Improved circuit for impedance measurement at very high frequency and its application in testing dielectric properties of insulating materials

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Abstract
This paper describes improvements on an impedance measuring circuit for the measurement of very small conductance at very high frequency and one of its applications, viz., the accurate measurement of dielectric constant and loss angle of very low loss materials. In this circuit, a feedback loop for the stabilization of the output level of the high‐frequency oscillator unit also provides compensation for the changes of the series resistance of resonance coil and the transfer characteristic of the detector that occur with their temperature drifts. This circuit has the sensitivity and stability to detect a 0.002 μmho change in a 16‐pF specimen at 100, 150, or 200 MHz. It is capable of measuring a loss angle of several μrad with the electrode system developed for the varying gap immersion method. The warming‐up time is also shortened to about 10 min even for measurements requiring the highest sensitivity.

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