A Blind Adaptive Focused Antenna Array for the Unknown Target in Lossy Medium

This letter presents a novel approach to achieve blind focusing of the electric field radiated by an antenna array on a target that is randomly distributed in lossy medium. The idea is to introduce a test receiving antenna centrally located within the antenna array and to find the excitation distribution of the antenna array by using the sensed scattering parameters between the transmitting array and the test receiving antenna. The excitation distribution of the transmitting array is calculated by using the method of maximum power transmission efficiency. An antenna array consisting of 5 × 5 rectangular microstrip patches loaded with colza oil medium is fabricated to demonstrate the blind focusing scheme with the target being a copper block that is immersed in the oil medium. The results indicate that the transmitting array can adaptively focus the radiated electric field on the copper block once the scattering parameters are sensed, without requiring any a priori knowledge of the geometry and of the electric properties of the target, as well as of its spatial position with respect to the antenna array.