Study of Fields Above Differential Microstrip lines for Probe Characterization Application

The spatial resolution of probe is defined for a 6-dB level drop point from the peak point close to the edge of the microstrip line. However, this definition is not clear for strongly coupled traces. If the spacing between adjacent traces is small enough, the probe may not detect multiple sources. In this paper, near fields above differential microstrip lines are investigated numerically and theoretically for probe characterization of spatial resolution. Results show several limiting cases for the probe to discriminate two RF sources in close proximity. It is discovered that two traces can be easily distinguished with differential mode excitation, while the detection for the common mode excitation cases is affected by probe height and trace spacing.