| Remarkable growth in wireless communications has brought increased demand for transmission capacity, area coverage, and power efficiency. Combined with frequency, code, time, and space division multiplexing techniques, multi-channel antenna arrays are expected to resolve these demands by offering highly efficient and intelligent communication services with beam-steering and beam-forming capabilities.; Planar phased arrays provide delay-and-sum beamforming by controlling the phase of each element, and they increase data capacity by multiplying the diversity gain proportional to the number of elements. However, expensive high-resolution RF phase shifters and complicated control circuits make them impractical for commercial use. Adaptive arrays not only perform main-beam steering for desired signals, but also direct nulls toward interference signals. This optimum pattern control is conferred by advanced adaptive weighting algorithms in the DSP. Their ability to suppress interference substantially improves environmental impairments such as co-channel interference, delay spread, and multipath fading. However, in current digital beamforming architectures, the system throughput is limited by the I/O and signal processing speeds of the digital circuits.; This dissertation presents two types of antenna array systems for cost-effective, high-speed multi-channel wireless communications. First, a frequency-controlled beam-steering array with a mixing frequency compensation scheme is proposed. A very simple phased array structure without RF phase shifters is realized for low-cost base-station antennas. The new feed line structure improves on the bandwidth, beam squint, and RF amplitude imbalance caused by the delay lines in traditional frequency-controlled phased arrays. This array radiates only one beam at a time; however, it enables multi-channel data communication by transmitting multiple RF frequencies in K-band. Two-channel simultaneous RF transmission with a data rate of 50 Mb/s is demonstrated.; Secondly, a high-speed multi-beam adaptive array system is proposed. A new architecture, based on the multi-tone weighting process realized by analog-digital hybrid circuits, enables real-time multi-beam formations and communications with adaptive pattern control. In this architecture, a single beamforming circuit can handle multiple beams, leading to a significant reduction of hardware counts and expenses. The 5.8 GHz eight-element test-bed with two-channel adaptive beamforming capability has been implemented. The measured SDMA performance under simultaneous dual-beam reception is presented. |
