Attenuation at Mixer Ports

Mismatch between the instruments, cables, and mixer introduces errors in the measurement that you cannot remove with a frequency response calibration. You can reduce the mismatch by using high quality attenuators as close to the mixer under test as possible.

When characterizing linear devices, you can use vector accuracy enhancement (measurement calibration) to mathematically remove all systematic errors from the measurement, including source and load mismatches. This is not possible when the device you are characterizing is a mixer operating over multiple frequency ranges: therefore, source and load mismatches are not corrected for and will add to overall measurement uncertainty.

To reduce the measurement errors associated with the interaction between mixer port matches and system port matches, you can place attenuators at all of the mixer’s ports. Figure 6-89 shows a plot of swept conversion loss where no attenuation at mixer ports was used. The ripple versus frequency is due to source and load mismatches+

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Figure 6-89.

Conversion Loss versus Output Frequency Without Attenuators at

Mixer Ports

In contrast, Figure 6-91 made use of appropriate attenuation at all mixer ports You should give extra care to the selection of the attenuator located at the mixer’s IF port to avoid overdriving the receiver. For best results, choose the value of this attenuator so #at the power incident on the analyzer’s R channel port is less than -10 dBm and greater than -35 dRm.

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HP 8753E manual Attenuation at Mixer Ports