In air traffic control (ATC) system, a primary radar determines, for example, range and azimuth of an aircraft. The primary radar works in conjunction with a secondary surveillance radar (SSR). The SSR also determines range and azimuth, but additionally altitude and identity. The SSR does this by sending an interrogation message that the aircraft responds to with a message containing identity and altitude information. The aircraft responds to the interrogation message by sending a reply to the SSR using a transponder.
In one aspect, a method includes sending an interrogation request using an omni-directional antenna at a secondary surveillance radar, receiving, from responding aircraft, interrogation responses comprising identity and altitude, determining a distance to each of the responding aircraft based on a time the interrogation request was sent and a time an interrogation response was received, receiving, from a primary radar, positions of tracks, correlating the distances of each responding aircraft with the positions of the tracks to form a set of candidates by position; and sending identity, altitude and position of a track if there is one candidate from the set of candidates.
In another aspect, an apparatus includes circuitry to send an interrogation request using an omni-directional antenna at a secondary surveillance radar, receive, from responding aircraft, interrogation responses comprising identity and altitude, determine a distance to each of the responding aircraft based on a time the interrogation request was sent and a time an interrogation response was received, receive, from a primary radar, positions of tracks, correlate the distances of each responding aircraft with the positions of the tracks to form a set of candidates by position and send identity, altitude and position of a track if there is one candidate from the set of candidates.
In a further aspect, an article includes a non-transitory machine-readable medium that stores executable instructions that cause a machine to send an interrogation request using an omni-directional antenna at a secondary surveillance radar, receive, from responding aircraft, interrogation responses comprising identity and altitude, determine a distance to each of the responding aircraft based on a time the interrogation request was sent and a time an interrogation response was received, receive, from a primary radar, positions of tracks, correlate the distances of each responding aircraft with the positions of the tracks to form a set of candidates by position; and send identity, altitude and position of a track if there is one candidate from the set of candidates.
Described herein are techniques for using a secondary surveillance radar (SSR) that includes an omni-directional antenna rather than a rotating directional antenna. Using an omni-directional antenna provides a low cost solution to air traffic control. In one particular example, the low cost solution includes an SSR working in conjunction with a primary radar that is a phased array radar having a panel architecture.
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Process 100 determines a distance to each responding aircraft based on a time an interrogation request was sent and a time an interrogation response was received (114). In one particular example, process 100 determines the distance to each responding aircraft based on the time the interrogation request was sent, the time the interrogation response was received and a delay. In one example, the delay is a fixed transponder delay. In one example, the fixed transponder delay is based on Radio Technical Commission for Aeronautics (RTCA) DO-181C.
Process 100 receives track data with positions of the tracks from the primary radar 16 (116) and correlates the distances to each responding aircraft to the positions of the tracks from the primary radar (16) (120). A track represents the current estimated position of an object based on multiple radar reports. In one example, a position of a track is designated in azimuth and range. In other examples, the position is designated by latitude and longitude or Cartesian coordinates in the radar plane.
In some instances, there may be more than one distance to a responding aircraft associated with a track. Each distance to a responding aircraft correlated to a track is a designated as a candidate for that position.
Process 100 maintains a set of candidates for each track (126). As data is collected, candidate distances will be eliminated as candidates for the position. If enough data is collected to reduce the set of candidates to a final candidate (132), process 100 sends the identity and altitude of the final candidate with the correlated position of the track (144). In one example, the identity is mode A and the altitude is mode C.
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The processes described herein (e.g., process 100) are not limited to use with the hardware and software of
The processes described herein are not limited to the specific embodiments described herein. For example, the processes are not limited to the specific processing order of the process steps in
Process steps in
While the invention is shown and described in conjunction with a particular embodiment having an illustrative architecture having certain components in a given order, it is understood that other embodiments well within the scope of the invention are contemplated having more and fewer components, having different types of components, and being coupled in various arrangements. Such embodiments will be readily apparent to one of ordinary skill in the art. All documents cited herein are incorporated herein by reference. Other embodiments not specifically described herein are also within the scope of the following claims.