An analysis of magnetic field sensing coil using microstrip line is presented. Broad-bandwidth magnetic sensor is built in which the characteristic impedance is determined to be 50Ω. We examined the coil size dependence for the output voltage and coil impedance as well as three dimensional ac field analysis. The output voltage of the coil is produced by a varying magnetic field linking the closed circuit loop which is composed of the microstrip conductor, 50Ω resistor, and the ground plane below radiation frequency. Eddy current generated in the ground plane decreases the output voltage of microstrip coil. Optimum design depends on the trade off between impedance matching and increase in output voltage.
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