TABLE OF CONTENTS Section 4.2 discussed the directional coupler, a component that has directional properties and no dc connection. The coupling takes place across a gap between the transmission lines, and the directional property comes about because of the length of the coupling area. This section discusses components that also have directional properties, but this time they have complete dc continuity. These components are the circulator and the isolator (the isolator is a special case of a circulator).
The directional property of the coupler comes about by the use of specific-length transmission lines, resulting in the device exhibiting a quarter-wave response at the appropriate frequency. With the circulator, there is an interaction between a magnetic field and a ferrite device that causes a gyromagnetic motion and results in highly directional properties for the component. To understand this gyromagnetic motion, think of a pail of water into which you place a paddle and begin stirring in a clockwise direction. If you drop some wood chips into the pail as you continue to stir, you will notice that the wood chips easily follow the circular motion of the water in the clockwise direction. Now imagine that you want some wood chips to go in a counterclockwise direction. You would readily see that that would be impossible because the water motion is too strong in the clockwise direction. The same thing occurs with a gyromagnetic motion in a circulator. The interaction of a magnetic field and the ferrite material inside the circulator...
