Abstract:
A transmitter  122  transmits interrogations to aircraft airborne in a coverage, a receiver  123  receives signals transmitted from aircraft airborne in the coverage, reply analyzers  132   b  and  133   b  analyze a reply responding to an interrogation transmitted from the transmitter, as the reply is detected from signals received by the receiver, and a squitter analyzer  132   d  analyzes an extended squitter, as the extended squitter is detected from the signals received by the receiver.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of priority under 35 U.S.C. §119 to Japanese Patent Application No. 2009-118473, filed on May 15, 2009, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Art 
         [0003]    The present invention relates to a secondary surveillance radar (SSR) making use of an extended squitter received from aircraft. 
         [0004]    2. Description of Relevant Art 
         [0005]      FIG. 1  illustrates an SSR  1   a  installed at a ground station. It has a transmitter-receiver  12  adapted for transmission of signals as interrogations to transponders  20  boarded on aircraft  2 , and for reception of signals as replies transmitted from transponders  20  on aircraft  20  in response to interrogations. The transmitter-receiver  12  implements various processes under control of a signal processor  13   a . The SSR  1   a  is adapted for such signal transmission and reception to acquire necessary information for air traffic control. 
         [0006]    There are two types of transponders: an ATCRBS (Air Traffic Control Radar Beacon System) transponder that has been used since ever, and a mode S transponder that has been developed later than the ATCRBS transponder. They employ different signals for transmission and reception. In  FIG. 1 , the SSR  1   a  is an SSR mode S (secondary surveillance radar mode S) system cooperative with both ATCRBS transponder and mode S transponder, so it is adaptive as an SSR for surveillance, even for ATCRBS aircraft (aircraft with an ATCRBS transponder on board), as well as for mode S aircraft (aircraft with a mode S transponder on board). 
         [0007]    As illustrated in  FIG. 2 , the SSR mode S  1   a  has the transmitter-receiver  12  including a transmission-reception selector  121  for selection between signal transmission and reception, a transmitter  122  for transmission of interrogations, and a receiver  123  for reception of replies. Further, the SSR mode S  1   a  has the signal processor  13   a  including a transmission controller  131  for controlling the transmission of interrogations, a mode S reply processor  136  for processing replies received from mode S aircraft, an ATCRBS reply processor  133  for processing replies received from ATCRBS aircraft, a surveillance processor  137  making use of received replies for preparation of target reports to survey flights of aircraft, and a channel controller  134  for controlling transactions in all-call time periods and roll-call time periods. 
         [0008]    More specifically, as illustrated in  FIG. 3 , the receiver  123  includes a Σvideo detector  123   a  for detecting Σvideo from received signals, a digitizer  123   b  for digitizing detected Σ video, a Δvideo detector  123   c  for detecting Δvideo, a digitizer  123   d  for digitizing detected Δvideo, a Ωvideo detector  123   e  for detecting Ωvideo, and a digitizer  123   f  for digitizing detected Ωvideo. 
         [0009]    Further, as illustrated in  FIG. 3 , the mode S reply processor  136  includes a mode S reply detector  136   a  for detecting, from among digitized signals from the digitizers  123   b ,  123   d , and  123   f , mode S replies transmitted from mode S aircraft, and a mode S reply analyzer  136   b  for analyzing detected mode S replies. On the other hand, the ATCRBS reply processor  133  includes an ATCRBS reply detector  133   a  for detecting, from among digitized signals from the digitizers  123   b ,  123   d , and  123   f , ATCRBS replies transmitted from ATCRBS aircraft, and an ATCRBS reply analyzer  133   b  for analyzing detected ATCRBS replies. 
         [0010]    Further, the surveillance processor  137  includes a target report preparer  137   a  adapted to make use of results of analyses by the analyzers  133   b  and  136   b , for preparing target reports. 
         [0011]    The SSR mode S  1   a  is configured, as illustrated in  FIG. 4 , for time division into all-call time periods Ta and roll-call time periods Tr according to, among others, prescribed repetition periods and coverage area, to proceed with processes for acquiring ATCRBS aircraft and mode S aircraft. More specifically, the SSR mode S  1   a  has the transmission controller  131  adapted in all-call time periods Ta for transmission of all-call interrogations to acquire ATCRBS aircraft and mode S aircraft, and in roll-call time periods Tr for transmission of roll-call interrogations to keep acquisition of mode S aircraft having been acquired in all-call time periods Ta, for a processing to enable acquisition of all aircraft within a coverage (refer to Japanese Patent Application Laid-Open Publication No. 2007-248296, and “Secondary Surveillance Radar, Michael C. Stevens, 1998, ISBN 0-89006-292-7”). 
         [0012]    However, the SSR mode S  1   a  may have an increased number of aircraft within the coverage, which might overlap addition of a datalink function, which would constitute a difficulty in acquisition of all aircraft within the coverage, thus shedding light on the importance of efficient use of the periods Ta and Tr. 
