volume | PIER Journals

2008-10-27

Applying Critical-Points Method in the Presence of Phase Shift Due to Feed Line

Changying Wu,

Dr. Changying Wu

Northwestern Polytechnical University

China

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Kai Zhang,

Dr. Kai Zhang

School of Electronics and Information

Northwestern Polytechnical University

China

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Gao Wei,

Dr. Gao Wei

School of Electronic and Information

Northwestern Polytechnical University

China

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Jia-Dong Xu

Professor Jia-Dong Xu

School of Electronic and Information

Northwestern Polytechnical University

China

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Progress In Electromagnetics Research M, Vol. 5, 15-23, 2008

doi:10.2528/PIERM08100704 | Google Scholar

Abstract

The critical-points method is adopted for measuring unloaded Q-factor of microwave resonators in the presence of phase shift caused by the feed line. The result is calculated from four frequencies of three points in the resonator's impedance trace. In fact, the resonator's impedance trace rotates in Smith Chart by the phase shift. If Q-factor were gotten directly from the measured impedance including feed line rather than the equivalent impedance of the resonator without feed line, the performance of measurement will be impaired. To de-embed the phase shift, objective function was introduced to find the proper rotation angle caused by the feed line instead of calibration using extra measurement. Another advantage of the proposed method lies in the fact that no special attention is needed to distinguish magnetic coupling and electric coupling. The effectiveness of the proposed method was demonstrated by one set of simulation data and two measurement examples, namely, a low Q dielectric resonator and a high Q hollow cylindrical cavity.

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Changying Wu, Kai Zhang, Gao Wei, and Jia-Dong Xu, "Applying Critical-Points Method in the Presence of Phase Shift Due to Feed Line," Progress In Electromagnetics Research M, Vol. 5, 15-23, 2008.
doi:10.2528/PIERM08100704

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