Steered beams are essentially the combination of two technologies: Beam-forming and beam steering.
Beam-forming is achieved by using phased array antennas to create a narrow beam directed at each mobile in the downlink. The antenna elements form a phased array antenna that have very small spacing (usually half a wavelength). By virtue of the small spacing, transmitted signals from the array antennas are added constructively in one particular direction and are added destructively (or nullified) in all other directions. The net effect is a narrow pencil-shaped beam. In contrast, transmit diversity antennas have to be spaced at multiple wavelengths to reduce the correlation between the propagation paths and produce a diversity gain.
Beam steering is achieved by altering the signal phases that feed each of the antenna array elements. This alters the direction in which the signals are added constructively. Feedback information from the mobile terminal is required to continuously alter the phases in such a way that makes the beam follow the mobile as it is moving.
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