         [0013]    In the meanwhile, aircraft is configured to transmit, besides the reply to be transmitted in response to an interrogation transmitted from the SSR mode S  1   a , an extended squitter for use in the ADS-B (automatic dependent surveillance-broadcast). The extended squitter is a signal that is formatted, as illustrated in  FIG. 5A  and  FIG. 5B , with fields of contents including “CA (transponder capability)”, “AA (address announced: transponder mode S address)”, “ME (message extend squitter: aircraft position, velocity, etc)”, and “PI (parity/interrogator identifies)”. The SSR mode S  1   a  may thus receive extended squitters, but is configured to use no extended squitters it has received. 
         [0014]    As having been described, there is a conventional SSR mode S  1   a  that may have an increased number of aircraft within a coverage, which might overlap addition of a datalink function, which would constitute a difficulty to acquire all aircraft within the coverage. On the other hand, there is an extended squitter to be received irrespective of replies, which is not made use of at the SSR mode S  1   a.    
         [0015]    With this point in view, it is an object of the present invention to provide a secondary surveillance radar adapted for utilization of an extended squitter transmitted from mode S aircraft to perform surveillance of aircraft. 
       SUMMARY OF THE INVENTION 
       [0016]    According to an aspect of the present invention, a secondary surveillance radar comprises a transmitter configured to transmit interrogations to aircraft airborne in a coverage, a receiver configured to receive signals transmitted from aircraft airborne in the coverage, a reply analyzer configured to analyze a reply responding to an interrogation transmitted from the transmitter, as the reply is detected from signals received by the receiver, and a squitter analyzer configured to analyze an extended squitter, as the extended squitter is detected from the signals received by the receiver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an illustration of transaction between a typical SSR mode S and a transponder. 
           [0018]      FIG. 2  is a functional block diagram of the SSR mode S of  FIG. 1 . 
           [0019]      FIG. 3  is a functional block diagram of essential portions of the SSR mode S of  FIG. 2 . 
           [0020]      FIG. 4  is a time chart of essential actions of the SSR mode S of  FIG. 2 . 
           [0021]    A and  FIG. 5B  is a set of exemplary formats of extended squitters. 
           [0022]      FIG. 6  is a functional block diagram of an SSR mode S according to an embodiment of the present invention. 
           [0023]      FIG. 7  is a functional block diagram of essential portions of the SSR mode S of  FIG. 6 . 
           [0024]      FIG. 8  is an illustration of lobes of an antenna of the SSR mode S of  FIG. 6 . 
           [0025]      FIG. 9  is a time chart of essential actions of the SSR mode S of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    There will be described the preferred embodiments of the present invention. Like elements to the conventional configuration will be designated by like reference characters.  FIG. 6  illustrates an SSR mode S  1  according to an embodiment of the present invention. Like the SSR mode S  1   a  of  FIG. 1 , the SSR mode S  1  of  FIG. 6  is installed at a ground station, and configured for surveillance of aircraft  2  on bases of transactions with transponders  20  of aircraft  2 . 
         [0027]    As shown in  FIG. 6 , the SSR mode S  1  includes an antenna  11 , a transmitter-receiver  12  configured for signal transmission and reception through the antenna  11 , and a signal processor  13  connected to the transmitter-receiver  12 , and configured to implement transaction control, and prepare target reports to be output in accordance with received replies. 
         [0028]    The transmitter-receiver  12  is provided with a transmission-reception selector  121 , a transmitter  122 , and a receiver  123 , and configured for transmission of interrogations through the antenna  11 , and for handling replies received at the antenna  11  to output to the signal processor  13 . 
         [0029]    The signal processor  13  includes a transmission controller  131  configured to control transmission of interrogations, a mode S reply processor  132  configured to process received mode S replies, an ATCRBS reply processor  133  configured to process received ATCRBS replies, a channel controller  134  configured to schedule transactions in all-call time periods and roll-call time periods, and a surveillance processor  135  configured to make use of replies for preparation of target reports. 
         [0030]    More specifically, as shown in  FIG. 7 , the receiver  123  includes: aΣvideo receiver composed of a Σvideo detector  123   a  for detecting Σvideo from received signals, and a digitizer  123   b  for digitizing detected Σvideo; a Δvideo receiver composed of a Δvideo detector  123   c  for detecting Δvideo from received signals, and a digitizer  123   d  for digitizing detected Δvideo; and a Ωvideo receiver composed of a Ωvideo detector  123   e  for detecting Ωvideo from received signals, and a digitizer  123   f  for digitizing detected Ωvideo. At the receiver  123 , the digitizers  123   b ,  123   d , and  123   f  are each respectively adapted to output digitized video to the mode S reply processor  132  and the ATCRBS reply processor  133 . 
