Agilent Technologies 24A Guide de l'utilisateur télécharger pdf (Page 415)

7-70

Operating Concepts

TRL*/LRM* Calibration (ES Models Only)

Improving Raw Source Match and Load Match for TRL*/LRM*

Calibration

A technique that can be used to improve the raw test port mismatch is to add high quality

ﬁxed attenuators. The effective match of the system is improved because the ﬁxed

attenuators usually have a return loss that is better than that of the network analyzer.

Additionally, the attenuators provide some isolation of reﬂected signals. The attenuators

also help to minimize the difference between the port source match and load match,

making the error terms more equivalent.

With the attenuators in place, the effective port match of the system is improved so that

the mismatch of the ﬁxture transition itself dominates the measurement errors after a

calibration.

Figure 7-45 Typical Measurement Set up

If the device measurement requires bias, it will be necessary to add external bias tees

between the ﬁxed attenuators and the ﬁxture. The internal bias tees of the analyzer will

not pass the bias properly through the external ﬁxed attenuators. Be sure to calibrate with

the external bias tees in place (no bias applied during calibration) to remove their effect

from the measurement.

Because the bias tees must be placed after the attenuators, they essentially become part of

the ﬁxture. Their mismatch effects are the same for source match and load match, so the

TRL CAL routine will correct for their effects. Although the ﬁxed attenuators improve the

raw mismatch of the network analyzer system, they also degrade the overall measurement

dynamic range.

This effective mismatch of the system after calibration has the biggest effect on reﬂection

measurements of highly reﬂective devices. Likewise, for well matched devices, the effects

of mismatch are negligible. This can be shown by the following approximation:

Reﬂection magnitude uncertainty = E

+ E

)

+ E

1 2 ... 410 411 412 413 414 415 416 417 418 419 420 ... 452 453

Pas de commentaire

Agilent Technologies 24A Guide de l'utilisateur Page 415