Design of an Ultrawideband Air-Filled Grounded Coplanar Waveguide for Near-Field Probe Calibration

This article proposes a novel air-filled grounded coplanar waveguide (AGCPW) structure for calibrating near-field probes. The structure uses a grounded coplanar waveguide (GCPW) with a cutout ground as the connector taper part to achieve a smoother impedance transition. Additionally, an AGCPW capable of exciting high-purity TEM fields serves as the probe calibration region. The designed cutout ground structure ensures good impedance control for the AGCPW, while a dual-row staggered via array suppresses high-order modes and resonance in the frequency range of 9 kHz-40 GHz. Subsequently, the field characteristics above the AGCPW structure are analyzed, revealing an undesired electric-field rejection ratio (UERR) and an undesired magnetic-field rejection ratio (UMRR) of 36 and 26.5 dB. Applying AGCPW to calibrate an H-field probe with a four-layer PCB structure, the results show that, compared to using other structures, AGCPW yields a smoother and more stable probe calibration factor (CF) and more accurate electric-field rejection ratio (ERR) results.