The circulator also includes a magnet on top of the substrate over a resonator circuit part of the microstrip lines and a pole piece on the bottom of the substrate beneath {HEAD ~ the ground} for providing {TAIL ~ a magnetic field} in the substrate between the microstrip lines and the ground such that signals are coupled between the microstrip lines in a particular direction 
for providing
The circulator also includes a magnet on top of the substrate over a resonator circuit part of the microstrip lines and a pole piece on the bottom of the substrate beneath { HEAD ~ the ground } for providing { TAIL ~ a magnetic field } in the substrate between the microstrip lines and the ground such that signals are coupled between the microstrip lines in a particular direction
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