The difference between duplexers and circulators

　　Duplex is a three port passive RF device, which is an extremely common RF component used in transmitter circuits, receiver circuits, and transceiver circuits for communication, radar, and other sensing purposes.

　　Duplex allows two different devices to share a common communication channel. It consists of two filters of different frequencies (low-pass, high pass, or band-pass) connected to an antenna. By utilizing the frequency division function of high pass, low-pass, or band-pass filters, the same antenna or transmission line can be used for two signal paths, thereby achieving the reception and transmission of two different frequency signals by the same antenna. In the figure below, signal A with frequency A enters the duplexer and passes through filter A to reach the antenna. The signal B with frequency B reaches the same antenna through filter B. The frequencies of these two signals need to be significantly different so that the filter can easily classify them.

　　According to different purposes, duplexers can also be made into triplets, multiplexers, etc.

　　Ringer is also a three port device, which is a three port or multi port device that transmits the incident wave entering any of its ports in the direction determined by the static bias magnetic field to the next port in sequence. Its significant feature is the ability to transmit high-frequency signal energy unidirectionally. It is divided into micro optical fibers and electronic circulators, and has good applications in isolators, duplexers, and reflection amplifiers.

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