We propose here a composite right/left handed transmission line constructed by using conductor-backed coplanar strips. In this line, we can easily realize a shunt inductor without via because it has the electric-wall symmetry at the guide center. The left-handed nature is verified by both the finite difference time-domain (FDTD) and the equivalent-circuit calculations. Furthermore, we demonstrate the proposed line can easily satisfy the balanced condition for no band gap between the right-handed and the left-handed modes, and can be applied to a leaky-wave antenna, numerically and experimentally.

Printed transmission lines have been extensively examined so far, but results obtained there are all concerned with the waveguiding conductors with no loss and zero thickness, except very few results. We have recently studied the transmission characteristics of printed transmission lines in detail, when the waveguiding conductors have finite conductivity and thickness, and we have found an unexpected effect that we call a "mode extinction effect. " This effect results in significant changes in the dispersion behavior of the printed-transmission-line fundamental mode. For a critical thickness, it may turn out that such transmission line can not use in open structural configuration, but must always be used by putting into a packaging box. In this paper, we discuss thoroughly this important effect and related results from the standpoints of both the dispersion behavior and the vector field plots. We also show the measured results of the attenuation constant.

We first reported the simultaneous-propagation effect that the leaky dominant mode can be present on conductor-backed coplanar strips at the same time as the conventional bound dominant mode. We have investigated here numerically and experimentally this effect in detail. Consequently, we have found that it occurs under a certain condition of structural parameters, and also have verified that it affects circuit performance significantly.