A method to generate multiple input multiple output, MIMO, signals in a wireless propagation channel using antenna array port orthogonal modes, the method performed by an apparatus comprising: measuring, by processing circuitry (2225, 2215) of the apparatus, an antenna array port scattering matrix at a first frequency from an antenna array of the apparatus comprising tightly coupled antenna array elements; determining, by the processing circuitry (2225, 2215), a set of antenna array port orthogonal modes, wherein the set of antenna array port orthogonal modes include antenna array port characteristic modes based on the antenna array port scattering matrix at the first frequency; determining, by the processing circuitry (2225, 2215), an ordering of the antenna array port characteristic modes at the first frequency based on a system performance criteria, the system performance criteria comprising one or more of: a maximum modal significance parameter, a maximum radiation efficiency, a maximum signal to interference noise ratio, SINR, at a user terminal, a minimum interference at the user terminal, and a maximum capacity of a system in which the apparatus is configured; determining, by the processing circuitry (2225, 2215), antenna array excitation coefficients at the first frequency based on the ordering of the antenna array port characteristic modes at the first frequency; and applying, by the processing circuitry (2225, 2215), the antenna array excitation coefficients as antenna array port excitation weights, wherein the maximum modal significance parameter is determined based on a magnitude of a modal eigenvalue for each of the antenna array port characteristic modes, wherein the maximum modal significance parameter, α, is in a range of [0, 1], and wherein the maximum modal significance parameter is given as: α = 1 1 + λ, wherein λ is an eigenvalue for each mode. measuring, by processing circuitry (2225, 2215) of the apparatus, an antenna array port scattering matrix at a first frequency from an antenna array of the apparatus comprising tightly coupled antenna array elements; determining, by the processing circuitry (2225, 2215), a set of antenna array port orthogonal modes, wherein the set of antenna array port orthogonal modes include antenna array port characteristic modes based on the antenna array port scattering matrix at the first frequency; determining, by the processing circuitry (2225, 2215), an ordering of the antenna array port characteristic modes at the first frequency based on a system performance criteria, the system performance criteria comprising one or more of: a maximum modal significance parameter, a maximum radiation efficiency, a maximum signal to interference noise ratio, SINR, at a user terminal, a minimum interference at the user terminal, and a maximum capacity of a system in which the apparatus is configured; determining, by the processing circuitry (2225, 2215), antenna array excitation coefficients at the first frequency based on the ordering of the antenna array port characteristic modes at the first frequency; and applying, by the processing circuitry (2225, 2215), the antenna array excitation coefficients as antenna array port excitation weights, wherein the maximum modal significance parameter is determined based on a magnitude of a modal eigenvalue for each of the antenna array port characteristic modes, wherein the maximum modal significance parameter, α, is in a range of [0, 1], and wherein the maximum modal significance parameter is given as: α = 1 1 + λ, wherein λ is an eigenvalue for each mode.