Optimization of MIMO-beamforming and null-steering on small, wireless terminals

In this paper a new approach has been presented to improve the beamforming and null-steering capabilities of small, wireless terminal antennas. Due to the reduced number of antennas and the crucial environmental influences (antenna separation, battery, small groundplane), the beamforming performance is limited. Especially in the case of null-steering the achivable attenuation of the nulls is very low. It has been shown, that using parasitic coupled elements, loaded with appropriate impedances, improve the beamforming capabilities. A simplified model of a realistic terminal with two antennas and a single parasitic element has been presented. Using four switchable load impedances at the parasitic element, the null-steering level can be improved in the complete azimuthal range. Improvements of about 14 dB can be achieved.