Yttrium iron garnet filter

Yttrium iron garnet filter (YIG filter, YIGF) is a tunable electronic filter for microwave frequencies. It typically has a high Q factor.

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YIG filter uses a synthetic single crystal yttrium iron garnet sphere acting as a resonator. The garnet sits on a strip of metal driven by a transistor, and a small loop antenna almost touches the top of the sphere. An electromagnet changes the frequency that the garnet will pass. The advantage of this method is that the garnet can be tuned over a very wide frequency by varying the strength of the magnetic field; some filters can be tuned between 2GHz to 8 GHz.

The input and output coils are orientated at right angles to one another around the YIG crystal. They are cross-coupled when energised by the electron spin precession frequency, which depends on the external magnetic field, supplied by an electromagnet.

YIG filters are often used as preselectors. YIG filters tuned by a sweep voltage are used in spectrum analyzers.

A modified version acting as a tunable oscillator is the YIG oscillator.