Microwave Circulator Geometry uses anisotropic magnetized ferrite to isolate one port while providing output to the other. Views of the geometry and a plot of the object's S-parameters are shown.

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This example shows a microwave circulator that uses anisotropic magnetized ferrite to isolate one port while providing output to the other.The circulator is a microstrip design with a 12 mm radius. The ferrite has a biasing field of 300 Oe in the -z direction perpendicular to the circulator plane and a saturation magnetization of 300 Gauss. These correspond to Larmor Precession frequency of 5.275 E9 radians per second and a saturation magnetization also of 5.275 E9. The ferrite damping coefficient is 1.0E-4. XFdtd^® is one of very few electromagnetic analysis programs capable of making this calculation.

The three microstrip lines forming the ports are terminated with 120 ohm resistors which approximately match the characteristic impedances of the microstrip.The circulator is excited at port 1 with a voltage pulse. Comparing dB plots of S11, S21, and S31 shows that at about 6.5 GHz, S21 is about 10 dB smaller than S31 and S11 is matched. This is the first resonance of the circulator.

A second XFdtd calculation was made at a frequency of 6.5 GHz, the lowest resonance. The steady-state electric field in the ferrite shows the null at port 2 due to the interfering waves traveling around the ferrite atdifferent velocities.

Figure 1 shows a three-dimensional view of the circulator showing the ferrite disk below the circular microstrip.

Figure 2 shows a steady state electric field in the ferrite perpendicular to the plane of the circulator disk at 6.5 GHz.

Figure 3 is a graph of S parameters vs frequency from the transient XFdtd calculation.