Abstract: A tracking method and system includes receiving a primary radar report after establishment of a real track of the aircraft, determining a false track slant range associated with the aircraft based on an effective altitude of the aircraft above a ground or water surface and an aircraft slant range defined between the radar arranged on the ground surface and the aircraft, determining a capture area based on the false track slant range and an azimuth of the aircraft, and determining whether the primary radar report is a false report by comparing a position of the aircraft determined from the primary radar report to the capture area.

Abstract: A method for detecting conflicts in the II/SI identification code of radars nearby a secondary mode-S radar, includes at least: a first step wherein the radar detects unsolicited unsynchronized replies, i.e. fruits, in a region of extended radar coverage; a second step wherein the radar detects a conflict in II/SI code by analyzing geographic regions of radar coverage common to the radar and to at least one nearby radar, a conflict being detected if the radar: detects, in the region of extended coverage, the presence of fruits that have as source the nearby radar; observes the absence of fruits caused by the nearby radar in that region of radar coverage of the radar which does not overlap with the region of radar coverage of the nearby radar; the region of overlap between the radar coverage of the radar and the radar coverage of the nearby radar forming a region of conflict in II/SI code.

Abstract: A system may include a computing device including a processor. The processor may be configured to: for correlation threads having populated queues, execute at least some of the correlation threads in parallel, wherein execution of each of the at least some of the correlation threads results in at least one of: at least one new radar track or at least one updated existing radar track; and output each new radar track and each updated existing radar track.

Abstract: The present invention provides a low-cost and low-volume mode A/C/S transponder positioning system to detect the position of a target aircraft, or intruder, outside the range of a secondary surveillance radar system. The system uses a signal of the intruder to pinpoint the location of the intruder. The system can be used on both the ground and on an aircraft in a full 360 degree range around the system.

Abstract: A Mode S anti-reflection method for eliminating false tracks due to reflected replies in ground radar systems, wherein the information contribution of the replies (at the level of raw video) is analyzed with the aim of calculating the position of the reflectors. The possible presence of ADS-B reports can be used, otherwise it will be effectuated a geometrical analysis of the distribution of the replies and will be compared with the plot(s) extracted by the radar sensor. The possibility of correlating along time the moving of the plots, their place of origin and average duration of the tracks generated by them will allow to understand whether the plot is relevant to a reflection or not. In the case of “reflection”, a reflectors map is updated automatically in order to avoid the enabling of the initialization of the track in that area.

Abstract: A method for detecting a message provided with a preamble with a number of pulses in a signal sent by an interrogator or a transponder in mode S, said method including a step for decomposition of said signal into an amplitude signal and into a complex phase signal, a step for detection of said preamble by correlating the amplitude signal with a replica signal of the expected pulses, and a phase control step executed by adding together the samples of the phase signal for the duration of the pulses of said preamble and by comparing the sum obtained with a threshold. The method may include a step for time synchronization by correlation of the complex phase signal with a reference sequence formed by one or more known bits before the decoding of the data. The method applies notably to the decoding of interrogation messages borne by low-power signals.

Abstract: Systems and methods for receiving ADS-B messages in environments where multipath propagation corrupts the messages or blocks the reception of the messages. An exemplary system combines RF signal processing and digital signal processing techniques to make it possible to receive ADS-B messages in the presence of multipath reflections from nearby structures and/or farther out structures. The system uses an array of horizontally spaced antennas. The RF signals from the antennas are combined by the receiver so as to form a set of beams with different azimuth antenna patterns to increase the probability that the multipath does not combine destructively with the line-of-sight path in at least one of the beams. This effectively removes multipath reflections where the delay of the multipath relative to the line-of-sight path is less than 100-200 nanoseconds. The system is also configured to remove multipath reflections with greater delays relative to the line-of-sight path.

Abstract: Systems and methods for receiving ADS-B messages in environments where multipath propagation corrupts the messages or blocks the reception of the messages. An exemplary system combines RF signal processing and digital signal processing techniques to make it possible to receive ADS-B messages in the presence of multipath reflections from nearby structures and/or farther out structures. The system uses an array of horizontally spaced antennas. The RF signals from the antennas are combined by the receiver so as to form a set of beams with different azimuth antenna patterns to increase the probability that the multipath does not combine destructively with the line-of-sight path in at least one of the beams. This effectively removes multipath reflections where the delay of the multipath relative to the line-of-sight path is less than 100-200 nanoseconds. The system is also configured to remove multipath reflections with greater delays relative to the line-of-sight path.

