A Middle Underfill L-Standard Design for Highly Impedance Continuity in Four-Port Probe De-Embedding Calibration

The calibration of the four-port three-component probe, measuring ${H}_{x}$ , ${H}_{y}$ , and ${E}_{z}$ , is interesting for near-field measurement. At high frequency, calibration errors caused by the frequency response are very distressing. These error reasons include the multiple refection caused by embedded part of the calibrator (first error term) and the single reflection caused by the probe approaching the calibrator (second error term). The first error term has been proven to be eliminated through de-embedding calibration method of two-port probe. However, the second error term cannot be removed by this method, which will cause the impedance discontinuity of calibration process. In this article, a middle underfill L-standard as a calibrator is proposed for a four-port three-component probe de-embedding calibration. The new L-standard design can increase the inductive reactance of transmission structure to resist the capacitive effect of the probe when approaching the calibrator. The results of simulation or measurement show that the new L-standard can improve the impedance continuity by nearly 75.6% with a suitable height. Compared with traditional embedding calibration method of four-port three-component probe, the frequency response after using the new calibrator can improve about $0.7\sim 2.2$ dB, and the ripples caused by embedded part can be eliminated.