University of China

  4. Secondary Radar and Transponder ATCRBS The ATCRBS system is an interrogation-based system that is comprised of a ground-based interrogator and an on-plane transponder. On the ground, an ATCRBS sensor sends out an interrogation signal (using the 1030 MHz frequency band) from a rotating antenna to aircraft flying in its sector. Aircrafts that are equipped with transponders receive these interrogations and send back a reply (using the 1090 MHz band). There are two primary types of interrogations; Mode A and Mode C. Civil Aviation Flight University of China

  5. Transponder Interrogation (1030MHz) Reply (Plane Identification or Altitude,1090MHz) Secondary Surveillance Radar Antenna Side Lobe Primary Suppression Surveillance Antenna Radar Antenna ATC Radar Transmitter Receiver Ground Radar Display Secondary Radar and Transponder Figure 6.1 Civil Aviation Flight University of China

  6. Mode A/C XPDR Radar Antenna Ground Radar Display Transmitter Receiver

  7. Radar Antenna Ground Radar Display Transmitter Receiver

  8. Plane Altitude Interrogation Plane Identification Reply Radar Antenna Ground Radar Display Transmitter Receiver

  9. Secondary Radar and Transponder Interrogations ATCRBS interrogations consist of three pulses. Two of these pulses constitute the interrogation while a third pulse is added to prevent the transponder from replying to the side of the interrogator antenna from one of the side lobes. This pulse is called the side lobe suppression pulse, SLS. Figure 6.2 Civil Aviation Flight University of China

  10. Secondary Radar and Transponder Interrogations The interrogation pulses are P1and P3while the side-lobe suppression pulse is called P2. The time interval between P1and P3determines the type of interrogation, Mode A, Mode B, Mode C, or Mode D. If the P1-P3 timing is 8 microseconds, leading edge to leading edge, a Mode A responses expected, and if 21 microseconds, the request is for Mode C (altitude) data. The SLS pulse, P2always occurs 2μs after P1. Figure 6.3 Civil Aviation Flight University of China

  11. Secondary Radar and Transponder Interrogations If the transponder receives a Mode A interrogation, it transmits the squawk code, as set by the pilot. If it receives a Mode C interrogation, it transmits the altitude code, as supplied by the encoder. It's important to understand that AT NO TIME does the transponder send both. Civil Aviation Flight University of China

  12. Secondary Radar and Transponder Side Lobe Suppression Secondary radar interrogations use a directional antenna that is usually mounted on the primary radar antenna, and thus, is in perfect synchronism with the rotation of the primary antenna. Directional antennas are not perfect in that they will allow some energy to transmit from the side of the antenna. The antenna radiates and receives best in the forward direction. Figure 6.4 Civil Aviation Flight University of China

  13. Side-Lobe Main Lobe

  14. Secondary Radar and Transponder Side Lobe Suppression Replies from the antenna side lobes can be eliminated by transmitting a pulse omni-directionally as a reference level. The radiatedsignal strength of this side-lobe suppression, SLS, pulse is greater than the radiated signal strength from any side lobe. If the interrogation pulses are stronger than the SLS pulse, the interrogation came from the main lobe of the antenna and the transponder replies to the interrogation. If the interrogation pulse is weaker than the SLS pulse, the interrogation was received from a side lobe and thetransponder is suppressed and does not reply. Civil Aviation Flight University of China

  15. Secondary Radar and Transponder Replies Figure 6.4 shows the format of a mode A reply. There is a maximum of 12 data bits, with each data bit having its own time slot. Two non-data bits called framing bits are transmitted to mark the time slots for the data bits. The first framing pulse, called Fl, is the first pulse transmitted, and its leading edge is used for timing. Figure 6.4 Civil Aviation Flight University of China

  16. Secondary Radar and Transponder Replies The first data bit, the C1 bit, is transmitted 1.45μs after the first framing pulse. The second data bit, the Al bit, is transmitted 2.9, is after the first framing bit, and so on, in increments of 1.45μs. Figure 6.4 Civil Aviation Flight University of China

