非理想校准件对S参数测量结果的影响

Influence of Non-ideal Calibration Elements on S-Parameter Measurements

TRL校准方法是矢量网络分析仪(Vector Network Analyzer,VNA)校准的常用方法之一,它通过对直通件、反射件和传输线3个标准件的测量,经过一系列计算获取各误差项的值。但是在实际测量中,这些校准件并不能在整个频带范围内具有理想的特性,从而在实际测量时会引起被测件S参数的测量不确定度。对于使用日益广泛的多端口VNA而言,测量不确定度的分析比二端口VNA更为复杂,目前对其开展的研究还不够广泛深入。文章以四端口VNA为例,对TRL校准过程中由非理想标准件引起的被测件的S参数测量不确定度进行研究。首先,运用广义节点的思想将四端口VNA的S参数测量不确定度用矩阵形式表示,再运用广义TRL校准方法,求得各误差项及其偏移的值,最终求得灵敏度系数的解析式,它可以对四端口VNA进行S参数测量不确定度的B类评估。

TRL calibration, one of the most commonly used calibration method, is to calibrate the VNA by measuring three standards through （T）, reflect （R） and line （L）. In practical applications, the calibration standards are not ideal in performance. Such non-ideal calibration elements will lead to deviations of error terms and, consequently, the uncertainty of measured S-parameter. As an example of multi-port VNA, the deviations of the measured S-parameters of 4-port VNA are presented as functions of the deviations of the calibration elements parameters from their ideal values. Using the concept of general node equation, a matrix formula for the S-parameter deviations with respect to the error terms has been deduced. In addition, expressions representing the deviations of error terms with respect to the non-ideal calibration standards are given by series of matrix operations. Finally, after calculation of sensitivity coefficients, they can be used for establishing the type-B uncertainty budget for S-parameter measurements.