Abstract: A method for detecting a message provided with a preamble with a number of pulses in a signal sent by an interrogator or a transponder in mode S, said method including a step for decomposition of said signal into an amplitude signal and into a complex phase signal, a step for detection of said preamble by correlating the amplitude signal with a replica signal of the expected pulses, and a phase control step executed by adding together the samples of the phase signal for the duration of the pulses of said preamble and by comparing the sum obtained with a threshold. The method may include a step for time synchronization by correlation of the complex phase signal with a reference sequence formed by one or more known bits before the decoding of the data. The method applies notably to the decoding of interrogation messages borne by low-power signals.

Abstract: A device for detecting non-phase-modulated pulsed signals includes at least one amplifier receiving a radiofrequency signal, and restoring at least one first signal representative of the envelope of the input signal, and a second normalized signal, characterized in that a module for estimating the stability of the phase includes means for estimating the phase of the radiofrequency signal, and means for evaluating the temporal stability of the phase, the presence of a characteristic pulse being detected if the phase is stable according to determined criteria.

Abstract: The processing method according to the invention is a method of processing replies from targets interrogated by a surveillance radar according to a mode S interrogation of all the targets present in the receiving lobe of the radar, whereby the different targets present in the receiving lobe of the radar are interrogated at least once, the set of the mode S reply signals received for this lobe are collected after each interrogation, a reply detection processing operation is performed for each target and errors are detected and, if necessary, corrected then the corresponding blips are extracted, and this method is characterized in that said signal quality detection and determination processing operation consists in forming a synthetic message with the set of replies to each interrogation for each target, establishing, for each bit of the message, the value and the quality of this bit and performing the error detection and correction using this synthetic message, and the three variables ?, ? and monopulse of all

Abstract: An augmented reality system identifies and controls a vehicle located within an environment. A tracking system obtains viewpoint information corresponding to a real-time view of the environment. A processing system receives information from one or more sensors. Information includes sensor location information and status information about the vehicle. Processing system generates graphics using said sensor location information and said viewpoint information. Graphics include visual representations of said status information and controls. A display displays the generated graphics such that the graphics are superimposed on the real-time view. The graphics appear attached to the vehicle. An interaction device activates a displayed control.

Abstract: Embodiments of the present invention disclose systems and methods for providing an enhanced data link using overlaid modulation. Through embodiments of the present invention, existing ATC (or other) modulated signals using existing standard frequencies may be utilized to transmit (e.g., from an aircraft transponder) additional information in a manner that does not render the transmitted signal unrecognizable by legacy ATC equipment. Legacy equipment will be able to demodulate and decode information that was encoded in the transmitted signal in accordance with preexisting standard modulation formats, and updated equipment can also extract the additional information that was overlaid on transmitted signals.

Abstract: The invention relates to a method for pre-detecting responses in a secondary radar. It applies in particular to the detection of mode S responses. An aim of the invention is to process the signals received before decoding the responses so as to allow the detection of mixed responses, and avoid the detection of ghost responses. For this purpose, the invention has in particular as subject a method for pre-detecting responses in a secondary radar, the responses to be pre-detected comprising a message coded by a modulated signal, characterized in that the presence of a signal exhibiting modulation characteristics in accordance with those of a message of a response to be pre-detected is identified; the duration of the signal identified is measured; this duration is compared with a minimum duration, this minimum duration being determined on the basis of the duration of the messages of the responses to be pre-detected.

Abstract: A secondary surveillance radar system comprising a including a ground system which observes an observation area where an aircraft equipped with a mode S transponder and an aircraft equipped with an ATCRBS transponder possibly coexist, wherein the ground system comprises includes a transmit processor which transmits to the observation area an all-call interrogation signal specific for mode S including an identification code of the ground system, a receive processor which receives a reply signal to the interrogation signal transmitted by the transmit processor, and a recognition processor which recognizes the reply signal as a processing target when identification information included in the reply signal received by the receive processor coincides with the identification code of the ground system, and wherein the recognition processor recognizes the reply signal as the processing target also when the identification information included in the reply signal received by the receive processor coincides with null in

Abstract: The invention applies to secondary radars. It makes it possible to carry out filtering when seeking to detect SSR responses, these SSR responses being overlapped by a mode S response. According to the invention, the pulses of the mode S response are filtered without filtering the pulses of the SSR responses which are of a higher level than the mode S response.

