A Brief Analysis of Circular Isolators and RF Isolators

　　Circulators and isolators are both microwave ferrite devices that control the transmission of microwave signals through ferrite and rely on magnetic fields to complete non reciprocal work. Due to its non reciprocity, the forward insertion loss is very small, while in the reverse direction, the majority of the energy is absorbed. The microwave ferrite in the device determines its resonant frequency.

　　Non reciprocity is a term used in microwave technology and materials science, which refers to the phenomenon where electromagnetic waves exhibit different electromagnetic losses, phase shifts, and other characteristics when transmitted in opposite directions in an object. This phenomenon is called non reciprocity.

　　Circulator: A 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. The prominent feature is the unidirectional transmission of energy, which controls the transmission of electromagnetic waves along a certain circular direction. The signal can only go from port 1 to port 2, from port 2 to port 3, from port 3 to port 1, and all other paths are not connected (high isolation).

　　Circulators may use ribbon printed circuit board technology (but typically use very low loss dielectric or PCB materials) and are included in metal boxes with connectors or other external connections - some even use surface mount technology. Other circulators may be based on waveguides, which can be used for RF system design applications that combine waveguide technology.

　　It is worth noting that each port, whether it is a coaxial feeder or waveguide, is displayed as a single line rather than a pair of conductors. One of the commonly used forms of RF circulators is formed by the Y-shaped portion of microstrip or stripline transmission lines located on printed circuit boards or other dielectrics. Ports are placed 120 ° apart, so they are evenly spaced around a circle. The circulator does not operate at this frequency, but has greater losses above or below that frequency because the insertion loss, i.e. attenuation, is much lower in this frequency range.

　　Radio frequency circulator application: One of the most obvious and common applications of radio frequency circulators is in radar systems or radio communication systems, where the transmitter and receiver use a common antenna. For example, the transmitter output is connected to port 1, the antenna is connected to port 2, and the receiver is connected to port 3. The transmitter power will loop to the antenna instead of the receiver, and the signal received by the antenna will loop to the receiver. In this way, the receiver is isolated from the transmitter, but the antenna has power from the transmitter and transmits the received signal to the receiver without any mechanical switching.

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