BEND-INDUCED EVEN AND ODD MODES IN PICOSECOND ELECTRICAL TRANSIENTS PROPAGATED ON A COPLANAR WAVE-GUIDE

A picosecond time separation between the two sides of a single electrical transient propagated on a bent coplanar waveguide has been observed using a subpicosecond electro-optic sampling system. The separation corresponds to the geometrical path difference introduced by a 90-degrees coplanar waveguide bend. Contrary to the straight waveguide where the transient propagates in the odd mode only, the bend forced the signal to emerge as a superposition of both the odd and even waveguide modes. Introduction of proper local grounding in the bend area, by wirebonding the ground lines on both sides of the transmission line, suppressed the unwanted even mode while preserving the standard odd-mode propagation.