A Low-Cost and High-Flatness E-Field Probe Based on Fan-Shaped Tip and SCE Transition for Ultrawideband EMI Measurement

The demand for electric-field probes with high accuracy and low fabrication costs in ultrawideband electromagnetic interference (EMI) measurements is becoming increasingly imperative. In this paper, a low-cost ultrawideband E-field probe with enhanced gain flatness is proposed, fabricated and tested. Due to the low-cost FR-4 PCB stack-up, the fan-shaped tip and the symmetric chamfered edge (SCE), the proposed E-field probe maintains a high gain flatness in terms of |S₃₁| within 9 kHz-20 GHz while significantly decreasing the fabrication cost. The fan-shaped tip and the SCE are designed to improve the gain flatness by suppressing resonances and ripples of the frequency response (FR) for the proposed probe. Quasi Fast Fourier Transform (QFFT) and Feature Selective Validation (FSV) method are introduced and applied to provide a scientific and intuitive evaluation for the probe’s gain flatness. The measured |S₃₁| of the proposed probe exhibits an average fluctuation of less than 1.5 dB below 15 GHz. The calibration factor (CF) of the proposed E-field probe is calibrated by multiple methods, achieving superior flatness with a ripple factor of about 0.0026. The measured results demonstrate a maximum cross polarization difference of approximately 4.47 dB between θ=0° and θ=90° and a spatial resolution of 1 mm both at H=0.3 mm. EMI measurements on passive and active devices under test (DUTs) in real EMC scenarios are conducted to validate the robustness of the proposed E-field probe.