Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
1984-04-03
2001-08-14
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S446000
Reexamination Certificate
active
06275189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to passive target location and more specifically to the location of targets by determining the time difference of arrival of electromagnetic emissions between a master station and two stations linearly positioned on either side thereof.
2. Description of the Prior Art
Early in the history of the radar art passive systems, e.g. systems that utilize target generated transmissions as signal sources, were employed to determine the location of radiating sources. Angles to the radiating sources at the two locations, a known distance apart, were determined with receiving antennas having cardioid patterns. The angle to the source being determined when the apex of the cusp of the cardioid was in the direction of the radiating source. The two measured angles and the known distance between the antenna locations were then triangulated to establish the position of the target. Since the angular range of the cardioid pattern cusp were relatively broad, inaccurate angular measurements resulted giving rise to relatively imprecise target location determinations.
Additionally, these systems were operative only in a single source environment. If two or more sources at different locations were emitting signals within the frequency reception band of the system, the system performance was seriously impaired.
Improved accuracy was realized with the advent of monopulse receiving systems. These systems provided significant improvements in the measurement of the angle to the radiated source, thus permitting a more accurate determination of the target location. In a multiple simultaneous signal environment operating within a monopulse beamwidth and within the bandwidth of the system, however, monopulse systems will provide an indication of a single target at a location determined by the angular centroid of the radiating sources. Thus these systems provide useful information of the location of emitters radiating time overlapping signals and operating within the receiver bandwidth only when one emitter is within the monopulse beamwidth. Though monopulse systems may provide target location information when the received signals are time separated, target location ambiguities exist when only two receivers are employed on a baseline.
In addition to the multiple target limitations, prior art systems do not have broadband capabilities and operate only within relatively narrow frequencies band.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention a radiating source location is determined from the reception of emissions from the source at three colinearly positioned receiving stations. The time difference of arrival between the reception of an emission at a centrally positioned receiver, the master station, and two outer receiving locations is determined and utilized with the known receiver separation distances to calculate the angles of arrivals at each of the outer receivers. These angles and the length of the base leg between the two outer receivers determine a triangle that unambiguously positions the target to an accuracy that is primarily a function of the base leg length between stations, improving as this length increases.
Target resolution in a high density target environment may be achieved by restricting the measurement of the time difference of arrival to narrow frequency and space angle bands. This may be achieved with a scannable antenna operable over a multiplicity of selectable radiation bands. Each selected radiation band is further divided into a multiplicity of narrow frequency bands, thus restricting observations to narrow frequency and space angle ranges prior to the determination of time differences of arrival between the master and slave stations. This frequency and angled selection establishes a high probability that the signals processed at the master and slave stations were emitted from a common source.
REFERENCES:
patent: 4393382 (1983-07-01), Jones
patent: 4422076 (1983-12-01), Tricoles et al.
Issing Gregory C.
Levine Seymour
Lockheed Martin Corporation
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