Antenna system having an antenna array with multiple sub-arrays, each having one or more antenna elements, is calibrated using a distributed calibration antenna element, such as a leaky coaxial cable, that spans across at least two and possibly all of the sub-arrays. To calibrate the transmit (TX) paths of the sub-arrays, TX calibration test signals are transmitted by the sub-arrays, captured by the distributed calibration element, and processed by a corresponding calibration radio. To calibrate the receive (RX) paths of the sub-arrays, an RX calibration test signal is generated by the calibration radio, transmitted by the distributed calibration element, captured by the sub-arrays, and processed by their corresponding radios. Cross-correlation between the calibration and captured signals is performed to derive the complex gain of each sub-array transmitter and receiver, which provides information for aligning the gain, phase, and delay of the different TX and RX paths of the antenna array.