An adaptive array for a frequency division duplex (FDD) system requires calibration among the antennas, the cables, and the transmitters and receivers to form the desired transmission directivity. In this paper, we propose the Automatic Calibration method of adaptive array using Transmitting signals for FDD systems with Linear array (ACT-FL) by using the signal circulation among the antennas and not using any additional elements or external information for calibrating the antennas and cables. By studying the calibration accuracy of the ACT-FL through analysis and tests including the mutual coupling of the antennas, we explain the applicable element spacing and the beam width in ACT-FL. We also evaluate the signal-to-interference power ratio (SIR) at the interference arrival time from radiation pattern measurements by using a testbed implementing ACT-FL and demonstrate the effectiveness of ACT-FL. (C) 2004 Wiley Periodicals, Inc.