Complex sentence: 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 from 3 GHz up to 50 GHz.
Split into simpler sentences: The advantage of this type of filter is that the garnet can be tuned over a very wide frequency range by varying the strength of the magnetic field. Some filters can be tuned from 3 GHz up to 50 GHz.