1. A method for estimating an admittance matrix of an antenna with a plurality of sub-wavelength antenna elements for radiation patterning, comprising: generating a sequence of port impedance vectors, {z (m) , m=1,. .. , N m }, wherein each port impedance vector, z (m) , of the sequence has a length, N, and corresponds to a set of impedance values for a plurality of tunable impedance elements in communication with a plurality of sub-wavelength antenna elements, and where a number, N m , of port impedance vectors of the sequence is at least as large as a number of unknown admittance parameters, N u , of an unknown admittance matrix; obtaining S-parameters, S (m) , of a scattering matrix, (S-Matrix), for each port impedance vector, z (m) , of the sequence by: applying the set of impedance values for the plurality of tunable impedance elements to the plurality of sub-wavelength antenna elements, and measuring at least one S-parameter for the applied set of impedance values for the plurality of tunable impedance elements; generating a simulated S-Matrix by associating each of the port impedance vectors, z (m) , with the unknown admittance matrix; determining a plurality of optimization variables by comparing each of the S-parameters, S (m) , to the simulated S-Matrix for each port impedance vector, z (m) ; and generating an estimated admittance matrix by associating each of the optimization variables with the unknown admittance parameters.