A base transceiver station with active antennas in a CDMA mobile communication system, comprising a transceiver installed indoors for up-converting a CDMA-modulated signal to be transmitted to a service subscriber and down-converting a signal received from the subscriber into an intermediate frequency signal, a divider installed indoors for dividing a forward channel signal from the transceiver into a plurality of sector-unit forward channel signals, a coupler for coupling a plurality of sector-unit reverse channel signals and transferring the resultant signal to the transceiver, an antenna interface unit installed indoors for appending a DC voltage to each of the sector-unit forward channel signals from the divider, transferring the resultant sector-unit forward channel signals to a Butler matrix, receiving the sector-unit reverse channel signals from the Butler matrix and transferring them to the coupler, and an active radio frequency module installed outdoors for radiating each beam forming signal from the Butler matrix at a predetermined beam width and predetermined orientation angle over the air, receiving the reverse channel signal from the subscriber, amplifying it and transferring the resultant signal to the Butler matrix.