Optimal design of antenna arrays for microwave power transmission with multiple receiving targets in the radiative near-field

This study proposes a method for maximizing the beam collection efficiency (BCE) for a microwave power transmission system with multiple receiving targets in the radiative near-field region. The electric and magnetic fields of the transmitting array are calculated via the superposition principle. Through theoretical derivation, the BCE maximization problem is simplified into finding the maximum ratio of two real quadratic forms. Based on the theory of matrices, the optimal BCE and its corresponding excitations of the transmitting array can be determined by finding the largest characteristic value and its associated characteristic vector. In practice, the required power for multiple receiving targets may be different. To meet this requirement, a BCE optimization model is established, considering the constraints of the problem of allocable power for each receiving target. A hybrid grey wolf optimizer and Nelder–Mead simplex method is adopted to address the optimization problem. To verify the effectiveness of the proposed method, numerical experiments on focusing the power radiated on two parallel receiving targets are conducted first. Then, two rotating receiving targets are employed to show its universality. Finally, three and four receiving targets are adopted to further evaluate the validity of the proposed method.