Abstract: An apparatus for electronically narrowing the beam width of interrogation transmissions of an interrogator utilizes three beams of the four beam system not used as the main beam for the transmission of suppression pulses. One side of the main beam is suppressed by the first sidelobe suppression pulse of the interrogation pulse sequence and then the other side of the main beam is suppressed by the second sidelobe suppression pulse within the interrogation pulse sequence. In another mode of operation, the interrogation beam width is controlled by transmitting a suppression pulse on a beam positioned 180.degree. from the main beam. This electronic narrowing of the interrogation beam width reduces the number of overlapping replies received by the interrogator and enables the interrogator to properly sort out and not lose or misinterpret replies received by proximity transponder equipped aircraft.

Abstract: A system and method for detecting and removing specular multipath reports from terminal ATCRB systems for aircraft targets having Mode 3/A transponder reporting capabilities. Reports are delayed for a first time, or azimuth, interval to determine whether the report is multipath or to identify future occurrences of multipath reports. After the first azimuth interval, the report is released for display and a fragment of the report is retained for an additional azimuth interval. Of two reports with matching Mode 3/A code, the one with the greater range is considered to be a multipath reply. If the multipath report range falls within a multipath range interval and has not been released for display, it is discarded by the system as an erroneous report.

Abstract: An airborne surveillance method and system allows an observer aircraft to determine the position and change of position of a multiplicity of target aircraft and thus allows analysis of collision threats from these aircraft. The system uses a phase comparison direction finding antenna to determine direction of nearby ground based SSRs and all target aircraft of interest. The system further makes use of all other available data including Mode C transponder generated altitude information of the target aircraft, the altitude of the observer aircraft, the received signal strength of both the SSR beam and the received transponder signal, the time difference of arrival between the SSR interrogation signal and the response from the target aircraft, and a variety of other factors to determine the position of the target aircraft.

Abstract: A virtual secondary surveillance radar (SSR) of the type described in U.S. Pat. No. 4,115,771 can produce inaccurate or indeterminate range information for a transponder positioned near or on a line between the actual SSR and the virtual SSR, owing to unfavorable geometrical relationships. When such condition occurs, the error or ambiquity is resolved by transmitting interrogations from the virtual SSR site toward the actual SSR. The time delay between transmission of an interrogation and reception of a reply to it is a direct measure of the range of the transponder from the virtual SSR.

Abstract: The process for limiting traffic according to the invention comprises an AND input gate receiving the incident pulses representative of the interrogations of the system, its output being connected to an authorization output as well as to a counter which is itself connected to an adder and to a counter, the adder receiving from a memory criteria values, and its output being connected via a reference values memory to the comparator, the output of which is connected via a memory to the said AND gate.

Abstract: A position finding and collision avoidance system derives, at an Own station within the service area of an identified SSr at a known location, differential azimuth (A), differential time of arrival (T), identity and altitude data regarding any transponder-equipped Other station or stations within a predeterminable region surrounding Own station, from standard ATCRBS interrogations and replies. These data are used to compute the positions of Other stations for display at Own station.

Abstract: The invention regards a perfectioning in reply type radar systems, in particular SSR (Secondary Surveillance Radar) or IFF (Identification Friend or Foe). The invention has as its aim that of eliminating or reducing undesired replies due to reflections from fixed obstacles or from structural peculiarities in the main radar system (i.e. radome) and other similar effects. The suppression of undesired replies is attained by varying azimuthally the emission power of the radio-frequency impulses according to a memorized law.