A transmitter, the method of the same, and a communication system using the scheme of space-time block coding employing the multiple beams to mitigate the multipath fading. A transmitter constituted array antennas first performs beams scanning employing beamforming network for estimating the channel space gain pattern, then estimates number of the beams for transmission and the corresponding angles of each beam, performs beam space-time block encoding of input signals then transmitting the encoded signals. The receiver receives the signal and performs linear channel decoding, for example, maximum likelihood decoding.