Editing Circulator (section)

===Switching circulators===

[[File:Switching Circulator.jpg|thumb|200px|Internal construction of a WR-90 (WG 16; R 100) waveguide switching circulator.]]

Switching circulators are similar to other junction circulators, and their microwave theory of operation is the same, except that their direction of circulation can be electronically controlled.<ref name="Microwave Circulator Design" />

Junction circulators use permanent magnets to provide the static magnetic bias for the ferrite(s).  However, switching circulators typically rely on the [[remanent magnetization]] of the ferrite itself.  The ferrites that are used in switching circulators have square [[magnetic hysteresis]] loops and often sub-[[Oersted]] [[Coercivity|coercivities]].  Such a ferrite material requires a relatively small magnetic field and low energy level to flip its magnetic polarity.  This is distinctly advantageous for a switching circulator, but the absence of permanent magnets would be a disadvantage of a non-switching junction circulator that must retain its magnetic bias despite exposures to the potentially demagnetizing effects of stray magnetic fields, nearby ferrous materials, and temperature variations.

The magnetization polarity of the ferrite, and hence the direction of circulation of a switching circulator, is controlled using a magnetizing coil that loops through the ferrite.  The coil is connected to electronic driver circuitry<ref name="Helszajn Waveguide Junction Circulators" /> that sends current pulses of the correct polarity through the magnetizing coil to magnetize the ferrite in the polarity to provide the desired direction of circulation.