Contents I. Introduction
Due to the rapid increase of operating frequency, the frequent switch of the high-speed system clock, the serious enhance of layout complexity, the decreasing compact size of printed circuit board (PCB), and the increasing use of radio frequency (RF) modules, new challenges are occurring in the design of the electromagnetic compatibility (EMC) for the RF systems [1]. Unwanted electromagnetic emissions radiated from the RF systems may be picked by the susceptible components, which will result in function failure and weaken the stability of the RF system. Near-field scanning point by point, combined with the near-field probes [2]–[8], is an effective diagnostic technique to access the unwanted emissions and track the coupling path of the noise [9]. However, such passive probes are not sensitive enough to effectively obtain the weak target noise signal. Especially, below 1 GHz the sensitivities of the passive probes in [2] and [4] are so low that external amplifiers are required in the measurements. Blindly enlarging the sensing loops of the passive magnetic field probes is not an optimized method to improve the sensitivity, since the sensitivity and the spatial resolution of the probe are compromising.
