Soft handoff method and apparatus for mobile vehicles using directional antennas

A method for generating a single beam having at least a pair of lobes for use with an antenna, the method comprising:

• using an antenna to generate a single beam having a pair of independent lobes each forming an independent communications link with a pair of remotely located base stations;
• using a beam former to control an array phase distribution and an array amplitude distribution of signals applied to said antenna that are used to form at least one of the lobes, to thus steer said one lobe in a desired direction independently of the other said lobe;
• the phase distribution of signals for the lobes being accomplished by the beam former determining a plurality of complex voltage distributions required to steer one beam in a corresponding plurality of predetermined directions, and then modifying each of the complex voltage distributions by a blending factor, where the sum of the blending factors used is no greater than 1;
• and
• further controlling said lobes so that a communications handoff is made from a first one of said pair of base stations to a second one of said pair of base stations.

An antenna system for use in communicating with a terrestrial network, where a communications handoff is required to be made by the antenna system from communication with a first base transceiver station (BTS) to communication with a second BTS, the system comprising:

• an antenna controller having information as to the location of the first and second BTSs;
• an antenna component adapted to be carried by a mobile platform;
• a beam forming network responsive to the antenna controller for controlling signals communicated via said antenna component to radiate a single antenna beam having a first lobe having a first gain, and a second lobe having a second gain, with the first and second lobes being independently steerable in desired directions, and with the first and second gains being controllable;
• a phase distribution of signals for the first and second lobes further being accomplished by the beam forming network determining a plurality of complex voltage distributions required to steer one beam in a corresponding plurality of predetermined directions, and modifying each of the complex voltage distributions by a blending factor, where the sum of the blending factors used is no greater than 1;
• and
• the lobes being steerable to enable simultaneously establishing two independent communication links with said BTSs, the BTSs being located at spaced apart locations within two overlapping coverage regions, so that a handoff from the first BTS to the second BTS can be made.

A method for generating at least two independently steerable beam lobes from a single antenna beam of a phased array antenna, comprising:

• using a beam former to:
• determine complex voltage distributions needed to steer a single beam in each one of a plurality of predetermined directions;
• calculate a complex voltage distribution needed to generate the plurality of lobes from the single antenna beam by:
• a) multiplying each said complex voltage distribution by (1−α), where α is a predetermined blending factor having a value between 0 and 1, and such that the sum of the blending factors used is no greater than 1;
• and
• b) adding together the products of a).

A method for generating two independently steerable lobes from a single beam of a phased array antenna, in which the phased array antenna has a plurality of independent antenna elements, comprising:

• using a beam former to:
• a) define a fixed amplitude distribution;
• b) determine a phase distribution needed to steer a single beam in a first direction;
• c) use the amplitude distribution from operation a) and the phase distribution from operation b), to determine a complex voltage distribution needed to steer a single beam in the first direction;
• d) determine a phase distribution needed to steer a single beam in a second direction;
• e) use the amplitude distribution from operation a) and the phase distribution from operation d), to determine a complex voltage distribution needed to steer a single beam in the second direction;
• f) calculate the complex voltage distribution needed to form dual lobes from the single beam by multiplying the complex voltage distribution determined from operation c) by a blending factor (1−α), and adding a quantity:
• (1−α)×(the voltage distribution at operation e);
• and
• g) using the information obtained from operation f), generating an amplitude value and a phase value to be applied to each element of the phased array antenna to generate two lobes aimed in desired directions, from the single beam of the phased array antenna.

A method for generating two independently steerable lobes from a single beam of an antenna, comprising:

• using a beam former to:
• a) calculate a phase distribution needed to steer a single beam from a plurality of elements of said antenna in a first direction;
• b) using a baseline, fixed amplitude distribution for said antenna, together with said calculated phase distribution of operation a), calculate a complex voltage distribution needed to steer a single beam in said first direction;
• c) calculate a phase distribution needed to steer a single beam from said phased array antenna in a second direction different than said first direction;
• d) using the fixed amplitude distribution from operation b), and the phase distribution calculated at operation c), calculate a complex voltage distribution needed to steer the single beam in the second direction;
• e) calculate a complex voltage distribution needed to form a blended dual beam by multiplying the complex voltage distribution obtained from operation b) by a value (1−α), and adding (1−α) times the complex voltage distribution from operation d);
• f) apply the calculation of operation e) to each said element of the antenna;
• g) using the complex blended dual beam distribution from operations e) and f), convert the complex voltage value at each said antenna element to an amplitude value and a phase value;
• h) determine a maximum amplitude value across the elements of the antenna;
• i) subtract the maximum amplitude value obtained at operation h) from the amplitude value at each of the elements of the antenna obtained at operation g) to thus normalize the amplitude distribution across the elements;
• and
• j) apply amplitude values from operation i) and phase values from operation g) to said electronically adjustable attenuators and phase shifters associated with each said element of the antenna to generate the lobes of the single antenna beam.

An aircraft comprising:

• an antenna system for use in communicating with a terrestrial network, where a communications handoff is required to be made by the antenna system from communication with a first base transceiver station (BTS) to communication with a second BTS, the system comprising:
• an antenna controller having information as to the location of the first and second BTSs;
• an antenna component adapted to be carried by said aircraft;
• a beam forming network responsive to the antenna controller for modifying signals applied to said antenna component to cause said antenna component to radiate a single beam having:
• a first lobe,
• selectively a second lobe, with the first and second lobes being independently steerable and controllable to simultaneously establish two communication links with said BTSs, and to effect a handoff of communications with the first BTS to the second BTS;
• and
• a phase distribution of signals for the first and second lobes being accomplished by the beam forming network determining a plurality of complex voltage distributions required to steer one beam in a corresponding plurality of predetermined directions, and modifying each of the complex voltage distributions by a blending factor, where the sum of the blending factors used is no greater than 1.