What is the waveguide circulator design?

Waveguide circulator design principle:

The basic design idea of the conventional waveguide circulator is to apply a vertical stable external magnetic field to the gyromagnetic ferrite material built in the cavity, so that the propagation direction of the microwave signal is deflected when it passes through the ferrite area, thereby realizing the circular transmission of the signal Function.

The basic principle of the circulator:

The circulator is a special device made of microwave ferrite material, which can be made into a coaxial structure or a waveguide structure. Among them, the microstrip three-terminal circulator is the most widely used, using ferrite material as the medium, with a conduction band structure on it, and adding a constant magnetic field, it has circular characteristics. If you change the direction of the bias magnetic field, the direction of the loop changes.

Features of the circulator:

The outstanding feature of the circulator is the unidirectional transmission of high-frequency signal energy, which controls the transmission of electromagnetic waves in a certain direction, mostly used between the output end of the high-frequency power amplifier and the load, playing their own independent and "isolated" role. The load impedance does not affect the operating state of the amplifier in the event of a change or even an open or short circuit, thus protecting the power amplifier. The circulator has the characteristics of small size, frequency bandwidth and small insertion loss.

Application of circulator:

01. Isolators

When one port of the three-port ring is terminated at a matched load, it can be used as an isolator because the signal can travel in only one direction between the remaining ports. Isolators are used to shield devices on their input side from conditions on their output side; For example, to prevent microwave sources from being detuned by mismatched loads.

02. Duplexer

In radar, a circulator is used as a type of duplexer to route signals from the transmitter to the antenna and from the antenna to the receiver, without allowing the signal to reach the receiver directly from the transmitter. An alternative type of duplexer is a transmit-receive switch (TR switch) that alternates between the antenna and the transmitter and receiver.

In the next generation of cellular communications, people tend to favor full-duplex radios because it can send and receive signals simultaneously at the same frequency. Given today's limited, congested spectrum resources, full-duplex can directly benefit twice the data input and output speeds of wireless communications. Wireless communication is still performed using "half-duplex", sending or receiving signals at different time frames, and if at the same frequency (usually in radar), simultaneously sending and receiving signals at different frequencies (implemented by a set of filters called duplexers).

03. Reflection amplifier

A reflection amplifier is a microwave amplifier circuit that utilizes negative differential resistance diodes such as tunnel diodes and Geng diodes. Negative differential resistor diodes amplify signals and typically perform better than two-port devices at microwave frequencies. However, because diodes are single-port (two-terminal) devices, non-reciprocal components are required to separate the output amplified signal from the input-input signal. By using a 3-port circulator with a signal input connected to one port, a bias diode connected to the second, and connected to the third output load, the output and input can be disconnected.

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