A Contactless Method for Measuring Amplitude and Phase of RF Voltages up to 26.5 GHz

In this article, a method for contactless amplitude and phase measurements of local voltages within microwave devices is developed. A conductive cantilever probe with a sharp tip is used as capacitively coupled sensor to record radio frequency (RF) voltages at well-defined distances between the probe tip and the device surface. The recorded voltage is compared to a nonlinear capacitance versus distance model to separate the local voltage on the device from long-range crosstalk contributions. To determine both amplitude and phase of the local voltage, a complex parameter identification procedure is proposed and implemented. Thus, amplitude and phase measurements of local voltages at
$\mu \text{m}$
spatial resolution are enabled. Additionally, the cantilever probe is integrated on a PCB to enable the transmission of RF signals from the tip to the detector over a wide bandwidth. The proposed method, together with the developed probe, are verified by performing voltage measurements on an open-ended transmission line at frequencies from 1 to 26.5 GHz. The measurements closely match the analytically calculated standing wave patterns on the transmission line.