摘要 : An expression of an ESPAR antennas's radiation pattern as an expansion with the coefficient of port currents or port voltages is proposed. The expansion function of a port current is a radiation pattern when each port is excited b... 展开 An expression of an ESPAR antennas's radiation pattern as an expansion with the coefficient of port currents or port voltages is proposed. The expansion function of a port current is a radiation pattern when each port is excited by a unit port current and the other ports are opened. That of a port voltage is a radiation pattern when each port is excited by a unit port voltage and the other ports are shorted. The expansion coefficients, port currents or port voltages, can be calculated from the control parameter, reactance values, by means of admittances between the ports. The influence of a grand plan is considered in the admittances, so it affects to the expansion coefficients. The influence of grand plane is also considered in the expansion function, together with the interaction of elements and the current distributions along the wire elements. The expansion function expresses the antenna structure including the grand plane. And the expansion function can be expressed by a function of a normal steering vector, when the ESPAR antenna has no grand plane. So we call the vector composed with the expanssion functions as an equivalent steering vector. As the admittances and the equivalent steering vector are uniquely determined depending on the antenna structure, the variable directivity can be easily calculated by finding the parameter only once and memorizing them. 收起