A method that is disclosed that includes the operations outlined below. Dies are arranged on a test fixture, and each of the dies includes first antennas and at least one via array, wherein the at least one via array is formed between at least two of the first antennas to separate the first antennas. By the first antennas of the dies, test processes are sequentially performed on an under-test device including second antennas that positionally correspond to the first antennas, according to signal transmissions between the first antennas and the second antennas.