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用同轴测量线测量阻抗已有几十年的历史。到目前为止,优质的同轴测量线剩余,驻波比可达1.01(在10GHz下),测量精度可达1％。但测量线有许多明显的缺点:只能窄带调谐,测量小驻波精度低,系统需调配,加工困难及操作麻烦等。六十年代出现了反射计,它在一定程度上克服了测量线的缺点,但仍有许多不足之处。如高方向性宽频带定向耦合器难于实现。此外,需对系统调配、测小驻波困难、加工困难等缺点依然存在。七十年代后期,美国Willtron公司打破常规,把低频电桥成功地应用于微波测量,而制成了一种反射电桥。这种电桥实现了高方向性、宽频带扫频测量,其频率范围可复盖100KHz至18GHz,测量小反射能力及测量精度都有了较大提高。本文拟介绍这一技术的原理,并提出若干改进测量精度的方法。
It has been decades to measure impedance using coaxial measuring lines. So far, the remaining coherent measurement lines with excellent VSWR of up to 1.01 (at 10 GHz) can achieve measurement accuracy of up to 1%. However, the measurement line has many obvious shortcomings: only narrow-band tuning, low-precision measurement of small standing waves, the system needs to be deployed, processing difficulties and operational troubles. Reflectometer appeared in the sixties, it overcomes the shortcomings of the measuring line to a certain extent, but there are still many shortcomings. Such as high-directional broadband directional coupler difficult to achieve. In addition, the system deployment, short test standing wave difficulties, processing difficulties and other shortcomings still exist. In the late seventies, the United States Willtron company to break the routine, the low frequency bridge successfully used in microwave measurements, and made a kind of reflective bridge. This bridge to achieve high directivity, wideband sweep measurement, the frequency range can cover 100KHz to 18GHz, the measurement of small reflectivity and measurement accuracy have been greatly improved. This article is intended to introduce the principles of this technique and propose several ways to improve the measurement accuracy.