Characterizing Microwave Systematic Errors

One-Port Error Model

In a measurement of the reflection coefficient (magnitude and phase) of a test device, the measured data differs from the actual, no matter how carefully the measurement is made. Directivity, source match, and reflection signal path frequency response (tracking) are the major sources of error (see Figure 6-32).

Measured

Data

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Figure 6-32. Sources of Error in a Reflection Measurement

lb characterize the errors, the reflection coefficient is measured by lirst separating the incident signal (I) from the reflected signal (R), then taking the ratio of the two values (see Figure 6-33). Ideally, (R) consists only of the signal reflected by the test device (&IA, for S11 actual).

s K

11M = f

.I

U n k n o w n

Figure 6-33. Reflection CoefHcient

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However, ail of the incident signal does not always reach the unknown (see Figure 6-34). Some of (I) may appear at the measurement system input due to leakage through the test set or through a signal separation device. Also, some of (I) may be reflected by imperfect adapters between a signaI separation device and the measurement plane. The vector sum of the leakage and the miscellaneous reflections is the effective directivity, Eur. Understandably, the measurement is distorted when the directivity signal combines vectorally with the actual reflected signal from the unknown, &A.

Application end Operation Conoepts 6-61

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HP 8753E manual Characterizing Microwave Systematic Errors, One-Port Error Model