An Ultrawideband Asymmetric Calibration Method for a Simultaneously Electromagnetic Near-Field Probing System

Calibration for asymmetry of the simultaneously electromagnetic near-field probing system is a good way of improving the performance of a two-port probe. The previous rotating asymmetric calibration method (RACM) based on microstrip line measurements at two directions of 0° and 90° is limited to 12 GHz. In this article, a nonrotating asymmetric calibration method (NRACM) is proposed for ultrawideband calibration of a simultaneously near-field probing system. A four-port vector network analyzer and a highly symmetric grounded coplanar waveguide (GCPW) calibrator are used to solve the calibration matrix in the proposed method. It only needs to place the probe at one direction of 0° instead of measurements at two directions and uses the time-domain reflectometry (TDR) for localization of the probe loop. These simplified measurement steps in the proposed method reduce the impact of positioning error. The non-TEM effect is automatically avoided because of no 90° measurement. A highly symmetric ultrawideband GCPW calibrator without soldering is adopted to excite standard electromagnetic fields for calibration. The measurement results of standing waves demonstrate that the proposed method is suitable for asymmetric calibration at a frequency as high as 20 GHz.

I. Introduction

Near-field measurement technique is promising for electromagnetic interference (EMI) diagnosis, assessment, and failure location in recent years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], with the trends of miniaturization and high frequency of electronic devices. The near-field probe based on the principle of electromagnetic induction is a simple, practical, and important tool for near-field diagnosis. There are several kinds of near-field probes, including vertical electric field (E-field) probe [11], [12], [13], [14], horizontal magnetic field (H-field) probe [14], [15], [16], and electromagnetic field (EM-field) probe [17], [18], [19], [20]. In 2019, a type of the EM-field probe (labeled as dual-probe) with a half unshielded loop structure is proposed by our team for simultaneous vertical E-field and horizontal H-field measurement at the same location [19]. It has the advantage of high efficiency in near-field detection and large scale mini-step near-field diagnosis and analysis.