  A combination of gap waveguide technology and the traditional coplanar
waveguide is studied in detail and demonstrated experimentally for the first
time. This novel metamaterial transmission line is presented in three different
configurations and offers a broadband operation, low loss, and low dispersion
characteristics. Analytical expressions for its characteristic impedance and
effective permittivity are provided and validated by Finite Element Method
simulations. The loss and dispersion of the line are analyzed with an Eigenmode
solver. The proposed line prevents the propagation of substrate modes in the
band of operation at the same time it reduces the dielectric loss in the line
due to a higher concentration of the E-field over the air. Moreover, its
coplanar layout facilitates the integration of active components. As such, it
is considered to constitute a potential key element in the development of more
efficient, millimeter wave systems.
