Influence of strength and asymmetry of the coupling between a cavity and a transmission line on measurement of complex permittivity

Influence of the strength and the asymmetry of input-output ports on the measurement of complex permittivity by the resonant cavity perturbation method was investigated experimentally.We adopted the |S21| as the criterion of the strength, and the difference between S11 and S22 as the criterion of the asymmetry. When the coupling is symmetric, the real part of permittivity can be evaluated in strong coupling state up to −3 dB of coupling. The imaginary part of permittivity can be evaluated up to −14 dB of coupling. Imaginary part of the relative permittivity e″r was calculated using the conventional equation, which is based on the complete symmetry of the coupling of input-output ports. For the measurement of high-Q materials, calculated e″r is strongly affected by the asymmetry in the strongly coupled region. For the measurement of lossy materials, the inevitable asymmetry and the strong coupling allow enough exact evaluation of e″r. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 706–709, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24988