Development of Adaptive Array Antenna for Mobile Handsets

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With the recent development of high-speed communications network, high-speed wireless communication system is also desired. However, it is difficult to obtain high-speed wireless system because of the limitation of frequency resources. In order to overcome this difficulty, application of adaptive array antenna system to mobile handsets is required. In the present research, mutual coupling among antennas mounted on a mobile handset has been analyzed and compensation technique of the mutual coupling has been developed. Limitation of the suppression of interference signal in the case of adaptive array antenna for mobile handsets has been also investigated.1. Compensation of mutual coupling among antennas mounted on mobile handset For the compensation of mutual coupling, a method, in which the data of mutual coupling are calculated and stored to obtain the array element pattern, has been developed. Numerical simulation of DOA (direction of arrival) estimation using array antennas composed of a monopole antenna and an inverted planar F-shaped antenna and experiments are performed confirming the validity of the proposed method.2. Investigation of limitation of interference suppression performance Performance of interference suppression is evaluated by using a W-CDMA receiver for 4 element adaptive array antenna at 2.45 GHz, which was developed by the present investigators. Experiment using 4 element monopole array antenna for line-of-sight and non-line-of-site propagation paths shows that a quarter wavelength array spacing is enough to suppress the interference for the case of line-of-sight. On the other hand, the array spacing should be longer than a half wavelength when the propagation path is non-line-of-site. Experimental investigation of the performance of interference suppression for a receiver having frequency domain equalizer for 2 element array antenna has been also performed.