Abstract: Cooperating mobiles (ground vehicles, aircraft) are located and identified by Multilateration and Automatic Dependent Surveillance-Broadcast (ADS-B) techniques using the frequency band and the format of the Secondary Surveillance Radar (SSR) signals in high traffic situations. Standard messages, transmitted by the mobile on the downlink channel, i.e. to a set of fixed receiving stations, and including the identification code, permit the location of the mobile by multiple time measurements (Multilateration) from a subset of the set of fixed receiving stations; when the message contains the position (GPS and, later, Galileo datum) the mobile may be located with the ADS-B when in view even of a few stations or of a single station. In order to overcome the problem that arises with high traffic, i.e. the superimposition of signals, called garbling.

Abstract: The present invention concerns a method and a system for filtering tracks originating from several sources and intended for several clients to which they are supplied. The method comprises at least a phase (8) for establishing a link between tracks resulting from a single aircraft and a phase for selecting one of the linked tracks to represent the aircraft according to a client-dependent criterion, so that a single client may not receive several distinct tracks representing the single aircraft but so that distinct clients may receive distinct tracks representing the single aircraft.

Abstract: The present invention concerns a method and a system for filtering tracks originating from several sources and intended for several clients to which they are supplied. The method comprises at least a phase (8) for establishing a link between tracks resulting from a single aircraft and a phase for selecting one of the linked tracks to represent the aircraft according to a client-dependent criterion, so that a single client may not receive several distinct tracks representing the single aircraft but so that distinct clients may receive distinct tracks representing the single aircraft.

Abstract: A method of classifying radar emitters includes the steps of: (a) receiving pulses from multiple radar emitters; (b) categorizing received pulses based on pulse data descriptors (PDWs); (c) forming clusters of received pulses based on the PDWs; and (d) de-interleaving pulses from the cluster using one of a differential time of arrival (DTOA) histogram technique, a spectrum estimation technique, or a Hough transform technique. Step (a) includes receiving the pulses during a predetermined time interval and storing the received pulses as a snapshot representing the pulses present during the predetermined time interval.

Abstract: Cooperating mobiles (ground vehicles, aircraft) are located and identified by Multilateration and Automatic Dependent Surveillance-Broadcast (ADS-B) techniques using the frequency band and the format of the Secondary Surveillance Radar (SSR) signals in high traffic situations. Standard messages, transmitted by the mobile on the downlink channel, i.e. to a set of fixed receiving stations, and including the identification code, permit the location of the mobile by multiple time measurements (Multilateration) from a subset of the set of fixed receiving stations; when the message contains the position (GPS and, later, Galileo datum) the mobile may be located with the ADS-B when in view even of a few stations or of a single station. In order to overcome the problem that arises with high traffic, i.e. the superimposition of signals, called garbling.

Abstract: A method and system are provided for detecting an edge of a received signal associated with air traffic control communications. The system includes an A/D converter to convert a received signal to a series of digital data samples and an edge detector module to determine a change rate between the data samples. The change rate represents a change in amplitude between the data samples per unit of time. The edge detector module validates an edge of the received signal based on the change rate between the data samples. A decoder module may derive timing information from the leading/trailing edge pulses and associates the reply message with the framing pulse based on the timing information.

Abstract: A method of generating aircraft tactical alerts includes receiving track positions for two aircraft; receiving trajectories and static conformance bounds for the two aircraft; receiving current position for the two aircraft; generating tactical check segments and variable conformance bounds for the two aircraft based on the current position, the static conformance bounds, trajectory, adapted data, and the track positions; and generating a tactical alert if the variable conformance bounds overlap within a specified lookahead time. The variable conformance bounds can be either symmetric or asymmetric about projected tracks. The variable conformance bounds can use step functions, or continuously widening bounds up to the static conformance bounds. The variable conformance bounds can be based on modifying the static conformance bounds in two or three spatial dimensions.

Abstract: A secondary surveillance radar system for use in surveillance of an airspace, which reliably achieves surveillance of the airspace even when an aircraft including a mode S transponder and an aircraft including an ATCRBS transponder are both located in the airspace, wherein both of a time interval between time when transmission of an all-call interrogation signal specific for mode S is completed and time when the transmission of an all-call interrogation signal specific for mode A is started and a time interval between time when transmission of the all-call interrogation signal specific for mode S is completed and time when transmission of an all-call interrogation signal specific for mode C is started is varied in units of one all-call time period.

