Abstract: In a method for the detection of the garbling of pulses received by a secondary radar, the secondary radar comprises a monopulse antenna that can be used to obtain a pulse power signal and a pulse difference measurement signal synchronous with the received pulses. The method consists in detecting, at the same time, ripples superimposed on the power signal and ripples superimposed on the difference measurement signal, the presence of at least two garbled pulses being detected by the presence of ripples on at least one of the two signals. Application to the reception circuits of secondary radars.

Abstract: A method of processing a plurality of replies of target aircraft provided in response to interrogation signals from the surveillance aircraft during surveillance periods to determine whether an altitude track may be initialized for use in a traffic alert and collision avoidance system includes the step of selecting three replies, one from each of three consecutive surveillance periods. The replies have binary or coded altitude data of high or low confidence. The binary or coded altitude data of non-adjacent and adjacent replies of the selected replies are compared and an altitude difference value for each of the comparisons is generated. Further efforts to initialize a track are discarded if any of the altitude difference values are greater than first predetermined separated altitudes if and only if such compared non-adjacent and adjacent replies have binary or coded altitude data of high confidence.

Abstract: Disclosed are a method and a device to detect the intermingling, hence the garbling, of pulses received by a secondary radar by phase analysis. The monopulse reception antenna of a secondary radar delivering a sum signal given by its sum channel and a difference signal given by its difference channel, the method according to the invention consists in analyzing the phase difference between the sum signal and the difference signal, the garbling of at least two received pulses being detected by a phase difference with a value that is substantially different from 0.degree. or 180.degree.. Application to the detection of garbled pulses received when the working frequencies of the transponders are very close to one another.

Abstract: In an aircraft which has a tracking system, the aircraft interrogates all target aircraft in the vicinity of the aircraft in order to determine potentially dangerous situations. The interrogation has a predetermined interrogation sequence which includes interrogation pulses and suppression pulses. The target aircraft respond to the interrogation with predetermined parameter information, the target aircraft sometimes responding to the suppression pulses of the interrogation resulting in an indication of false tracks to the monitoring aircraft. A method is implemented which reduces the false tracks resulting from replies to the suppression pulses. The method comprises the steps of forming tracks on responses to the interrogations wherein the responses meet a first set of predetermined criteria. The formed tracks are then identified as suppression pulse tracks or non-suppression pulse tracks in accordance with a second set of predetermined criteria.

Abstract: An SSR reply decoding system for separating pulse codes of a series of closely-spaced or overlapping SSR replies is disclosed. A delay line is connected to receive pulses representing the leading edge of each SSR reply code pulse. The delay line has a length corresponding to at least two bracket lengths of an SSR reply. A bracket decoder is connected to respective taps of the delay line for determining the beginning and end of a first SSR reply. A phantom reply detector is connected to the remaining taps for inhibiting the bracket decoder when two replies are represented by pulses in the delay lines, one of the replies having a pulse space from the pulse of another reply equal to a framing pulse period for an SSR reply. The phantom reply detector therefore inhibits the detection of phantom replies. As a discriminate for determining when pulses having the spacing of a framing period belong to different replies, azimuth data is provided which will permit discrimination of these phantom conditions.

Abstract: A method for inhibiting responses by transponders to interrogation signals originating in the side lobes of an interrogating radar of a secondary radar system. The interrogating radar first transmits a reference signal with the highest power level of the reference signal being directed into a zone of interest to the interrogating radar. The interrogating radar then transmits a control signal having a higher power level than the reference signal in all regions of space except within the zone of interest. The control signal is of substantially longer duration than the reference signal. A transponder receives, detects and measures the peak amplitude of the reference signal and establishes a minimum trigger level (MTL) at a predetermined level below the reference signal peak. The control signal is received, detected and integrated. The peak amplitude of the integrated control signal is compared with the MTL.

Abstract: A system for demodulating and decoding differential phase shift keying (DPSK) transmissions utilizes a bandpass filter, an analog to digital converter and a digital signal processor. Removal of the effects of unknown frequency component is achieved by applying a complex phase correction/rotation factor after DPSK demodulation. The actual phase of the complex signal is never computed directly. All of the processing from Rader decomposition through carrier tracking filter is performed on the complex values and therefore requires only multiplication and addition operations which can be performed at high speed in a microcomputer or in dedicated arithmetic hardware.

Abstract: A defruiter for filtering fruit replies from a reply data signal in a radar system. The defruiter includes a window memory, a main memory, a counter and a main defruiter. Another version of the defruiter includes the items listed above and, additonally, a data memory and a buffer. The window memory stores reply data for a number of range intervals and a number of pulse repetition times. The main memory provides and receives reply data to and from, respectively, the window memory. The counter determines the number of replies occurring in a number of range intervals and a number of pulse repetition times. The main defruiter allows reply data to be provided to a data processor of the radar system when a reply occurs in the center part of the window memory and when the number of replies determined by the counter is greater than or equal to a window parameter. The number of fruit replies occuring within the reply data supplied to the data processor of the radar system is therefore reduced.

