Variance Distribution of Reflection Coefficients in Six-Port Reflectometer

Toshiyuki YAKABE
Hatsuo YABE

IEICE TRANSACTIONS on Electronics   Vol.E77-C    No.6    pp.930-934
Publication Date: 1994/06/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Measurement Techniques for Microwave/Millimeter Wave)
six-port,  reflectometer,  random error,  

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This paper discusses the effect of random errors in power meter readings by the six-port reflectometer. By means of six-port techniques, the determination of the reflection coefficient (Γ) of a divice under test is reduced to the problem of finding a common intersection of three circles in the complex plane. Since the intersection usually forms a cluster due to the effect of measurement error, the extraction of a single value from the cluster including the radical center of the three circles is required. Two types of methods are presented for determining Γ. One uses a linear solution for the radical center, and the other is a statistically based nonlinear solution. In order to improve measurement accuracy, the effect of random errors in the sidearm power meter readings and due to the influence of the q-point locations are investigated for each method. By adding a random variation of 0.5% onto each of the three port power ratios, the variance distributions of Γ over the entire area of the Smith chart are simulated for comparison of these two solutions. The three dimensional variance distribution chart reveals that only the nonlinear solution suffers a variance increase shown as a ridgelike peak along the lines of centers of the three circles. As a result of computer simulations, it is clarified that the reflectometer has the property of measurement accuracy dependence on the value of Γ. A new type of six-port model is suggested, which is unlikely to be affected by random errors in the nonlinear solution.