Repeater consists of antenna, RF duplexer, low noise amplifier, mixer, attenuator, filter, power amplifier and other components or modules, including up and down amplifier links. The basic principle of the system is that the downstream signal of the base station is received by the feedforward antenna (donor antenna) into the repeater, the useful signal is amplified by the low noise amplifier, the noise signal in the signal is suppressed, and the signal-to-noise ratio (S/N) is improved; then the downconverted signal to the intermediate frequency signal is filtered, the intermediate frequency is amplified, and the frequency is shifted up to the radio frequency. It is amplified by a power amplifier and transmitted from a backward antenna (retransmit antenna) to a mobile station. At the same time, the upstream signal of the mobile station is received by a backward antenna and processed by an upstream amplification link along the opposite path: low noise amplifier, down converter, filter, intermediate amplifier, up converter, power amplifier and then transmitted to the base station. So as to achieve two-way communication between the base station and the mobile station. The products used in repeater include dielectric filter, LC filter, LC diplexer, ceramic antenna and so on.