Editing Circulator (section)

===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.