Optimization of antenna directivities for multiple antenna systems by using spherical mode expansion

MIMO antenna design is one of biggest issues in the LTE deployment. The multiple antennas should be designed compactly without sacrificing radiation efficiency and spatial correlation. Such multiple antennas can be achieved with polarization antennas or decoupling elements. Conventionally, these antenna parameters are designed empirically. In this paper, a method to optimize multiple antenna directivities is developed by using spherical mode expansion. The optimal antenna directivities can be obtained as spherical mode coefficients that maximize average channel capacity of such multiple antenna systems.