  17. Secondary Radar and Transponder Replies An additional pulse called the special pulse identity, or SPI pulse, is used for an identification function. This bit can be activated by the aircrew by pressing a front-panel switch as directed by the air traffic controller. This pulse causes the display of the aircraft transmitting this pulse to brighten on the radar display as an aid in identifying an aircraft. Figure 6.4 Civil Aviation Flight University of China

  18. Secondary Radar and Transponder The identity code is set into the transponder by the aircrew as instructed by an air traffic controller. When an air traffic controller assigns an identity code, called squawkby pilots and controllers, the pilot is usually asked to identify. “Squawk 1234 and identify” would be a typical instruction from the air traffic controller. At this time, the pilot would set the knobs on the front panel of the transponder to 1234 and press the “IDENT” button. The air traffic controller will see the target on his radar display brighten to verify that the aircraft displayed is the one The SPI pulse is only temporary, and an internal timer removes the pulse 18 sec after pressing the button. Civil Aviation Flight University of China

  19. Secondary Radar and Transponder The Mode C data is pressure altitude, i.e., set to 29.92". The ground equipment automatically adds the necessary barometric correction, according to the local pressure. The controller sees the same reading on his scope that the pilot sees on the altimeter, if both are using the same barometric setting. Civil Aviation Flight University of China

  20. Secondary Radar and Transponder Transponder Control Panel A transponder control panel has four windows which can be set to any number between zero and seven. The reply/monitor light illuminates when you select the test feature to show proper operation. It also flash when the transponder is replying to interrogation signals or transmitting ident pulses. The function selector turns the unit on or off and controls the mode of operation. In the STANDBY position, the transponder is warmed up and ready for operation but does not reply to interrogations. Figure 6.6 Civil Aviation Flight University of China

  21. Secondary Radar and Transponder Transponder Control Panel You usually set your transponder to STANDBY during taxi operations prior to departure. Occasionally, during flight, the controller may direct you to “squawk standby” for operational reasons. The term “squawk” is used by the controller to tell you which transponder function you should select. Figure 6.6 Civil Aviation Flight University of China

  22. Secondary Radar and Transponder Transponder Control Panel As a general rule, you should switch the transponder from STANDBY to ON as late as practical on takeoff. Switch to ALTITUDE if your transponder has Mode C automatic altitude reporting equipment. The ON position selects Mode A and is appropriate when the controller specifies, “stop altitude squawk.” this means you should turn off Mode C altitude reporting but continue to operate your transponder on Mode A. If the controller subsequently needs your Mode C information, the phrase “squawk altitude” will be used. When you land, you should switch your transponder to OFF or STANDBY as soon as practical. Figure 6.6 Civil Aviation Flight University of China

  23. Secondary Radar and Transponder Transponder Control Panel Before using the Mode C information from your transponder for aircraft separation purposes, the controller must make your altitude readout is valid. In case where your altitude readout differs significantly (300feet or more) from your reported altitude, the controller will issue instructions such as, “Stop altitude squawk, altitude differs by 350 feet.” This could mean yourMode C equipment is not calibrated properly or you have an incorrect altimeter setting. The wrong altimeter setting has no direct effect on your Mode C readout, since that equipment is preset to 29.92. However, it would cause your actual altitude to vary from the one assigned by the controller. Be sure to verify that your altimeter setting is correct whenever the controller indicates your Mode C readout is invalid. Civil Aviation Flight University of China

  24. Secondary Radar and Transponder Transponder Control Panel ATC may ask you to “squawk ident”. If so, you should press the IDENT button momentarily and release it. This causes the transponder return to “blossom” on the radar screen for a few seconds. You should be careful to avoid codes 7500, 7600, and 7700 when you are making routine code changes on your transponder. Inadvertent selection of these codes may cause momentary false alarms at radar facilities. Code 7500 alters ATC that an aircraft has been hijacked; Code7600 is used after the failure of two-way radio communications; Code7700 is used foe emergencies. Civil Aviation Flight University of China

