Optimization of microstrip-to-via transition for highspeed differential signaling on printed circuit boards by suppression of the parasitic modes in shared antipads

This paper discusses the behavior of the microstrip-to-via transition for high-speed differential signaling considering the frequency range up to 100 GHz. In particular, the generation and propagation of higher order parasitic modes at the shared antipad area are studied and their impact on differential signal quality is analyzed. A combined antipad scheme that uses separate instead of shared antipads on the outer reference planes is proposed for the suppression of the parasitic modes and at the same time maintaining impedance uniformity along the via segment. Full-wave simulation results show a considerable improvement of signal transmission by the proposed scheme, especially in the frequency range from 40 to 60 GHz for the microstrip-to-via transition in multilayer printed circuit boards.