Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1998-08-21
2001-04-24
Lobo, Ian J. (Department: 3662)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C342S432000, C342S444000
Reexamination Certificate
active
06223123
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in direction finding, especially useful in aircraft collision avoidance systems.
BACKGROUND OF INVENTION
U.S. Pat. No. 5,552,788 describes an antenna arrangement and signal processing which may be incorporated into an aircraft collision avoidance system. Collision avoidance systems are described in U.S. Pat. Nos. 5,077,673, 5,157,615 and 5,388,047, assigned to the assignee of this application. The disclosure of U.S. Pat. Nos. 5,552,788, 5,388,047, 5,157,615 and 5,077,673 are incorporated herein by reference. One of the advantages of the system described in the '788 patent is a simplified arrangement for using multiple direction finding antenna assemblies. In particular, prior to the '788 patent there were systems with multiple directional antenna assemblies for direction finding purposes which used phase encoded directional information. Extraordinary efforts were therefore necessary in those systems to maintain phase balance between the different channels in the equipment. In the absence of such efforts, the directional information could be lost. One of the improvements described in the '788 patent was a modification to the signal processing so that, to a large extent, the direction or bearing information was encoded in amplitude as opposed to phase.
This greatly-simplified the complexity, and as a result limited the cost of the equipment.
As described in the '788 patent, a pair of directional antennas are employed, each pair consisting of a pair of monopole antennas and a hybrid circuit. Preferably, the axes of the pair of directional antennas are orthogonal to each other. One most preferred mounting arrangement is to have one of the directional antennas on an uppermost surface of the aircraft or host, with the other directional antenna mounted on a lowermost surface of the aircraft or host.
Regardless of whether or not the transmitter being located is above or below the host in altitude, one of the pair of directional antennas is in the “shadow” of the body of the host aircraft. If the transmitter being located is above the host aircraft, then the body of the host aircraft will shadow the lowermost directional antenna, and vice versa.
As described in the '788 patent, signals are derived from the pair of directional antennas, the signals are processed and then applied to a table with information allowing the bearing of the transmitter to be located based on the directional antenna signals.
In particular, each directional antenna developed a pair of signals, from the hybrid, whose amplitudes indicated bearing of the transmitter relative to the axis of the directional antenna. A bearing memory stored bearing information as a function of two pairs of inputs. The two pairs of inputs, each pair of inputs from one of the directional antennas, was then applied to the bearing memory so as to develop bearing information.
SUMMARY OF INVENTION
The present invention improves the direction finding method and system described in the '788 patent.
Our studies lead us to believe that because one of the directional antenna's is usually in the shadow of the host, the signals from that antenna are not as reliable for direction finding purposes. In fact, use of both pairs of signals could degrade the direction finding process. Unfortunately it is not possible to limit the system to the use of only one pair of signals since there is an ambiguity in direction finding based only on one pair of the antenna signals. The apparatus of the invention uses only one pair of signals for direction finding but augments that pair by one bit of information from another pair of the antenna signals in order to resolve the directional ambiguity. In addition the apparatus of the invention automatically determines which pair of signals to use for optimum direction finding and therefore derives the additional bit of information for ambiguity resolution from the, otherwise, unused pair of antenna signals.
In particular, of the four signals produced by the two directional antennas, amplitudes of only a pair of the signals are employed in the direction finding process. A comparator or voting logic circuit has, as inputs, both pairs of signals and the voting logic or comparison circuit selects only one of the pair of signals for primary use in direction finding. Both pairs of signals are applied to sign generating circuits. Bearing is determined from the amplitude of the pair of signals selected by the comparison or voting logic circuit taken in conjunction with the output of the sign generating circuit corresponding to the unselected pair of signals.
Since the embodiment of the invention which has been built and tested is digital, use of terms such as “amplitude”, “comparator”, or “circuit” in the preceding description should not be taken as an indication that the implementation is analog; in fact signals taken from the hybrids are digitized so that much of the processing is effected in the digital domain.
REFERENCES:
patent: 3893120 (1975-07-01), Trenam
patent: 3965473 (1976-06-01), Isacson
patent: 4114157 (1978-09-01), Hirata
patent: 4277788 (1981-07-01), Torby
patent: 4724442 (1988-02-01), King
patent: 4780722 (1988-10-01), Cusdin
patent: 5077673 (1991-12-01), Brodegard et al.
patent: 5157615 (1992-10-01), Brodegard et al.
patent: 5388047 (1995-02-01), Ryan et al.
patent: 5463398 (1995-10-01), Young
patent: 5528244 (1996-06-01), Schwab
patent: 5552788 (1996-09-01), Ryan et al.
Ryan Dean E.
Ryan Paul A.
Lobo Ian J.
Morgan & Finnegan , LLP
Ryan International Corporation
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