A Low-Profile Dual-Polarized Directional Antenna for Enhancing Channel Capacity in Indoor MIMO Systems

Large channel capacity is achieved by MIMO (Multiple-Input Multiple-Output) technology with multi-antenna at the transmitting and receiving side [1]. Many studies to maximize the MIMO channel capacity have been performed, and measurements show that channel capacity is enhanced by directional antennas [2] and multi-polarization [3] in indoor environment. Various MIMO antennas with pattern and polarization diversity have been proposed, such as combinations of circular patch and monopole [4], and 12 electric dipole antennas at the edges of a cube (MIMO cube) [5]. In MIMO antenna, small and low profile structure are desired for easy installation, and several antennas proposed in [4] and [5] are achieved with compact size. In this paper, we propose uni-directional, dual-polarized MIMO antenna with its thickness of 30 mm. Proposed antenna is designed based on analytical guidelines to achieve large channel capacity shown in [6], and spatially orthogonal beams can be radiated into four directions. This antenna consists of dipole antennas mounted horizontally to the ground plane, and cavity backed slot antennas for vertical polarization. We also propose the application of this antenna to 2  2 MIMO considering antenna spacing at Mobile Station (MS), and show the effect of channel capacity enhancement by MIMO channel measurements in actual environment.