Article

# 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: 2.23). 08/2006; DOI: 10.1109/TMTT.2006.877061 Source: IEEE Xplore

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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.IEEE Transactions on Microwave Theory and Techniques 04/2011; · 2.23 Impact Factor - [Show abstract] [Hide abstract]

**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.IEEE Transactions on Microwave Theory and Techniques 12/2011; · 2.23 Impact Factor - Progress In Electromagnetics Research 01/2010; 102:267-286. · 5.30 Impact Factor

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