Abstract: The input impedance of antenna array that consists of dual-cylindrical units is investigated. In this paper, the antenna array is separated into two parts: feeding sub-system and radiant sub-system. Simultaneously, the radiant sub-system is equivalent to a N-port network. First, a set of voltage equations is presented according to the transmission line theory, where the voltages, currents, and impedances for each port of network are deduced. Secondly, the relations between total input impedance and that of each port are given. It is indicated that the input impedance of the antenna can be matched by moving the two pistons at the ends. The measured data of the antenna sample verify the results of the calculation.