Evaluation of Effective Conductivity of Copper-Clad Dielectric Laminate Substrates in Millimeter-Wave Bands Using Whispering Gallery Mode Resonators

Thi Huong TRAN  Yuanfeng SHE  Jiro HIROKAWA  Kimio SAKURAI  Yoshinori KOGAMI  Makoto ANDO  

IEICE TRANSACTIONS on Electronics   Vol.E92-C    No.12    pp.1504-1511
Publication Date: 2009/12/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E92.C.1504
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electronic Materials
millimeter wave measurement,  Whispering Gallery mode resonator,  complex permittivity,  conductivity,  dielectric substrates,  

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This paper presents a measurement method for determining effective conductivity of copper-clad dielectric laminate substrates in the millimeter-wave region. The conductivity is indirectly evaluated from measured resonant frequencies and unloaded Q values of a number of Whispering Gallery modes excited in a circular disk sample, which consists of a copper-clad dielectric substrate with a large diameter of 20-30 wavelengths. We can, therefore, obtain easily the frequency dependence of the effective conductivity of the sample under test in a wide range of frequency at once. Almost identical conductivity is predicted for two kinds of WG resonators (the copper-clad type and the sandwich type) with different field distribution; it is self-consistent and provides the important foundation for the method if not for the alternative method at this moment. We measure three kinds of copper foils in 55-65 GHz band, where the conductivity of electrodeposited copper foil is smaller than that of rolled copper foil and shiny-both-sides copper foil. The measured conductivity for the electrodeposited copper foil decreases with an increase in the frequency. The transmission losses measured for microstrip lines which are fabricated from these substrates are accurately predicted with the conductivity evaluated by this method.