Editing Circulator (section)

{{short description|Electronic circuit in which a signal entering any port exits at the next port}}
<!-- {{other uses}} -->
{{About|radio frequency (RF) or microwave frequency passive circulators|other uses|Circulator (disambiguation)}}

[[File:Circulator-symbol-CCW.svg|thumb|[[ANSI]] and [[International Electrotechnical Commission|IEC]] standard [[electronic symbol|schematic symbol]] for a circulator (with each waveguide or transmission line port drawn as a single line, rather than as a pair of conductors)]]<!-- although it says ''optical circulator'', this symbol is also used at RF and microwave frequencies -->

In [[electrical engineering]], a '''circulator''' is a [[passivity (engineering)|passive]], non-[[Reciprocity (electrical networks)|reciprocal]] three- or four-[[port (circuit theory)|port]] device that only allows a [[microwave]] or [[radio frequency|radio-frequency]] (RF) signal to exit through the port directly after the one it entered. [[Optical circulator]]s have similar behavior. Ports are where an external [[waveguide (electromagnetism)|waveguide]] or [[transmission line]], such as a [[microstrip]] line or a [[coaxial cable]], connects to the device. For a three-port circulator, a signal applied to port 1 only comes out of port 2; a signal applied to port 2 only comes out of port 3; a signal applied to port 3 only comes out of port 1. An ideal three-port circulator thus has the following [[scattering parameters|scattering matrix]]:

:<math>S = \begin{pmatrix}
  0 & 0 & 1\\
  1 & 0 & 0 \\
  0 & 1 & 0
\end{pmatrix}</math>