Abstract: A method of deinterleaving parameter descriptor word (PDW) data includes parallel scoring of pulses in an a posteriori search for associating of pulses based on proximity within a multi-parameter problem space. The a posteriori search includes scoring an oldest pulse against all newer pulses, and then scoring a next oldest pulse against all newer pulses. The associating utilizes at least one of a plurality of parallel computation modes, parallel tasks to operate on separate data fields, and multi-threading or multitasking that can implement one of parallel and configuration-overlaid operation, synchronized by events.

Abstract: Receiving a message including bits corresponding to an identifier, the identifier including a unique address for a aircraft transponder, extracting the unique address from the identifier, comparing the unique address to a set of predetermined addresses, changing selected ones of the identifier bits when the unique address is not one of the set of predetermined addresses, wherein the changing of the identifier bits changes a value of the unique address in the identifier, re-comparing the updated unique address to the set of predetermined addresses and processing the message when the unique address matches one of the set of predetermined addresses.

Abstract: A super resolution processor/receiver to discriminate superimposed secondary surveillance radar (Mode S, Mode A/C) replies and squitter that uses frequency-domain analysis to suppress interference between replies. In particular, the processor/receiver uses a spectral super-resolution method to estimate carriers of reply signals (every reply has a carrier that could be slightly different from the others). These frequency analyses, applied with particular timing referring to the signal that effectively carried the information, allow to estimate the information on SSR Mode S/Mode A/C replies.

Abstract: A super resolution processor/receiver to discriminate superimposed secondary surveillance radar (Mode S, Mode A/C) replies and squitter that uses frequency-domain analysis to suppress interference between replies. In particular, the processor/receiver uses a spectral super-resolution method to estimate carriers of reply signals (every reply has a carrier that could be slightly different from the others). These frequency analyses, applied with particular timing referring to the signal that effectively carried the information, allow to estimate the information on SSR Mode S/Mode A/C replies.

Abstract: Apparatus for processing a signal of a predetermined intermediate frequency (IF) to generate in-phase (I) and quadrature (Q) components thereof comprises: an analog-to digital converter circuit for sampling and digitizing the IF signal to generate digitized data samples thereof at a sampling rate that produces consecutive digitized data samples that are separated in phase by a substantially fixed phase angle 2&pgr;/n, where n is an integer greater than zero; first digital circuitry coupled to the analog-to digital converter circuit for demodulating the digitized data samples by multiplying every n consecutive digitized data samples with n respectively corresponding digital reference samples; and second digital circuitry coupled to the first digital circuitry for combining selected ones of the demodulated samples based on the substantially fixed phase angle to generate digital data samples of the I and Q components of the IF signal.

Abstract: An aircraft system and method for determining when to attempt acquisition of an intruder for active tracking. A link reliability score associated with the intruder is adjusted based upon the signal strength of transmissions, the frequency of the transmissions, and the number of previous attempts to acquire the intruder for active tracking.

Abstract: A method of processing reply signals received in response to an interrogation by a secondary surveillance radar system. The method includes the steps of receiving a reply signal from each of a plurality of targets, and enabling each of a plurality of target mode blocks having a predefined mode to select from the reply signals. The method further includes the step of correlating the selected reply signal to the target mode block that selected same.

Abstract: A target/track assignment method for a combined radar/ADS surveillance environment uses tandem cycles to help the air traffic control system update the order of system tracks, thereby permitting numerous target reports to be processed in real time.

Abstract: The present invention provides a method for efficient use of the transmit power of a Traffic Alert Collision Avoidance System (TCAS) that allows enhanced surveillance range and limits radio frequency (RF) interference in crowded airspace. The method reduces power density in crowded airspace by modifying Mode S, Mode A and Mode C interrogations. During Mode S broadcasts, tracking interrogation power is reduced as a function of range. Further transmit power reduction is achieved by broadcasting a variable power density whisper-shout interrogation technique for Mode A/C aircraft when garbling is detected. If garbling is observed during a medium whisper-shout interrogation sequence, the method of the present invention attempts to clear the garbling by using focused high-density whisper-shout steps but only in the ranges where garbling was detected. Formation members can account for other formation members that are TCAS equipped using a special E-TCAS Broadcast Interrogation.