Abstract: The present invention is directed to a Mode S uplink or interrogation signal demodulation system which can quickly recognize the Mode S signal and also filter out of noise present in the Mode S uplink or interrogation signal, thereby reducing the bit error rate. To realize this goal the present invention includes a digital differential phase-shift keyed demodulator to demodulate the differential phase-shift keyed data, thereby reducing the time needed to acquire the Mode S uplink or interrogation signal. This digital demodulator also reduces the noise present in the Mode S uplink or interrogation signal and provides an integrated system which is small in structure that can be easily implemented in an aircraft. This Mode S system also includes a preamble and sync phase reversal detection circuit to recognize if the transmitted signal is a Mode S signal. This signal also utilizes Mode A and Mode C detection devices to make the system compatible with present communication systems.

Abstract: A system wherein TCAS transmissions have two jitter components added to the jitter component utilized in the interscan interval to minimize TCAS interference with ground station operation. The jitter components minimize the establishment of false intruder tracks caused by responses to ground station interrogations or interrogations by other TCAS interrogators which are received in synchronism with the TCAS interrogation signals.

Abstract: The device improves the decoding of the replies in S mode deformed by multiple-path phenomena or by imbrication with replies in standard A or C mode. To do this, the device carries out the following in the reception video signal Log .SIGMA. of the secondary radar: determines a pulse level reference value of the data block of the reply by a study of the histogram of the presumed pulse levels of data and compares the level of the reception signal Log .SIGMA. taken at the middle of each time interval that may be occupied by a data pulse with the level reference value, a data pulse being detected or not detected according to the result of the comparison. Should there be a negative result in a baud period, it may recommence similar operations on the angle measurement video signal .SIGMA./.DELTA. if the secondary radar is a monopulse radar.

Abstract: A decoder for separating pulse code modulated messages of the type used in ATCRBS where the messages are identified by two framing pulses separated by 20.3 us. and contain information pulses between the framing pulses separated from the framing pulses and from one another by 1.45 us. The decoder receives an input stream of pulses of uniform width from a Leading Edge Detector which has created the stream from video pulses received from the transmitter of another station. The decoder input pulse stream may contain interleaved pulses from more than one message. The decoder includes an input shift register, an analysis shift register, a plurality of buffer storage devices and additional registers to which selected pulses are fed from the input register for use in determining whether a received message is clear of interfering pulses or whether the message is potentially or actually garbled.

Abstract: An improved Leading Edge Detector/Pulse Quantizer (LED) for use in a pulse code communications system. A prior LED included three shift registers for storing in relative time order, according to the time of reception of video pulse signals by an associated receiver, (a) pulse leading edges, (b) pulse trailing edges and (c) Quantized video (quantized video comprises a pulse having a width equal to the time the received video exceeds a threshold amplitude). The prior LED further included a plurality of logic means for examining the contents of the three registers to determine whether pulse leading or trailing edges of the received video signal were possibly missing because of interference between received video pulses and for inserting extra leading edges in the leading edge register if such extra leading edges could be logically inferred to be present.

Abstract: A method and apparatus for prefiltering received target and fruit replies to filter out more obvious occurrences of fruit replies in an air traffic control system. A detector detects reply signals occurring during sweeps of a radar. After each sweep of the radar, the sweep interval is scanned for the occurrences of reply signals. If a received reply is repeated in any of a predetermined number of successive sweep intervals, then standard sequential observer detection is performed on a larger predetermined number of beam sweeps. If, however, the received reply is not repeated in any of the beam sweeps of the first window, then the signal is considered to be a fruit signal and is discarded.

Abstract: An amplitude detector is disclosed passing only video input signals whose voltage amplitudes are within specified minimum and maximum limits, and is particularly useful in a secondary radar system for filtering out FRUIT, friendly replies to unintentionally interogated targets. A pair of comparators (4 and 31) compare the video input signal (2) against respective first and second threshold voltages (V.sub.th1) and V.sub.th2). The outputs (30 and 33) of the comparators (4 and 31) and AND'ed (34) with each other and with a digitized video signal (32) to actuate a one-shot pulse generator (12) for gating (36) a delayed digital video signal (40) through an output AND gate (22) to yield a video output signal (42).

Abstract: A pulse discriminating system for reply signals and the like in transponders which may independently and correctly discriminate respective pulse trains in the case where a plurality of reply signals are overlapping with respect to time in the transponders. The pulse discriminating system for reply signals and the like in transponders according to the present invention is operated by controlling the gate circuits thereof under a predetermined condition.

Abstract: An improved bracket decoder apparatus including an enhanced bracket decoder ortion and a regenerative bracket decoder portion operates to generate enhanced bracket decode signals and regenerative bracket decode signals. The foregoing combination of decoder portions will allow digital display systems which use IFF information to detect all targets that are replying regardless of the IFF train spacing, even overlapping replies. The enhanced bracket decoder portion of the apparatus can be operated alone to detect all reply conditions except the one of overlapping replies. The apparatus is configured to provide presently used signals also, i.e., the bracket decode, the degarbled bracket decode, and the range and code information for each video reply.