Future communications will provide higher transmission rates and higher operating frequencies. In addition, agile beam tracking will be an inevitable trend in technology development. The terahertz retrodirective antenna array proposed and discussed in this paper can be a better solution for agile beam tracking. The array receives a 40-GHz navigation signal and accurately re-transmits a 120-GHz beam in the direction of the arrival wave. Simulation results indicate that the proposed array with a stacked sandwich structure has realized the tracking of the received wave. The scanning radiation patte shows that the array gain is 23.87 dB at 19.9° when the incident angle is 20° with a relative error of only 0.5%, meaning that there is a lateral error of only 8.7 m at a transmission distance of 5 km.