With the high-speed development of mobile communication and the increasingly complex communication environment, multibeam antennas are widely required in the application fields of multi-target radar, satellite communication, multi-point wireless communication, etc. Orbital angular momentum is one of the fundamental properties of electromagnetic waves. It has a spiral wavefront and is independent of basic properties such as amplitude, phase, and polarization. It can provide a new multiplexing dimension for electromagnetic waves. Based on the excellent electromagnetic control capability of the sub-wavelength metal waveguide array, we designed a multibeam rotatable terahertz (THz) array antenna. By adjusting the phase distribution of two orthogonal polarization components of the incident wave, they can be transformed into two vortex beams with the same intensity distributions and opposite orders. The interferometric patterns in the 45° polarization direction can be rotated by changing the phase difference between the two components. Moreover, the array antenna also shows the performance of high gain (31 dBi) and wide bandwidth (up to 61 GHz). This work can provide a new way for azimuth measurement based on multibeam array antennas and is of great significance to enrich the design of array antennas in the THz band.