The cost-effective Base Station Power Amplifier (BPA) is designed to expand signal coverage through enhancing the downlink transmission power of base station in the area where it is too expensive to build a new base station (BS) or too difficult to choose installation site for a repeater. It is installed close to the BS and amplifies the BS signal via an ultra-linear amplifier unit, then transmits the amplified signal to the Tx antenna input port. A Tower Top Amplifier is usually installed under the Rx antenna as an auxiliary equipment to improve the balance between uplink and downlink.