Surface wave excitation and coupling mechanisms in PCBs and microstrip circuits

Surface waves, especially the fundamental substrate-guided TM
₀
^z
mode, are excited by any kind of discontinuity in RF printed circuit boards (PCBs) and planar microwave circuits. This special type of substrate-bound radiation is highly increasing with frequency and can become a dominant coupling mechanism in planar circuits. In this paper, an efficient method is presented to calculate correctly the field distribution of the excited surface-waves and a novel theory for describing the coupling mechanism is developed in general for single-port discontinuities with arbitrary vertical and horizontal current distribution.