On my Keysight Impedance Analyzer, I am realizing measurement results which appear questionable. Can you explain?

The measurement results can often be improved with a simple modification in the type of correction applied by the instrument.

Figure 1 – Swept Impedance Response, Capacitor, [FIXED] Correction Points

Figure 1 is a plot of a swept response of a capacitor. Near the resonance frequency of approximately 220 KHz observe the undershoot and overshoot of the phase response (turquoise curve). The corrupted response is typically an artifact due to the default setting of [FIXED] correction points. The [FIXED] correction mode forces calibration and / or compensation to be executed at preset frequency points (instrument dependent). These preset frequency points may or may not correspond to the desired measurement points. The [FIXED] correction points mode results in interpolation of the correction data at the measurement frequency points.

The remedy is to override the [FIXED] correction points with [USER] correction points. [USER] correction ensures that calibration and / or compensation corrections are executed at the same frequency points as the measurements points. Figure 2 represents the same setup and DUT as indicated in Figure 1 except for the selection of [USER] versus [FIXED] correction prior to calibration and / or compensation.

Figure 2 – Swept Impedance Response, Capacitor, [USER] Correction Points

Summary:

[FIXED] correction points provide the user with the flexibility of modifying the instrument stimulus (start frequency, stop frequency, number of points, etc.) without the need for re-calibration and/or re-compensation. However, the [FIXED] correction may impair test result due to the resulting error correction interpolation.

[FIXED] correction test results are often degraded for devices which have rapidly changing frequency responses. [USER] correction mode allows for precise calibration and / or compensation at the actual measurement points. Within the [USER] mode measurement results are not interpolated.