LRL/LRM modifications for sinlified high frequency multiport/differential measurements

Martens, J.; Judge, D.; Bigelow, J.

doi:10.1109/arftgf.2004.1427589

Cited by 1 publication

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“…in some contexts (e.g., [5]), this paper will focus more on detailed impacts to error terms and how these can be used to predict measured behavior. The issue can become even more convoluted in multiport systems (e.g., [6]- [7]) where LRM can be hybridized with other calibration techniques.…”

Section: Introductionmentioning

confidence: 99%

LRM: A quantitative look at reference impedance contradictions and other uncertainty impacts

Martens¹

2007

2007 69th ARFTG Conference

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As might be expected, directivity is not impacted since it is largely set by the match measurements. Tracking and source match are, however, affected with source match being far more sensitive. Starting with some typical VNA error coefficients, a 40 ohm line impedance in a 50 ohm Zref (I>-.11, admittedly a very large deviation) causes a tracking deviation of only~2.5% while source match deviates by more than 50% in terms of magnitudes (see Fig. 1). The angular deviations show a similar behavior. The relative errors in transmission tracking (el2l) are identical to those in reflection tracking (etl I).analysis is consistent with on-wafer measurements although the results are not restricted to that situation.One may ask about the situation where the loads and line impedance are both deviant from the reference impedance and are at the same value. This is a classical reference impedance renormalization problem (e.g., [8]-[9]) and will not be covered here. It should be noted that this renormalization only works if it is the line impedance that is deviant and not a situation where the line mismatch is created by bulk reflections (e.g., at launch points). In this case, the effective line impedance is deviant but with some frequency dependence. II. LINE IMPEDANCE DEVIATIONConsider the case where the loads are precisely known but the line characteristic impedance is deviant. As hinted at earlier, an internal contradiction has been created within the error terms: directivity referenced to Zref, other terms partially referenced to the line impedance. As a result, an impedance transformation cannot be easily used.There are a number of ways one could present the dependence, but the variation most closely obeys an artificial reflection coefficient between the line impedance and the reference impedance Zref. The reader may recognize this term as central to the usual impedance transformation equations [8].Abstract -LRM and its derivatives have been popular VNA calibration techniques, particularly on-wafer, for many years. The quantitative effects of standards problems (line impedance issues, match issues, reflect asymmetries) have not always been well-understood including the cases where the standards present internal contradictions to the calibration. These effects will be studied here through the use of constructed measurements and simulations based on a parameter space consistent with commercial VNAs and common test situations.

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Section: Introductionmentioning

confidence: 99%