Disclosed is an apparatus for decoupling two antennas in an antenna array, in which the two antennas transmit and receive signals via a first input/output port and a second input/output port of the apparatus. The device may comprise a first adjusting device connected between a first antenna of the two antennas and the first input/output port, a second adjusting device connected between a second antenna of the two antennas and the second input/output port, and one or more decoupling networks connected between the first input/output port and the second input/output port. The first adjusting device and the second adjusting device are configured to have admittance adjustable to compensate an admittance of the decoupling networks such that an isolation coefficient between the two input/output ports approaches zero as well as reflection coefficients of each input/output port are minimized.