An antenna modulation method applicable to a transmitter comprising a processing unit which is configured to execute functions including at least but not limited to receiving a symbol represented by a bit stream; converting the bit stream into a coordinate point of a signal constellation comprising a horizontal-axis component and a vertical-axis component; converting, from the horizontal-axis component of the coordinate point, a first vector having at least a first entry and a second entry; converting, from the vertical-axis component of the coordinate point, a second vector having at least a third entry and a fourth entry; generating a third vector having at least a fifth entry and a sixth entry by summing the first vector and the second vector; and activating at least one of the first antenna and the second antennas based on one or more non-zero entries of the third vector.