A smart antenna, a multibeam adaptive antenna beam selection (AABS) planar phased array, has been developed in conjunction with RF technology solutions group, Radio Frequency Systems (RFS). The co-developed Nortel/RFS multibeam antenna produces four precision beams — narrow left, center and right lobes, plus a full-sector beam. The AABS system's advanced array signal processing and adaptive beam algorithm directs and distributes RF energy across three of the four fixed beams, while all four beams are used to receive signals.
The processing back-end also simultaneously suppresses interference signals and takes advantage of the signal path diversity inherent in the multibeam system. As a result, the complete AABS system delivers a more spectrally efficient solution, while allowing more voice and data traffic within existing spectrum.
System trials of the Nortel multibeam technology conducted at a number of Florida PCS CDMA sites over the past three years have demonstrated a two-fold increase in IS-95 voice capacity when compared with conventional single-beam sector antennas. In addition, the AABS demands no change of standards or mobile terminals to achieve these capacity increase benefits. The AABS smart antenna solution conforms to CDMA Development Group (CDG) service operator requirements for smart antenna technology.
The multibeam antenna solution has been precision-developed by RFS to meet Nortel's exacting performance specifications. Along with achieving the required individual beam widths, beam shapes and ‘crossovers,’ electrical downtilts and gains, the antenna has been designed to ensure premium beam-to-beam isolation, return loss and minimal passive intermodulation distortion.
More important, RFS and Nortel have tailored the antenna's performance to ensure minimal interference between the new multibeam antennas and conventional full-sector (single-beam) antennas located elsewhere in the network. To achieve this, great attention has been spent on achieving antenna azimuthal side-lobe levels, elevation beamwidths and electrical downtilts that most accurately match those of conventional sector antennas.