I. Introduction

The measurement standards Center of Agilent Technologies International Japan, Ltd., has been calibrating a commercial four-terminal-pair (4TP) capacitance standard set at frequencies of up to 13 MHz using the Z-matrix method [1]. This method requires only one-port measurements using a vector network analyzer. The network analyzer is well designed to measure impedances of about 50 . Since the impedance of small capacitances at about 10 MHz is far greater than 50 , the small capacitance measurement suffers from insufficient signal-to-noise ratio . The main cause of result dispersion in high-impedance measurements is the discrepancy between the impedance values of a measured item and the reference impedance of the analyzer, i.e., 50 . Therefore, this method requires measurements at frequencies of greater than 13 MHz and the use of an interpolation method [2] by using an equivalent circuit [3] to reduce noise effects. Some institutes have reported improved using two-port measurements with an S-matrix model that is derived from the Z-matrix [4], [5]. Some others have reported measuring the 4TP standards using a high-frequency 4TP bridge [6]. A new short-bar method described in this paper can be used to calibrate standards with better using only one-port measurements at the nominal calibration frequency [7]. This paper also reports that the method in [1] and the new method are in good agreement. This is applicable to ISO 17025 5.4.5.2 Note 2, which requires the comparison of results using another method.