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一种可以在1.25MHz频率上高精度测量6dB增量衰减的系统已经研制成功,初步实验表明:系统误差的典型值为5μB(1μB=0.00001dB),分辨度为1μB。NBS制造的以调谐的线性混合头及功率检测器组成的专用线性度测量系统(LMS)已用于确定1.25MHz功率检测器的非线性。检测器是一个带有热隔离的珠状单热敏电阻,它可近似地线性跟踪输入功率的4:1的变化。非线性修正值是由线性度测量系统确定的,现在所用检测器的修正值为13μB左右。这个已校准的检测器及另一个同类的检测器被用于衰减测量系统(AMS)作功率比测量,以便测出被测件的衰减变化。预期起始插损可达100dB,测量6dB左右的变化量时,其准确度为0.001dB。对用于校准系统的元件都必须进行专门的设计考虑,以便使失配误差减小到不致使上述估计的准确度明显下降。
A system that can measure 6dB incremental attenuation with high accuracy at 1.25MHz has been developed. Preliminary experiments show that the typical system error is 5μB (1μB = 0.00001dB) with a resolution of 1μB. A dedicated linearity measurement system (LMS) made by NBS with a tuned linear mixing head and power detector has been used to determine the non-linearity of the 1.25MHz power detector. The detector is a bead thermistor with thermal isolation that approximates linearly the 4: 1 variation of the input power. The non-linear correction value is determined by the linearity measurement system. Now the correction value of the detector used is about 13μB. The calibrated detector and another detector of the same type are used for the power ratio measurement of the Attenuation Measurement System (AMS) to measure the change in attenuation of the DUT. Expected initial insertion loss up to 100dB, measuring about 6dB change, the accuracy of 0.001dB. Special consideration has to be given to the components used to calibrate the system in order to reduce the mismatch error to such an extent that the accuracy of the above estimation is not significantly reduced.