Using a Tunable Transmit-Array Antenna to Improve the Propagation Environment

This letter proposes a method that uses a tunable transmit-array antenna to improve the multiple-input–multiple-output (MIMO) channel capacity in environments that suffer from the keyhole effect. A tunable transmit array of dipole elements is placed at the aperture between two rooms to increase the channel capacity. Varactor diodes are used as load impedances and attached to all dipole elements of the transmit array. This configuration makes the transmit array tunable. The channel capacity can be maximized by individually controlling all elements in the transmit array. The effectiveness of the transmit array in enhancing the channel capacity is confirmed by measurements. The results show that the channel capacity can be improved, and this well supports the effectiveness of the proposed method.