Wideband measurement of the dielectric constant of an FR4 substrate using a parallel-coupled microstrip resonator

YDI Wireless, Baltimore, MD, USA
IEEE Transactions on Microwave Theory and Techniques (Impact Factor: 2.24). 08/2006; 54(7):3127 - 3130. DOI: 10.1109/TMTT.2006.877061
Source: IEEE Xplore


We have made a wideband measurement of the real part of the dielectric constant of flame retardant #4 epoxy (FR4), a common high-frequency printed-circuit-board insulator. We designed a novel test circuit, an electrically long parallel-coupled microstrip resonator, which was etched on a 0.014-in FR4 substrate, manufactured by NELCO, Melville, NY. We used a computer model of the resonator to extract the dielectric constant at the frequencies of zeroes in its measured transmission response. By adjusting the model's dielectric constant, we tuned the frequency of each zero to match the measured frequency, yielding the dielectric constant at that frequency. To validate our method and results, we present a simple, but original proof that the frequencies of zeroes in the resonator's transmission response are insensitive to input and output mismatches. Additionally, we compare the measured and predicted response of a two-stub filter designed with our measured data. The fabricated filter's measured return loss and insertion loss from 3 to 12 GHz are within 1% of the predictions of Agilent Technology's Momentum.

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    • "Many planar-circuit resonant methods have been developed for the complex permittivity measurement of substrate materials. These methods can be implemented in various types of planar transmission line technologies, including microstrip [5], [6], stripline [7], [8], and coplanar waveguide (CPW) [9]. "
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    ABSTRACT: A differential measurement technique for extracting the complex permittivity of substrate material and the effective conductivity of rough conductor surface is proposed in this paper. In this method, substrate integrated waveguide (SIW) cavity resonators having the same footprints and varied thicknesses are utilized to separate the conductor loss of the top and bottom surfaces of SIW cavity resonators. The extraction of effective conductivity from the surfaces of SIW cavities is done through examining the difference of unloaded Q-factors between the SIW cavity resonators with varied thicknesses. In advance of getting knowledge of the dielectric loss of substrate material, the conductor loss contributed by the metallic via array must be characterized. The separation between the conductor loss of metallic via array and dielectric loss of substrate material is done through the analysis and comparison of unloaded Q-factors between the SIW cavity resonators with the same length but different widths. In order to verify the proposed method, complex permittivity of a commercial substrate is measured with this method at microwave frequencies. The extracted dielectric properties of substrate material are generally consistent with that provided by the manufacturer.
    Full-text · Article · Feb 2015 · IEEE Transactions on Microwave Theory and Techniques
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    • "To validate design formulas and modified equivalent circuits of a transmission-line section, a microstrip Marchand balun terminated in and was fabricated on a substrate (FR4, , mm). The dielectric constant of FR4 is found based on a third-order polynomial [34]. dB and a design center frequency of 1.5 GHz were chosen. "
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    ABSTRACT: New design formulas for impedance-transforming 3-dB Marchand baluns are proposed. They are about the even- and odd-mode impedances of the coupled transmission-line sections of the Marchand baluns and determined by coupling coefficients together with termination impedances. The particular property proposed in this paper is to choose the coupling coefficient arbitrarily, resulting in infinite sets of design formulas available. This is quite different from the conventional design approach in which only one coupling coefficient is possible. For the perfect isolation of the Marchand balun, an isolation circuit (IC) is needed, being composed of two 90° transmission-line sections and resistance(s). Sufficient area to build such a long IC is, however, inherently not available. For this, ways to reduce the IC size are also suggested. To validate them, a microstrip Marchand balun terminated in 130 and 70 Ω is designed at a design center frequency of 1.5 GHz and tested. The measured results are in good agreement with prediction, showing that power divisions are 3.57 and 3.262 dB, return losses at all ports are better than 21 dB, and the isolation is better than 20 dB around the design center frequency. The measured phase difference between two balanced signals is 180°±2° in about 50% bandwidth.
    Preview · Article · Dec 2011 · IEEE Transactions on Microwave Theory and Techniques
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    • "In particular, the effects of EM analysis accuracy, metal surface roughness, metal thickness, and the cross-sectional profile of the metal edge (due to etching) have been found to be important and are discussed in detail. A detailed bibliography of planar substrate dielectric measurement techniques is provided in [8]. "
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    ABSTRACT: An improved technique to measure uniaxial anisotropy in planar substrates is described. This technique builds on previous work performed with stripline. The improved approach offers substantially larger bandwidth, lower error, and ease of measurement. An almost complete automation of the entire calibration and measurement extraction process is described. It is also demonstrated that the horizontal (parallel to substrate surface) dielectric constant is less than the vertical dielectric constant for glass fiber weave reinforced substrates for the purposes of microstrip and stripline design. This directly conflicts with bulk measurements of dielectric constant and is believed due to microstrip horizontal electric field concentrating in the substrate surface. This is supported by measurements of a homogeneously ceramic loaded substrate showing the expected relationship. Effects of electromagnetic analysis accuracy, metal roughness, metal thickness, and edge profile (due to etching) are found to be important.
    Preview · Article · Apr 2011 · IEEE Transactions on Microwave Theory and Techniques
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