Digital beam-forming apparatus and technique for a multi-beam global positioning system (gps) receiver

A global positioning system (GPS) receiver comprising:

• a plurality of antenna elements adapted to receive signals from a plurality of GPS satellites, wherein the plurality of antenna elements is configured as a receiving array that is not contained within a single plane;
• at least one frequency down-converter connected to the plurality of antenna elements and adapted to down-convert the signals from the plurality of antenna elements to at least one of an intermediate frequency and a baseband frequency to form a plurality of down-converted signals;
• a multi-channel receiver comprising a plurality of correlators adapted to correlate the plurality of down-converted signals to create a plurality of correlated signals;
• a GPS-position-processing unit connected to the multi-channel receiver and adapted to extract time and position data from the plurality of correlated signals;
• a memory element adapted to store calibration data comprising beam weighting vectors associated with ones of the plurality of antenna elements;
• and
• a digital beam forming (DBF) processor adapted to:
• apply the beam weighting factors to the plurality of down-converted signals to form a plurality of weighted down-converted signals;
• selectively combine ones of the plurality of weighted down-converted signals;
• and
• create a plurality of coherent beams from combinations of ones of the plurality of weighted down-converted signals;
• and
• an array processor adapted to:
• dynamically select ones of the plurality of antenna elements from which signals are sent to the DBF processor;
• associate ones of the plurality of coherent beams with corresponding ones of the plurality of GPS satellites;
• and
• dynamically alter the beam weighting factors to cause the plurality of coherent beams to track corresponding ones of the plurality of GPS satellites.

In a Global Positioning System (GPS) receiver system comprising a plurality of antenna elements adapted to receive signals from a plurality of GPS satellites within a field of view, a method of determining a direction to a signal source comprises the steps of:

• combining signals from the plurality of antenna elements to form at least a first beam and a second beam, wherein:
• the first beam does not overlap with the second beam;
• and
• the first beam and the second beam taken together substantially cover the field of view;
• independently processing the first beam and the second beam;
• examining the processed data to determine whether the signal source is associated with the first beam or with the second beam;
• reducing the field of view to comprise a region covered by the one of the first beam and the second beam with which the signal source is associated;
• repeating the steps of forming a first beam and a second beam with respect to the reduced field of view, independently processing the first beam and the second beam, examining the processed data, and reducing the field of view, until a direction to the signal source is determined with sufficient precision.

In a Global Positioning System (GPS) receiver system comprising a plurality of antenna elements configured as a receiving array, a GPS position processing unit, a digital beam forming (DBF) processor, an array processor, and a signal-generating unit, a method of calibrating the GPS receiver system comprises the steps of:

• placing the signal-generating unit at a selected calibration location in the far field of the receiving array;
• broadcasting a radio-frequency signal modulated by an acquisition code from the signal-generating unit;
• receiving the signal from the signal generating-unit by the plurality of antenna elements;
• digitizing the signals received by the plurality of antenna elements;
• collecting range data associated with each of the plurality of antenna elements;
• selecting a reference signal from among the signals received by the plurality of antenna elements;
• correlating each one of the signals received by the plurality of antenna elements with the selected reference signal;
• calculating a plurality of beam weighting vectors (BWVs) associated with each of the plurality of antenna elements for the selected calibration location of the signal-generating unit;
• storing the plurality of BWVs in the array processor;
• selecting a new calibration location for the signal generating unit;
• and
• repeating the calibration process for the new selected calibration location.