Leaky waves on broadside-coupled microstrip

Broadside-coupled microstrips with and without conducting side walls are studied using a full-wave spectral-domain analysis. Special attention is directed towards possible leakage to the parallel plate mode and its potential effects in practical integrated circuits. It is asserted that for appropriate geometrical parameters, broadside-coupled microstrips can be leaky at all frequencies. Instructive comparisons between the modes on broadside-coupled microstrips with and without side walls are made by means of dispersion curves and field plots. From the comparison, approaches for reducing the low-frequency leakage are proposed.>