This work proposes an improved technique for accurate, contactless measurement of the absolute voltage waveforms of microwave circuits, employing a passive electric-field sensing probe. The proposed technique uses an electromagnetic model of the interaction between the probe and a device under test, to allow the extraction of the coupling capacitance variation versus frequency. Employing these information the measurement accuracy is improved, especially for higher (i.e., harmonic) frequencies, yielding enhanced waveform fidelity. The proposed method is validated on a microstrip line carrying waveforms with rich harmonic content. The accuracy of the proposed technique is benchmarked against a conventional thru-reflect-line (TRL) de-embedding approach by a nonlinear vector network analyzer (NVNA). Measurement results show that the root-mean square (RMS) error can be improved by 3 percentage points (from 8% to 5%) compared to the prior arts over the frequency range from 1 to 5 GHz.
- nonlinear vector network analyzer (NVNA)
- electric-field probe
- microwave circuit testing