Main cause of resonance appeared around 7.5GHz on the frequency response of S-parameters of PWB

Hardware engineers engaging in the mobile system pursue lower power, less weight and higher performance by minimizing the main factors impacting the Printed-Wiring-Board (PWB) performance which involve a large number of discontinuities. It happens to meet the abnormal phenomenon like a resonance, even in the PWB comprised of only the transmission lines connected one after another in series with via-junctions of 10. However it is not encountered in a case connected by a few via-junctions, and the field solver used ordinarily for checking the abnormality would not predict it. The main cause of the resonance appeared around 7.5 GHz on the frequency response of the S-parameters of the PWB with plural transmission lines connected one after another in series by the via-junctions was investigated by the network analyzer and an equivalent circuit model. And the characteristic impedance mismatches among the transmission lines was found out to be the main factor for this phenomenon.