Thursday
Jul152010

Ferrite Circulator

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This microwave circulator is a microstrip design with a 12 mm radius. The magnetized ferrite material has a biasing field of 300 Oe in the -z direction perpendicular to the circulator plane and a saturation magnetization of 300 Gauss. The three microstrip lines forming the ports are terminated with 120 ohm resistors which approximately match the characteristic impedance of the mcrostrip. Figure 1 shows the circulator mounted on a metal ground plane.

 

Figure 1
Ferrite circulator structure.

The circulator is excited at Port 1 with a broadband input. S-Parameters were collected from a simulation and can be observed in Figure 2. The plots of S11, S21, and S31 show the first resonance near 6.6 GHz. At this frequency, Port 2 is 10 dB smaller than Port 3 while Port 1 is matched.
 

Figure 2
Broadband S-Parameters showing the isolation at the receive ports.

Steady state electric fields were also collected at 6.6 GHz, as shown in Figure 3. The null at Port 2 can be seen and is due to the interfering waves traveling around the ferrite at different velocities.

 

Figure 3
Steady state electric field strength at 6.6 GHz.

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