Editing Circulator (section)

===Differential phase shift circulators===
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[[File:High-Power-DPS Circulator.jpg|center|500px|thumb|High-Power Liquid-Cooled Differential Phase Shift Circulator.  Image courtesy of [http://www.microwavetechniques.com Microwave Techniques]]]
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[[File:DPS Schematic.jpg|200px|thumb|Schematic diagram of a differential phase shift circulator.]]

[[File:Differential Phase Shifter Image.jpg|100px|thumb|Internal construction of a differential phase shifter.]]

Differential phase shift circulators are mainly used in high power microwave applications.  They are usually built from [[Waveguide (radio frequency)|rectangular waveguide]] components.  These circulators are 4-port devices having circulation in the sequence 1 - 2 - 3 - 4 - 1, with ports numbered as shown in the schematic.  There are various feasible circulator architectures, the most common of which utilizes a [[Magic tee|magic tee hybrid coupler]], a [[Power dividers and directional couplers|quadrature hybrid coupler]], and two oppositely-magnetized differential phase shifters.<ref name="Helszajn Microwave Ferrite Engineering">{{Cite book|title=Principles of Microwave Ferrite Engineering|first=Joseph|last=Helszajn|date=1969|publisher=John Wiley & Sons Ltd.|isbn=0-471-36930-6}}</ref>

A differential phase shifter provides ''non-reciprocal'' transmission phase shift.  That is, the forward phase shift is different from the phase shift in the reverse transmission direction.  It is this difference in phase shifts that enables the non-reciprocal behavior of the circulator.  A differential phase shifter consists of one or more ferrite slabs, usually positioned on the broad wall(s) of the waveguide.  Permanent magnets located outside the waveguide provide static magnetic bias field to the ferrite(s).  The ferrite-loaded waveguide is another example of a ''transverse-field'' device as described in {{slink|Circulator|Theory of operation}}.  Different microwave propagation constants corresponding to different directions of signal propagation give rise to different phase velocities and hence, different transmission phase shifts.

Depending on which circulator port an incident signal enters, phase shift relationships in the hybrid couplers and the differential phase shifts cause signals to combine at one other port and cancel at each of the remaining two ports.  Differential phase shift circulators are often used as 3-port circulators by connecting one circulator port to a reflectionless termination, or they can be used as isolators by terminating two circulator ports.

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[[File:S-Band Differential Phase Shift Circulator Animation.gif|center|600px|thumb|E-field animation of microwave signal propagation through a high-power S-band differential phase shift circulator.  In this animation, the signal propagating through the upper differential phase shifter is seen to have a higher velocity than the signal in the lower differential phase shifter.  Just before the signals reach the quadrature hybrid on the right, the upper signal leads the lower signal by about 90°.  Animation courtesy of [https://www.symphony-microwave.com Symphony Microwave Technologies]]]