A communications apparatus, comprising an antenna apparatus, the antenna apparatus comprising: N antenna ports and M directional polarization antennas, wherein M is K times 4, N is an integer multiple of 4, N and M are integers greater than 0, and K is an even number greater than 0; and the M directional polarization antennas are evenly distributed on four surfaces of a cube, each surface comprises K directional polarization antennas, a polarization direction of K/2 directional polarization antennas on each surface is a first polarization direction, and a polarization direction of other K/2 directional polarization antennas on each surface is a second polarization direction; on two neighboring surfaces or two opposing surfaces of the four surfaces, K directional polarization antennas in a same polarization direction are combined into one channel, and are connected to one of the N antenna ports, and each of the N antenna ports is connected to the K directional polarization antennas, wherein the communications apparatus further comprises a processor, characterized in that the processor is configured to obtain, for each of the M directional polarization antennas, P signal measurement values that are separately obtained through measurement of the each of the M directional polarization antennas within a preset time period, wherein P is an integer greater than 0; and when an average value of the P signal measurement values corresponding to one directional polarization antenna in X directional polarization antennas is greater than a sum of an average value of P signal measurement values corresponding to one directional polarization antenna in a transmit antenna currently used by the communications apparatus and a first preset threshold, Y directional polarization antennas with a maximum average value of the P signal measurement values in the M directional polarization antennas are used as a transmit antenna, wherein Y is less than or equal to M, and Y is greater than or equal to 1; the X directional polarization antennas are directional polarization antennas that are in the M directional polarization antennas and that are other than the transmit antenna currently used by the communications apparatus; and X is an integer greater than 0. N antenna ports and M directional polarization antennas, wherein M is K times 4, N is an integer multiple of 4, N and M are integers greater than 0, and K is an even number greater than 0; and the M directional polarization antennas are evenly distributed on four surfaces of a cube, each surface comprises K directional polarization antennas, a polarization direction of K/2 directional polarization antennas on each surface is a first polarization direction, and a polarization direction of other K/2 directional polarization antennas on each surface is a second polarization direction; on two neighboring surfaces or two opposing surfaces of the four surfaces, K directional polarization antennas in a same polarization direction are combined into one channel, and are connected to one of the N antenna ports, and each of the N antenna ports is connected to the K directional polarization antennas, wherein the communications apparatus further comprises a processor, characterized in that the processor is configured to obtain, for each of the M directional polarization antennas, P signal measurement values that are separately obtained through measurement of the each of the M directional polarization antennas within a preset time period, wherein P is an integer greater than 0; and when an average value of the P signal measurement values corresponding to one directional polarization antenna in X directional polarization antennas is greater than a sum of an average value of P signal measurement values corresponding to one directional polarization antenna in a transmit antenna currently used by the communications apparatus and a first preset threshold, Y directional polarization antennas with a maximum average value of the P signal measurement values in the M directional polarization antennas are used as a transmit antenna, wherein Y is less than or equal to M, and Y is greater than or equal to 1; the X directional polarization antennas are directional polarization antennas that are in the M directional polarization antennas and that are other than the transmit antenna currently used by the communications apparatus; and X is an integer greater than 0.