A simple and accurate mathematical model of electronically steerable parasitic array radiator antennas

A new mathematical model of electronically steerable parasitic array radiator (ESPAR) antennas is proposed. The ESPAR antenna is a kind of adaptive array antenna expected to spread as a terminal antenna for home LANs or wireless ad-hoc networks. Parasitic elements loaded with variable-reactance terminations are excited by mutual-coupling, so the current distributions along each wire element are not in the ideal sinusoidal function. To consider the current distributions, an equivalent weight vector (EWV) model is modified by introducing a vector effective length (VEL) for each wire element. The vector effective length of a parasitic dipole can be calculated by the reactance value of the variable reactor loading the dipole. The directivity of ESPAR antennas can be calculated simply and accurately by the EWV-VEL model.