Abstract: The present invention provides a method for efficient use of the transmit power of a Traffic Alert Collision Avoidance System (TCAS) that allows enhanced surveillance range and limits radio frequency (RF) interference in crowded airspace. The method reduces power density in crowded airspace by modifying Mode S, Mode A and Mode C interrogations. During Mode S broadcasts, tracking interrogation power is reduced as a function of range. Further transmit power reduction is achieved by broadcasting a variable power density whisper-shout interrogation technique for Mode A/C aircraft when garbling is detected. If garbling is observed during a medium whisper-shout interrogation sequence, the method of the present invention attempts to clear the garbling by using focused high-density whisper-shout steps but only in the ranges where garbling was detected. Formation members can account for other formation members that are TCAS equipped using a special E-TCAS Broadcast Interrogation.

Abstract: A transmitter and method for transmitting transponder or TCAS signals uses linear amplification to save on circuit component weight, cost and size while enabling precise amplification and control of the transmitted signal.

Abstract: An SSR reply, which is sent out from an aircraft, is received and separated into one SSR reply to one SSR station and the other SSR reply to the other SSR station, thereby generating aircraft information of the aircraft based on one of the one SSR reply and the other SSR reply.

Abstract: The invention relates to the processing of the multiple paths in an interrogator station which, in response to a salvo of interrogations, receives responses in the form of pulses. The station comprises at least two reception channels. The responses to each interrogation of one and the same salvo are classified by order of appearance. A value of dispersion of the energies is estimated, for each channel and each salvo, on the responses having the same classification. Since the first classified response is, by assumption, considered to have arrived by a direct path, the following responses will be eliminated, on the grounds that they have been received after passing through multiple paths, if their values of dispersion of energy on the two paths are not equivalent to those of the first response.

Abstract: A broadband transmitter element, located at a remote object, transmits a broadband signal at a prescribed transmission time. A broadband receiver element, located at a base platform spaced from the remote object, receives electromagnetic radiation during a reception search window. The broadband receiver element stores information characterizing the broadband signal. A synchronizer synchronizes the broadband transmitter element with the broadband receiver element for timing the transmission and reception. A processing device derives an estimated time of flight for the broadband signal to travel from the remote object to the base platform, and a correlation detector, located at the base platform, identifies the remote object and the arrival time of the broadband signal by correlating the stored information with signals received during the reception search window.

Abstract: A communication system is provided for identifying the position of aircraft in a surveillance area. The communication system includes a dual-frequency interrogator which produces two signals at different frequencies. These signals are transmitted over a narrow beam, scanning antenna, the antenna being located within the surveillance area. A transponder is provided on the aircraft with an auxiliary antenna assembly tuned to a frequency equivalent to the difference between the dual frequencies. The transponder produces a signal containing aircraft identification information. A processing unit is co-located on the aircraft with the transponder to receive the two signals transmitted by the interrogator and produce a signal equivalent to the difference between those signals. The difference signal produced by the processing unit is coupled with the transponder and is used to identify the position of aircraft on the ground.

Abstract: A radar pulse detection and classification system receives times-of-arrival of pulses from simultaneous emitters over a wide range of pulse repetition frequencies (PRF's). The pulses are deinterleaved into bands of pulse repetition intervals (PRI's) so that a fixed number of pulses are required for detection of an emitter regardless of the PRI of the emitter. The pulse periodicities of the pulses in a pulse stream are determined by autocorrelation, and candidate emitter PRI's are selected from the pulse periodicities which were determined by autocorrelation. The pulses of candidate emitters are time-integrated to obtain time-integrated signals, and emitters are detected from peaks in the time-integrated signals. The time-continuity of said pulses are measured to determine emitter existence. The system receives pulses from both jittered and non-jittered emitters.

Abstract: The device comprises an analog-digital converter coupled between a pulse receiver and a device to extract the continuous level of the signal given by the receiver. The continuous level extraction device is coupled to an edge detection device and to a scrambling characterizing device to detect the presence of rising or descending edges and of scramblers in the signal given by the receiver.

Abstract: In a method of communicating data between a transmission/reception center and a target, a transaction is constituted by one or more interrogation pulses sent out by the center followed by one or more associated reception windows designed to receive the response from the target that has been sent the associated interrogation pulse. The length of a transaction is the delay between its interrogation pulse and its reception window, the transactions are classified and positioned according to their distances from the radar in decreasing order. The reception window of each transaction is transmitted immediately before the window of the immediately lower-ranking transaction so long as its associated pulse does not overlap an interrogation pulse of a transaction.

