Editing Circulator (section)

==Applications==

===Isolator===
When one port of a three-port circulator is terminated in a matched load, it can be used as an ''[[isolator (microwave)|isolator]]'', since a signal can travel in only one direction between the remaining ports.<ref name="Jachowski Patent">For a description of a circulator, see {{Harvtxt|Jachowski|1976}}</ref> An isolator is used to shield equipment on its input side from the effects of conditions on its output side; for example, to prevent a microwave source being detuned by a mismatched load.

===Duplexer===
In [[radar]], circulators are used as a type of [[duplexer]], to route signals from the [[transmitter]] to the [[antenna (radio)|antenna]] and from the antenna to the [[radio receiver|receiver]], without allowing signals to pass directly from transmitter to receiver. The alternative type of duplexer is a ''transmit-receive switch'' (''TR switch'') that alternates between connecting the antenna to the transmitter and to the receiver. The use of chirped pulses and a high dynamic range may lead to temporal overlap of the sent and received pulses, however, requiring a circulator for this function.

===Reflection amplifier===
[[File:Negative resistance amp.svg|thumb|Microwave diode reflection amplifier using a circulator]]
A [[reflection amplifier]] is a type of microwave amplifier circuit utilizing [[negative differential resistance]] diodes such as [[tunnel diode]]s and [[Gunn diode]]s. Negative differential resistance diodes can amplify signals, and often perform better at microwave frequencies than two-port devices.  However, since the diode is a one-port (two terminal) device, a nonreciprocal component is needed to separate the outgoing amplified signal from the incoming input signal. By using a 3-port circulator with the signal input connected to one port, the biased diode connected to a second, and the output load connected to the third, the output and input can be uncoupled.