Agilent Technologies 24A Guia do Utilizador descarregar pdf (Página 392)

100

101

7-47

Operating Concepts

Measurement Calibration

Figure 7-34 Major Sources of Error

The transmission coefﬁcient is measured by taking the ratio of the incident signal (I) and

the transmitted signal (T). Refer to Figure 7-35. Ideally, (I) consists only of power delivered

by the source, and (T) consists only of power emerging at the test device output.

Figure 7-35 Transmission Coefﬁcient

As in the reﬂection model, source match can cause the incident signal to vary as a function

of test device S

11A

. Also, since the test setup transmission return port is never exactly the

characteristic impedance, some of the transmitted signal is reﬂected from the test set

port 2, and from other mismatches between the test device output and the receiver input,

to return to the test device. A portion of this signal may be re-reﬂected at port 2, thus

affecting S

21M

, or part may be transmitted through the device in the reverse direction to

appear at port 1, thus affecting S

11M

. This error term, which causes the magnitude and

phase of the transmitted signal to vary as a function of S

22A

, is called load match, E

. See

Figure 7-36.

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