Takafumi Ohishi

A method to improve the correlation coefficient and the mutual coupling for diversity antenna

Wireless LAN systems employ diversity antennas to reduce the effects of multipath fading. When several antennas are provided in close proximity, the radiation patterns becomes similar to one another and the diversity gain decreases. Moreover, the radiation efficiency decreases due to mutual coupling between antennas. In order to increase the diversity gain, a method to improve the correlation coefficient among the antenna elements by mutual coupling between antenna elements has been reported (Sawaya, K. et al., 1982). However, this leaves the problem of a decrease in the radiation efficiency caused by mutual coupling. The paper proposes a new method to improve the correlation and the mutual coupling between antennas simultaneously. A slit is provided on a finite ground plane with antennas. The slit changes the current distribution on the ground plane. This change of current distribution causes differences between antennas in the radiation pattern and a pattern diversity effect is achieved. This diversity effect improves the correlation coefficient without applying mutual coupling. Additionally, by changing the current distribution, the mutual coupling is improved and the radiation efficiency increases under low correlation conditions.