Agilent Technologies 24A Guide de l'utilisateur télécharger pdf (Page 387)

100

101

7-42

Operating Concepts

Measurement Calibration

However, all of the incident signal does not always reach the unknown. Refer to Figure

7-26. 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 signal separation device and the measurement plane. The

vector sum of the leakage and the miscellaneous reﬂections is the effective directivity, E

Understandably, the measurement is distorted when the directivity signal combines

vectorally with the actual reﬂected signal from the unknown, S

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Figure 7-26 Effective Directivity E

Since the measurement system test port is never exactly the characteristic impedance

(50 ohms), some of the reﬂected signal bounces off the test port, or other impedance

transitions further down the line, and back to the unknown, adding to the original incident

signal (I). This effect causes the magnitude and phase of the incident signal to vary as a

function of S

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and frequency. Leveling the source to produce a constant incident signal

(I) reduces this error, but since the source cannot be exactly leveled at the test device

input, leveling cannot eliminate all power variations. This re-reﬂection effect and the

resultant incident power variation are caused by the source match error, E

as shown in

Figure 7-27.

Figure 7-27 Source Match E

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