Reflection type Q-factor measurement using standard least squares methods

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Reflection type Q-factor measurement using standard least squares methods

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© The Institution of Engineering and Technology
Published

Methods to determine resonant cavity Q-factor from vector network analyser reflection data are often quite complex. This study presents a simple method which makes use of two least squares algorithms applied sequentially. Firstly, a circle is fitted to the data, which is then projected onto a linear frequency scale using the Ginzton technique. A straight line is fitted to the projected data, and the loaded Q-factor and the resonant frequency are obtained from the line coefficients. The method has been tested on both synthetic and experimental data, and compared with the Kajfez QZERO software, and the results are shown to be accurate to a fraction of 1%.

Inspec keywords: least squares approximations; Q-factor measurement

Other keywords: Ginzton technique; least squares algorithm; reflection type Q-factor measurement; straight line; resonant frequency; loaded Q-factor; line coefficients; standard least squares method; resonant cavity Q-factor; Kajfez QZERO software; linear frequency scale; vector network analyser reflection data

Subjects: Interpolation and function approximation (numerical analysis); Other electric variables measurement

References

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      • R.S. Murray . (1972) Theory and problems of statistics.
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      • E.L. Ginzton . (1957) Microwave measurements.
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      • I. Kasa . A circle fitting procedure and its error analysis. IEEE Trans. Instrum. Meas. , 8 - 14
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      • D. Kajfez . (1994) Q-Factor.
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