RESONANT PHENOMENA IN CONDUCTOR-BACKED COPLANAR WAVE-GUIDES (CBCPWS)

This paper presents a thorough and systematic investigation of resonan t phenomena in conductor-backed co-planar waveguides (CBCPW's). We use d a full-wave analysis first to establish benchmark results and a seri es of measurements have been conducted to confirm the theoretical resu lts. As many as ten structures of different side-plane patterns were b uilt and tested. All the test circuits exhibit many resonances over a frequency range, as measured in terms of two-port scattering parameter s. Our full-wave analysis is capable of analyzing shielded guided-wave structures with finite-width substrate, and yields the scattering par ameters of the coplanar waveguide circuits accounting for the overmode d-wave propagation. Finally, simple models are developed for physical understanding and interpretation of the resonant phenomena. When treat ing the side planes as patch resonators, we show that the resonant fre quencies can be accurately estimated by this simple model. Followed by another MSL (microstrip-like) model, which considers the excitation o f the first and the second MSL modes, the resonant frequencies thus ob tained are also shown to be in very good agreement with measured resul ts. By displaying the current distributions on the conductor strips in the through or resonant states of the test circuits, the MSL modes of resonances or the patch-type resonances can be clearly seen. When res onance occurs, the electromagnetic energy is confined or carried under neath the side planes and the signal energy can hardly propagate throu gh the central signal line of the test circuit.