A Wideband Tangential Electric Field Probe and a New Calibration Kit for Near-Field Measurements

A wideband tangential electric field ( $E$ -field) probe with operating frequency of 4–15 GHz is proposed. The $E$ -field probe is designed on a four-layer printed circuit board (PCB) with high-performance Rogers substrate. A wideband balun based on a microstrip-to-slotline transition structure is integrated into the probe to realize balanced–unbalanced transform in a wide frequency band through field conversion. Numerical simulations show that the magnitude imbalance and the phase imbalance of the balun are below 1 dB and 1^°, respectively. To reduce the interference of the normal $E$ -field component to the calibration result, the slotline is used as a calibration kit to generate the standard field because of its excellent field distribution characteristics. The tangential $E$ -field probe placed at the center of a slotline for calibration captures the symmetrical $E$ -field, while the normal component regarded as interference can be suppressed by the wideband balun. The performance of proposed probe is demonstrated with simulation and laboratory experiments.

I. Introduction

In recent years, as the density of integrated circuits (ICs) increases with the increasing circuits’ operation frequency [1], near-field measurement technology has been highly valued by engineers and researchers because of its low cost, rapid measurement, and accuracy. Electromagnetic interference (EMI) produced by high-speed ICs and printed circuit boards (PCBs) can be effectively located by near-field scanning [2], [3]. Meanwhile, according to the near-field to far-field transformation theory, the far-field distribution can be obtained by near-field measurement [2]. Compared with expensive microwave anechoic chambers, near-field scanners effectively reduce cost, site area, and equipment. Hence, as the key elements of the near-field measurement system, near-field probes, including electric and magnetic probes, with good frequency response and anti-interference ability must be developed.