Editing Circulator (section)

====Self-biased junction circulators====

[[File:Self-Biased Circulator 2a.jpg|thumb|100px|Self-biased junction circulator.]]

Self-biased junction circulators are unique in that they do not utilize permanent magnets that are separate from the microwave ferrite.  The elimination of external magnets significantly reduces the size and weight of the circulator compared to electrically-equivalent microstrip junction circulators for similar applications.

Monolithic ferrites that are used for self-biased circulators are M-type [[uniaxial]] (single magnetic axis) [[hexagonal ferrite]]s<ref name="Zeina, How, et al.">{{cite journal|title=Self-Biasing Circulators Operating at K<sub>A</sub>-Band Utilizing M-Type Hexagonal Ferrites|journal=IEEE Transactions on Magnetics|date=September 1992|issn=0018-9464|pages=3219–3221|volume=28|number=5|doi=10.1109/20.179764|first1=N.|last1=Zeina|first2=H.|last2=How|display-authors=etal}}</ref> that have been optimized to have low microwave losses.  In contrast with the [[magnetically soft]] (low-[[coercivity]]) ferrites used in other circulators, the hexagonal ferrites used for self-biased circulators are [[magnetically hard]] (high-[[coercivity]]) materials.  These ferrites are essentially ceramic permanent magnets.  In addition to their high [[magnetic remanence]], these ferrites have very large [[magnetic anisotropy]] fields, enabling circulator operation up to high microwave frequencies.<ref name="Geiler and Harris">{{cite journal|title=Atom Magnetism: Ferrite Circulators - Past, Present, and Future|journal=IEEE Microwave Magazine|date=September–October 2014|issn=1527-3342|pages=66–72|volume=15|number=6|doi=10.1109/mmm.2014.2332411|first1=Anton|last1=Geiler|first2=Vince|last2=Harris|s2cid=46417910 }}</ref>

Because of their thin, planar shape, self-biased circulators can be conveniently integrated with other planar circuitry.  Integration of self-biased circulators with semiconductor wafers has been demonstrated at [[Ka-band|K<sub>A</sub>-band]] and [[V-band]] frequencies.<ref name="Cui, Chen, et al.">{{cite conference|title=Monolithically Integrated Self-Biased Circulator for mmWave T/R MMIC Applications|first1=Yongjie|last1=Cui|first2=Hung-Yu|last2=Chen|display-authors=etal|date=December 2021|pages=4.2.1–4.2.4|location=San Francisco, CA, USA|conference= 2021 IEEE International Electron Devices Meeting (IEDM)|doi=10.1109/IEDM19574.2021}}</ref>