Abstract: Apparatus for associating target reply signals with target signatures, wherein each reply signal is received from a target transponder within a selectable time period, and further wherein each target signature comprises a first set of parameter values that identify a target position and movement relative to an interrogating aircraft, the apparatus including reply processor means for producing a target report for each reply signal, the target report having a second set of parameter values; and report processing means for: 1) comparing each target report with each target signature to identify which report/signature pairs are potential matches, each comparison between a target report and a target signature being based on comparisons of corresponding parameter values to produce a probability of match for each parameter comparison; and 2) identifying which report/signature matches are best based on comparison of each report/signature potential match with each other potential report/signature potential match includ

Abstract: Apparatus for rejecting multipath reply signals received from a target transponder within a selectable time period, comprising: a top antenna and a bottom antenna to detect reply signals; means for determining an altitude code associated with each reply signal detected by the antennas respectively; means for determining a differential time of arrival (DTA) value for each reply signal detected by the antennas respectively; and processing means for: 1) producing, for each top antenna reply signal, a top antenna target report that includes the altitude code and DTA values; 2) producing for each bottom antenna reply signal, a bottom antenna target report that includes the altitude code and DTA data; and 3) comparing each top antenna report data with corresponding data from each bottom antenna report, and marking out each bottom antenna report that is a multipath reply based on such comparison.

Abstract: Disclosed are a device for the detection of S mode responses received by a secondary radar receiver and its use for the filtering of the pulses contained in this response. The device furthermore comprises means to detect a signal S, means for the real-time computation of the mean values of magnitudes characterizing the pulses that belong to the response, and means for the filtration, by comparison, of the values of the magnitudes measured on each pulse detected with the mean value of the corresponding magnitude.

Abstract: A method for the defruiting of the responses from radar transponders received by a secondary radar in response to interrogations sent by the radar recurrently, a recurrence being formed by the interrogation and the responses received during a listening period that follows the interrogation, the defruiting operation consisting in verifying that a response received at an instant T of the recurrence is correlated by the presence of at least r-1 other responses received at the same instant T of their recurrence, these responses forming part of a sequence of at least r recurrences including the current recurrence, the method being one wherein the correlation is achieved over several chosen sequences and wherein the correlation is declared to be positive if it is positive for one of the sequences.

Abstract: Disclosed are a method and device for the real-time processing of the responses constituted by pulse signals emitted by secondary radar transponders. The device has an analyzer of sampled magnitudes characterizing the pulses, said magnitudes being prepared by a device located upline with respect to the disclosed device. This device creates a sample message at the sampling rate. Said sample message characterizes the variations of the different magnitudes from one sample to another. A device for the processing of the pulses receives the sample messages and prepares pulse messages. Finally, a device filters the pulses belonging to a same response from the information elements pertaining to the pulse messages and from response detection signals.

Abstract: A radar processor comprises a multi-port memory device having memory which can be accessed by at least three ports. A first port receives input data from a data providing means. A second port couples a first processor which performs radar processing. A third port couples at least one second processor which assists the first processor by also performing radar processing. The multi-port memory device further includes an arbiter for coordinating and determining when each of the three ports can access the memory of the multi-port memory device. The first and second processors share information with each other via the multi-port memory device.

Abstract: Methods and apparatus for detecting and decoding transponder reply signals of the type having a plurality of associated time discrete pulses including two bracket pulses and a number of related data pulses that may have been transmitted at discrete data time intervals between the bracket pulses such that the signal content detected during the data time intervals corresponds to the reply signal data code, comprising receiver means for receiving the reply signals and producing in-phase (I), quadrature (Q) phase and video (V) signals for each received pulse; means for detecting received pulses and storing the I/Q/V signals in a first memory; means for storing in a second memory pointer values that correspond to the temporal location of pulse I/Q/V signals in the first memory; means for identifying, based on time of arrival (TOA) values, pairs of potential bracket pulses wherein each pair marks the beginning and end of a reply code; and processor means for 1) determining an angle of arrival (AOA) value for each d

Abstract: A method and means for evaluating transponder reply signals in a secondary radar system to differentiate valid replies from false replies. Transponder reply signals received by the interrogating radar are decoded to establish conformity with an established format. All decoded replies to a succession of N interrogation signals are stored in their order of reception in an array of N shift registers. A reply filter is associated with each of the N shift registers. The reply filters operate in parallel to scan the stages of each associated shift register. A unary adder provides the number M of replies detected by the reply filters at each scan step. Reply decision means selects a threshold value that is dependent upon operating conditions of the radar and generates a valid reply signal whenever the value M equals or exceeds the selected threshold value.