International Symposium on Antennas and Propagation
Wideband Propagation Constant Characterization for Printed Circuit Board Interconnects
Kuen-Fwu Fuh, Tsung-Wen Chen,
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The issues of signal distortion and electromagnetic interference (EMI) deteriorate as the rise time of signals in printed circuit board (PCB) decreases. Therefore signal integrity (SI) becomes an important topic in modern wideband and high-speed applications for PCB manufacturers and designers [1-2]. The dispersion propagation and frequency-dependent attenuation of PCB interconnects or transmission lines contribute significantly to the SI issues; the propagation characteristics of interconnects or transmission lines in PCB are required by designers to estimate the qualities of communication signals, e.g., eye-diagram evaluation . In addition to precise impedance control, PCB manufacturers now should establish the capability to characterize wideband propagation properties of interconnects and provide useful data for their customers . Propagation constant γ=α+jβ is an eigenvalue of the transmission matrix of uniform transmission line; it can also be viewed as the transfer function of the uniform transmission line. Therefore it contains all the signal transfer characteristics of an interconnect. It is well known that TRL calibration method can extract propagation constant from the measurement of S-parameters of two lines with different lengths [5-6]. Various authors apply this methodology to characterize instrinsic parameters of transmission lines and permittivities of materials [7-10]. Based on the same algorithm and proper numerical process, we have shown that this method can characterize propagation constant of PCB interconnect till 40 GHz. This methodology can help manufacturers and designers to evaluate propagation properties of TEM or quasi-TEM transmission line in real application scenario. In section 2 the mathematical model is derived; the model is examined in section 3 by the aids of commercial circuit and field solvers. Then the propagation characteristics of microstrip lines fabricated on thin PCB substrates are measured. The measured data shows that this methodology can help manufacturers and designers to clarify the issues of dispersive and anisotropic propagations.