The function and principle of a circular device

　　The function of a roundabout is to transmit the incident wave entering any of its ports in the direction determined by the static bias magnetic field to the next port in sequence. A cyclist is a non reversible device with multiple ends. For example, if a signal is input from port 1, it can only be output from port 2. Similarly, if a signal is input from port 2, it can only be output from port 3, and so on. Therefore, it is called a loopback. The prominent feature of a roundabout, also known as an isolator, is the unidirectional transmission of high-frequency signal energy. It controls the transmission of electromagnetic waves along a certain circular direction. The characteristic of unidirectional transmission of high-frequency signal energy is often used between the output terminal of high-frequency power amplifiers and the load, playing an independent and mutually "isolated" role. The load impedance does not affect the working state of the power amplifier even in the case of changes or open or short circuits, thus protecting the power amplifier.

　　The principle of unidirectional transmission in a circular device is to utilize the characteristics of ferrite ferromagnetic materials. This material exhibits rotational magnetic properties (also known as tensor permeability) under the combined action of an external high-frequency wave field and a constant DC magnetic field. It is precisely this rotational magnetic property that causes polarized rotation of electromagnetic waves propagating in ferrite (Faraday effect), as well as strong absorption of electromagnetic wave energy (ferromagnetic resonance). By utilizing this rotational magnetic phenomenon, junction isolators and circulators are made. It has the characteristics of small size, wide bandwidth, and low insertion loss, so it is widely used.

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