Method and apparatus for miniaturization of MIMO systems via tightly coupled antenna array

An apparatus comprising:

• processing circuitry configured to generate Multiple Input Multiple Output (MIMO) signals in a wireless propagation channel using antenna array port orthogonal modes:
• an antenna array comprising at least two tightly coupled antennas at a first frequency, a memory configured to store a plurality of instructions, wherein the plurality of instructions are configured to cause the processing circuitry to:
• acquire an antenna array port scattering matrix S at a first frequency;
• calculate a set of antenna array port orthogonal modes, wherein the set of antenna array port orthogonal modes include antenna array port characteristics modes, array port Inagaki modes, array port scattering matrix modes, based on antenna array port scattering matrix S at a first frequency;
• order the antenna array port orthogonal modes at a first frequency based on a system performance criteria, the system performance criteria comprising one or more of:
• a maximum modal significance parameter a, a maximum radiation efficiency, a maximum SINR at the user, a minimum interference at the user, and a maximum capacity;
• derive antenna array excitation coefficients at a first frequency from the antenna array port orthogonal modes at a first frequency;
• and
• apply the antenna array excitation coefficients as antenna array port excitation weights.