Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2001-05-24
2004-11-09
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
Reexamination Certificate
active
06816117
ABSTRACT:
ORIGIN OF THE INVENTION
The invention described herein was made by employee(s) of the United States government and may be manufactured and used by or for the Government of the United States of America for governmental purpose without payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to distributed antennas and methods and, more specifically, to a distributed antenna with a non-unique phase center that may, in a preferred embodiment, be used for position and attitude determination.
2. Background of the Invention
It is well known that the global positioning system (GPS) may be used for position and attitude determinations whereby the GPS receivers solve the pseudo-range equations. It is also well known that much more accurate position and attitude determinations, within less than one centimeter, can be made utilizing carrier phase measurements in conjunction with the global positioning system (GPS). However, prior art carrier phase location systems may frequently experience problems due to their antenna systems. For instance, especially on moveable items such as vehicles, planes, satellites, thrusters, cell phones, hand-held GPS detectors, and the like, the coverage of the antenna(s) may be limited. Rotation or movement of the item to which the antenna(s) are secured may result in a loss of signal with respect to one or more GPS satellites. While multiple antennas can be utilized to maintain better contact, the need for RF switches, lengthy “times to fix”, and complex switching algorithms, may reduce system reliability and performance while significantly increasing the cost thereof. Moreover, such antenna systems may not be suitably conformable to the surface of the structure upon which they are used so as to be practical, especially for smaller devices such as thrusters, cell phones, satellites, and the like.
While wrap-around antennas, such as spherical and cylindrical antennas, are known to have a wide angle coverage which would theoretically maintain better contact with a plurality of satellites, they also have a non-unique phase center. For instance, if a plurality of satellite signals are received by a wrap-around antenna, there may be a plurality of different phase centers, equal to the number of observed satellites. The position derived using prior art GPS carrier phase techniques requires the position of the antenna phase center. Therefore, the GPS carrier phase solution will be ambiguous when the antenna does not possess a unique phase center. The inventor has determined that it would be desirable to remove the ambiguity resulting from GPS carrier phase measurements obtained with distributed antennas for which the phase center is not unique so as to take advantage of the wide angle of reception afforded by such antennas.
Various inventors have attempted to solve problems as indicated by the following U.S. Patents.
U.S. Pat. No. 5,890,091, issued Mar. 30, 1999, to Talbot et al., discloses a fixed and roving pair of four observable GPS receivers and a communication link between them for double differencing code and carrier measurements. Carrier phase integer ambiguities are resolved efficiently by searching the simultaneous narrow-lane intersections of both the L
1
and L
2
wave fronts propagated by the GPS satellites being tracked. External constraint information, such as elevation, is additionally used to speed up integer ambiguity resolution. Data between the reference station and the rover is communicated in compressed form at a regular interval, e.g., once a second at each epoch, and demi-measurements of carrier phase are obtained more frequently, e.g., ten times a second, and used to propagate solutions between epochs.
U.S. Pat. No. 5,943,008, issued Aug. 24, 1999, to D. L. Van Dusseldorp, discloses a platform attitude determination made with a single receiver in a global positioning system (GPS). The receiver receives at least three sets of GPS signals from three antennas. Two of the GPS signals are delayed so that the receiver receives each GPS signal in separate time domain slots. In this way, the synchronization of separate GPS receivers does not have to be accomplished.
U.S. Pat. No. 5,347,286, issued Sep. 13, 1994, to D. Babitch, discloses a system for automatically pointing a directional antenna. The system comprises two GPS antennas mounted at horizontally opposed extremities of the directional antenna. The placement is such that the GPS antennas lie on a line having a normal vector approximately parallel to a boresight of the directional antenna. The outputs from the GPS antennas are down converted to a measurement frequency and differentially phase compared for each of a plurality of radio visible GPS satellites. A measurement controller receives the phase comparisons. A navigation computer receives measurements from the measurement controller and uses a microprocessor to calculate the GPS latitude and longitude and the attitude angles of the pair of GPS antennas. A servo points the directional antenna at a particular target communications satellite, based on the computed azimuth, elevation, latitude, and longitude, as provided by the navigation computer. One of these servos is used to move the GPS antennas in roughly a circle to average out multipath effects to improve accuracy and reduce integer ambiguities.
U.S. Pat. No. 5,185,610, issued Feb. 9, 1993, to Ward et al., discloses a GPS single-receiver pointing/attitude system which derives pointing/attitude measurements by correlating a selected GPS code (either P or C/A), recovered from GPS navigation signals using a single GPS receiver with multiple GPS antennas (a reference antenna and at least two slave antennas for pointing or three for attitude). For a two antenna pointing application, with a GPS receiver for each receiver channel, the incoming GPS signals are applied to three code correlators assigned to the reference antenna, and three code correlators assigned to the slave antenna, which provide corresponding reference and slave I and Q correlation outputs. The single-receiver pointing technique involves: (a) using the reference I and Q correlation outputs to establish a conventional reference antenna tracking loop; and (b) processing the reference and slave I and Q correlation outputs (using differential carrier doppler phase or code phase measurements) to determine phase differences from which pointing can be computed.
U.S. Pat. No. 5,477,458, issued Dec. 19, 1995, to P. V. W. Loomis, discloses method and apparatus for providing GPS pseudo range correction information over a selected geographic region S with a diameter of up to 3000 km with an associated inaccuracy no greater than 5 cm. N spaced apart GPS fiducial stations, whose location coordinates are fixed and known with high accuracy, are provided within or adjacent to the region R. Each fiducial station receives GPS signals from at least four common-view GPS satellites, compares these coordinates with its known location coordinates, determines the pseudo range corrections for its GPS-determined location, and transmits these correction signals to a central station located within or adjacent to the region S. The central station retransmits the pseudo range correction signals throughout the region S. A mobile GPS station within or adjacent to the region S has stored within it coordinates of the GPS determined last location of that mobile station and the spatial coordinates of GPS fiducial stations within S that are closest to the last determined location of that mobile station. The mobile station then computes the differential GPS corrections for the GPS-determined present location of that mobile station. Alternatively, the fiducial stations can transmit to the central station unprocessed GPS signals for determination of the pseudo range correction signals at the central station. This approach can be modified if the region S is two-dimensional, where only one coordinate is needed.
U.S. Pat. No. 5,587,904, issued Dec. 24, 1996, to Ben-Yair et al., dis
Dobbins Justin A.
Fink Patrick W.
Cate James M.
Issing Gregory C.
The United States of America as represented by the United States
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