Differential <inline-formula> <tex-math notation="LaTeX">$E$ </tex-math> </inline-formula>-Field Coupling to Shielded <inline-formula> <tex-math notation="LaTeX">$H$ </tex-math> </inline-formula>-Field Probe in Near-Field Measurements and a Suppression Approach

Abstract

In near-held scanning using H-held probes, E-held coupling is a major concern. E-held suppression performance must be characterized before an H-held probe can be used for near-held scanning. Common method of measurement involves measuring the E-held coupling in the same location where the strongest H-held coupling occurs. In microstrip line traces, it is assumed that this occurs right above the center of the trace and less coupling at all other locations across the microstrip line. In this paper, we show that the maximum E-held coupling occurs at a location slightly offset from the trace center. The E-held coupling to a shielded H-held probe at such a position leads to differential-mode coupling, which the standard shield of an H-held probe is unable to suppress. The coupling mechanism is investigated and a differential E-held coupling suppression approach is proposed. For the H-held probe used in this paper, a proposed floating plate is shown to improve the measured E-held suppression ratio by a factor of 18 dB compared to a similar probe without this modihcation.