Sky-Net Project surveys a concept to establish a mobile communication from airborne. A base station transceiver (BTS) is carried on an aerial vehicle to relay mobile users to ground base station. The Sky-Net System is designed for a temporary communication environment for emergency and disaster rescue in remote areas. An eCell BTS is selected for microwave downlink which requires high precision line-of-sight (LOS) antenna alignment. Two directional antennas for horizontal and vertical polarization are installed on airborne to track the ground receiver. To overcome the dynamic flight characteristics, a real time servo control system is developed on a microcontroller-based on GPS and AHRS feedbacks to accomplish high accuracy requirement for 5.8GHz microwave system. The UAV and ground station are exchanging their 10Hz GPS data and linking via 900MHz and 5.8GHz wireless modules for higher reliability. By reading the difference of attitude and position data, the ground antenna is tracking the UAV through the servo control system. The airborne unit reads AHRS and ground GPS data to control the tracking servo mechanism to align the airborne antenna onto ground antenna. The Euler's angles GPS and flight data are read to determine an appropriate angle for antenna alignment to ground antenna. The antenna tracking system is completed as the preliminary technology for further Sky-Net Project in real flight verifications with very stable antenna alignment for LOS microwave transmission.