Four-Port Asymmetric Correction for Simultaneous Multicomponent EM-Field Measurement

The electromagnetic field probing system with a multiport probe as a high-efficiency simultaneous multicomponent near-field emission measurement tool has been paid more attention. However, strict symmetry requirements of the electromagnetic near-field (EM-field) probing system limit its applications. In this article, a four-port asymmetric correction method (FPACM) is proven to be effective for an asymmetric cross-loop EM-field probing system. This method solves a more general asymmetric problem when a symmetric four-port probe connects to a four-port instrument through four asymmetric elements. In this method, the S-parameter of the symmetric four-port probe and four asymmetric elements must be known to establish the relationship between the measured EM-field components and the measurement voltages of the instrument. Typical measurement results of the calibration factor with and without the proposed method using an asymmetric four-port EM-field probing system prove the effectiveness of the proposed method. Compared with the original perfectly symmetric probing system, the ripple error of the calibration factor with the proposed method does not exceed 1.0 dB, and the amplitude error at 10 GHz is less than 3.2 dB. Meanwhile, the standing-wave field measurement results also verify the validity of the proposed method for the four-port asymmetric probing system, and the suppression ability of two horizontal magnetic fields can reach more than 17.7 dB within 20 GHz.