Adaptive control algorithm of ESPAR antenna based on stochastic approximation theory

The electronically steerable passive array radiator (ESPAR) antenna is one kind of the parasitic elements based single-port output antennas with several variable reactances. It performs analog aerial beamforming and none of the signals on its passive elements can be observed. This fact and one that is more important-the nonlinear dependence of the output of the antenna from adjustable reactances-makes the problem substantially new and not resolvable by means of conventional adaptive array beamforming techniques. A novel approach based oil stochastic approximation theory is proposed for the adaptive beamforming of the ESPAR antenna as a nonlinear spatial filter by variable parameters. thus forming both beam and nulls. Two learning rate schedule were examined about output SENR. stability, convergence, misadjustment, noise effect, bias term, etc.. and the optimal one was proposed. Further development was traced. Our theoretic, study, simulation results and performance analysis show that the ESPAR antenna can he controlled effectively. has strong potential for use in mobile terminals and seems to be very perspectives.