Time : 2016-09-02
Circulator is used to transmit the incident wave which entry from any port of its body to the next port, according to a certain direction confirmed by Static bias magnetic field. It is a nonreciprocal devices with sevral ports. For example, input signal from port 1, the signal can just output from port 2, the same princple, input signal from port 2, the signal can just output from port 3. By parity of reasoning, it is called circulator. Circulator is also called Isolator for the outstanding feature that it can transmit high frequency signal energy in one way. It controls the electromagnetic wave transmission along a circular direction. The characteristics that transmitting high frequency signal energy in one way is often used between output and load of the high frequency power amplifier, playing a part in isolating them from each other. Load impedance will not influence the amplifier when it is changing or even open-circuited or short-circuited.
The princple of circulator’s one-way transmission, is due to the adoption of ferrite gyromagnetic material. This material will produce gyromagnetic features (also called tensor permeability features) if it is under the combined action of high frequency wave field and constant dc magnetic field. This gyromagnetic features, making the electromagnetic wave which is transmitting through ferrite occurs polarized rotation(called as Faraday effect), and strong absorption of electromagnetic energy (ferromagnetic resonance). People manufactures Isolator and Circulator by making use of this gyromagnetic phenomenon. They has small volume, wide band, low insertion loss, etc, and thus the application is very extensive.