Similarly, finite isolation of directional couplers or bridges within the network analyzer results in a leakage term during reflection measurements called directivity. Signal leakage during transmission measurements is called crosstalk and is a result of finite isolation between the test ports. There are two error terms in each group for a total of six error terms. Systematic errors encountered in network measurements can be grouped in terms of signal leakage, signal reflections or frequency response. If these errors do not vary over time, they can be characterized through calibration and removed mathematically during the measurement process. Systematic errors, as shown in Figure 2, are caused by imperfections in the test equipment and test setup. Calibrations are also shown for those cases requiring coaxial adapters to connect the test equipment, DUT and calibration standards.Īll measurement systems, including those using network analyzers, can be affected by three types of measurement errors: systematic, random and drift. The effectiveness of these procedures is demonstrated in the measurement of high frequency components such as filters. This article describes several types of calibration procedures, including short-open-load-thru (SOLT) and thru-reflect-line (TRL). (Mismatch errors are those due to nonperfect 50 W source and load matches.) The smoother, error-corrected trace produced by a two-port calibration subtracts the effects of all major systematic errors and illustrates the performance of the device under test (DUT) accurately. However, considerable measurement ripple still exists due to mismatch errors. A simple error-correction technique such as response calibration removes the overall loss and frequency-response error. Without error correction, measurements on this example bandpass filter show considerable loss and ripple. The effect of error correction on data can be dramatic, as shown in Figure 1. Once these errors are characterized, they can be removed mathematically from subsequent measurements. Measurements of these standards provide knowledge about systematic errors in the test system. The process of network analyzer error correction is based on the measurement of known electrical standards, such as thru, open circuit, short circuit and precision-load impedance. Some factors that contribute to measurement errors are repeatable and predictable over time and temperature and can be removed, while other errors are random and cannot be removed. However, imperfections exist in even the finest test equipment and can cause less-than-ideal measurement results. Ideally, measurement systems would be perfect and provide completely accurate measurements. Vector network analysis is a method of characterizing components accurately by measuring their effect on the amplitude and phase of swept-frequency and swept-power test signals. When these devices convey signals with information content, designers and manufacturers are most concerned with moving the signal from one point to another in the device with maximum efficiency and minimum distortion. Applying Error Correction to Network Analyzer Measurementsĭesigners and manufacturers use network analysis to measure the electrical performance of the components and circuits destined for use in more complex systems.
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