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The desire to improve high-speed digital signal propagation is the driving force behind research in the area of dielectric characterization. While techniques have been reported for characterizing generic dielectrics, only a few can be applied to printed circuit board substrates. This paper presents a new technique for measuring the dielectric properties of such substrates based on the measured scattering (S) parameters of a transmission line. A discussion of techniques for characterizing the dielectric properties of printed circuit boards is also presented. I n t r o d u c t i o nThe quality of high-speed digital signals is subject to the limitations of the signal transmission network into which components are inserted. As clock speeds continue to increase, circuit designers must be more aware of transmission impairments caused by impedance mismatch, manufacturing tolerances, and transmission line discontinuities. To improve transmission media characterization, techniques to measure the complex permittivity of printed circuit board (PCB) laminates are being investigated. Improved material characterization leads to morc accurate circuit simulation during the design phase and tighter control of signal performance after board fabrication.The most common laminates are fiberglass reinforced resin. Because the composite dielectric is both anisotropic and nonhomogeneous, the electromagnetic field orientation of fabricated planar transmission lines must be preserved in any dielectric characterization test structure.The preservation of field orientation is even more critical considering that multi-layer high-speed composites of such exotic materials as cyanate ester, teflon, and the traditional fiberglass reinforced resin are being proposed. These multilayer structures provide a trade off of the low dielectric constant but high cost of the exotic materials, and the mechanical rigidity, low water absorption and low cost of the fiberglass materials.An additional practical consideration is that existing PCB fabrication processes yield a test coupon (typically 1 cm by 10 cm) for mechanical testing. This coupon could be utilized for substrate characterization of novel composites or for quality assurance of a standard process.Current substrate characterization techniques generally measure both the real and imaginary part of the complex permittivity. Those suited to laminates can be divided into four major categories; resonance, reflection/transmission, time domain reflectometry (TDR), and phase/length comparison. The new method, based on the measured S-parameters of a transmission line, would be categorized under reflection/transmission methods.Resonant method calculations of the complex permittivity are based upon the measurement of the resonant frequency and the quality factor for a resonant circuit of some particular geometry. These methods provide information at only a few discrete, harmonically related frequencies specific to the structures involved [1]- [5].Of the various resonant structures reported only the strip resona...