Characteristics of RF Isolators

　　The prominent feature of an isolator is the unidirectional transmission of high-frequency signal energy, which controls the transmission of electromagnetic waves in a certain direction. The characteristic of unidirectional transmission of high-frequency signal energy is commonly used in microwave signal transmission systems, especially in the output stage of power amplifiers, to prevent the influence of excessive reflected signals at the device output end on the front-end.

　　Isolators are anisotropic microwave passive devices made of ferrite. Ferrite is a black brown ceramic originally named after the presence of iron oxides in it. When electromagnetic waves of microwave frequency pass through ferrite, the conductivity loss is very small. More importantly, it is a nonlinear anisotropic magnetic substance, and its magnetic permeability varies with an external magnetic field, exhibiting nonlinearity; After adding a constant magnetic field, its magnetic permeability to the microwave magnetic field is different in all directions, which means it has anisotropy. Due to this anisotropy, when electromagnetic waves pass through magnetized ferrite from different directions, they exhibit a non reciprocity. By utilizing this effect, various microwave ferrite components can be made, with the most commonly used being isolators and circulators.

　　Inserting an isolator between the signal source and the device under test can not only improve the impedance matching between the signal source and the device under test, but also prevent the reflected power generated by the device under test from entering the signal source.

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