         [0031]    As shown in  FIG. 7 , the mode S reply processor  132  includes: a mode S reply detector  132   a  configured to have digitized Σvideo, Δvideo, and Ωvideo input from the receiver  123 , for detection of mode S replies transmitted from aircraft  2  in response to interrogations the transmitter  122  has transmitted; a mode S reply analyzer  132   b  configured for analyses of mode S replies detected by the mode S reply detector  132   a  to output the results to the surveillance processor  135 ; an extended squitter detector  132   c  configured to have digitized Ωvideo input from the receiver  123 , for detection of extended squitters transmitted from aircraft  2 ; and an extended squitter analyzer  132   d  configured for analyses of extended squitters detected by the extended squitter detector  132   c  to output the results to the surveillance processor  135 . 
         [0032]    As shown in  FIG. 7 , the ATCRBS reply processor  133  includes: an ATCRBS reply detector  133   a  configured to have digitized Σvideo, Δvideo, and Ωvideo input from the receiver  123 , for detection of ATCRBS replies transmitted from aircraft  2  in response to interrogations the transmitter  122  has transmitted; and an ATCRBS reply analyzer  133   b  configured for analyses of ATCRBS replies detected by the ATCRBS reply detector  133   a  to output the results to the surveillance processor  135 . 
         [0033]    As shown in  FIG. 7 , the surveillance processor  135  includes a target report preparer  135   a  configured for use of analysis results of replies and extended squitters to prepare target reports, and a coordinate transformer  135   b  configured to transform coordinates of extended squitters. 
         [0034]    As illustrated in  FIG. 8 , Σvideo is a set of signals received from within a region A of a lobe extending along a center axis of the antenna  11  in a frontward direction f of the antenna  11 . Δvideo is a set of signals received from within regions B of lobes about the frontward direction f of antenna  11 . Ωvideo is a set of signals received from a widespread region C. 
         [0035]    As illustrated in  FIG. 8 , Σvideo and Δvideo appear as directional signals, and can only be used for transactions with aircraft airborne in prescribed (azimuth) ranges with respect to the antenna  11 . On the other hand, Ωvideo appears as a non-directional signal, and can be used for communications with aircraft airborne in a widespread (azimuth) range with respect to the antenna  11 . It is noted that all-call interrogations and replies as well as roll-call interrogations and replies are intended to use simply for targets airborne in the prescribed (azimuth) ranges with respect to the antenna  11 . In use of non-directional Ωvideo, there come replies (fruits, squitters, etc) from any and all transponders as targets. 
         [0036]    More specifically, the extended squitter analyzer  132   d  decodes respective data blocks of extended squitters detected by the extended squitter detector  132   c , and outputs the results to the surveillance processor  135 . Extended squitters are formatted as illustrated in A and  FIG. 5B , including a field of PI (parity/interrogator identifier) to be “0” in value, so the extended squitter analyzer  132   d  outputs a decoded result to the surveillance processor  135 , simply when the PI field has the value “0”, and a field of DF (downlink format) is “10001” in value for DF=17 or “10010” in value for DF=18. 
         [0037]    The coordinate transformer  135   b  transforms positional information contained in extended squitters into positional information compliant with replies. That is, those replies analyzed by the mode S reply analyzer  132   b  or the ATCRBS reply analyzer  133   b  each contain, as positional information of aircraft  2 , such a coordinate (slant range, azimuth) that represents a location of aircraft  2  with respect to the SSR mode S  1 . On the other hand, those extended squitters analyzed by the extended squitter analyzer  132   d  each contain, as positional information of aircraft  2 , such a combination of latitude and longitude that represents a location of aircraft  2 . Therefore, the coordinate transformer  135   b  transforms a combination of latitude and longitude analyzed by the extended squitter analyzer  132   d , into such a coordinate (slant range, azimuth) that defines a location of aircraft  2 . 
         [0038]    The SSR mode S  1  is configured to process also extended squitters received from aircraft  2 , as described. Extended squitters are signals periodically transmitted from aircraft  2 , so the SSR mode S  1  receives such extended squitters at timings independent of all-call time periods Ta and roll-call time periods Tr. Therefore, as shown in  FIG. 9 , the mode S reply processor  132  is adapted to process received extended squitters irrespective of all-call time periods Ta and roll-call time periods Tr. 
         [0039]    More specifically, as shown in  FIG. 9 , the SSR mode S  1  is adapted in each all-call time period Ta to transmit all-call interrogations to mode S aircraft and ATCRBS aircraft, thereby receiving replies, processing (α, β) them, while processing (δ) extended squitters received from mode S aircraft. Further, in each roll-call time period Tr, the SSR mode S  1  is adapted to transmit selective interrogations to mode S aircraft having had replies received by the SSR mode S  1  in past all-call time periods Ta, thereby receiving replies, processing (γ) them, while processing (δ) received extended squitters. In roll-call time period Tr also, the SSR mode S  1  is adapted to process (δ) extended squitters received from mode S aircraft. 
         [0040]    According to the embodiment of the present invention, the SSR mode S  1  makes use not simply of information contained in mode S replies or ATCRBS replies, but also of information contained in extended squitters, for preparation of target reports. Accordingly, the SSR mode S  1  making use of extended squitter is permitted to acquire additional information on aircraft that might not have been caught in any way by conventional transactions only, thus allowing for an enhanced capability in surveillance of aircraft.