  25. Secondary Radar and Transponder Mode S System During the 1990s, a new addressable secondary radar transponder system was installed throughout the world to replace the venerable ATCRBS system. This new system is called mode S —the S means select. The mode S transponder can be made to reply only when that specific transponder is interrogated. This reduces the amount of synchronous garble in the air traffic radar system and allows for more aircraft to be under surveillance. Civil Aviation Flight University of China

  26. Secondary Radar and Transponder Mode S System An important characteristic of the mode S system is that each aircraft has a unique identity. The mode S secondary radar system can have more than 16 million different identities, enough for each airplane in the world to have a unique identity. In addition, there is the ability to transmit data, bi-directionally, between the ground facility and the mode S transponder to aid in air traffic control. Civil Aviation Flight University of China

  27. Secondary Radar and Transponder Mode S System The mode S transponder has some similarities to the ATCRBS transponder. First, the mode S transponder operates on the same frequencies as the older ATCRBS system, that is, the transponder receives interrogations on 1,030 MHz and replies in 1,090 MHz. The transmitter power output is similar to the ATCRBS transponder as is the receiver sensitivity which insures that mode S transponders will have similar service ranges as ATCRBS transmissions. Civil Aviation Flight University of China

  28. There are two categories of mode S interrogations: all-calls and selective. All-call interrogations are just what their name suggests-all transponders of the The all-call interrogations are further subdivided to ATCRBS/mode S all-calls category interrogated reply to the interrogation. and ATCRBS only all-calls. Secondary Radar and Transponder All-Call Interrogations Figure 6.7 Civil Aviation Flight University of China

  29. All-Call Interrogations

  30. Secondary Radar and Transponder All-Call Interrogations An ATCRBS transponder will reply to any of the 4 mode S all-call interrogations. Once an ATCRBS transponder receives P1, P2, and P3, it desensitizes its receiver and initiates a reply. The existence of P4has no effect on the ATCRBS transponder. The mode S transponder, on the other hand, receives P4and determines if a reply is necessary. If the pulse width of P4is 1.6μs, a long pulse, the mode S transponder replies with a mode S reply and not an ATCRBS. If the pulse width of P4is 0.8μs, a short pulse, the mode S transponder recognizes the interrogation as an ATCRBS only and does not reply. Civil Aviation Flight University of China

  31. Aircraft with ATCRBS transponders ignore the last pulse, responding with a normal ATCRBS all-call reply. Mode S transponders see the additional pulse and recognize the signal as a Mode S interrogation, and respond with a Mode S Without this technique, Mode S-equipped aircraft cannot distinguish between an ATCRBS and Mode S interrogation. They will not know which reply to send, and thus cannot interoperate with the different sensors on the ground. reply. Secondary Radar and Transponder All-Call Interrogations Civil Aviation Flight University of China

  32. Secondary Radar and Transponder Mode S Interrogations Selective mode S interrogations consist of two 0.8μs pulses followed by a data block containing either 56 or 112 bits of data. The data block contains the address of the transponder interrogated. Whenever a select type of interrogation is made, the data block is preceded with two pulses of equal amplitude, separated by 2μs. This causes all ATCRBS transponders to suppress, as they would interpret these two pulses as side-lobe suppression. Figure 6.8 Civil Aviation Flight University of China

  33. Mode S Interrogations

  34. Secondary Radar and Transponder Mode S Replies When a Mode S transponder receives either an all-call or normal interrogation, it replies with the same signal (Figure 6.9). This signal has a four pulse preamble and contains a data block with either 56 or 112 bits of information. The four pulse preamble is what identifies this as a Mode S reply. Figure 6.9 Civil Aviation Flight University of China

  35. Mode S Replies

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