Properties of CPW in the Sub-mm Wave Range and Its Potential to Radiate

In recent years, new technologies of monolithic integrated circuits have been pushing utilization of the CPW as far as the sub-mm wave range [1-3]. Additional new findings on CPW characteristics and behaviour have in this way been revealed step by step. Our paper contributes to this process. Detailed investigation of possible higher order leaky waves that may occur on the CPW has allowed us to make a new interpretation of the measured dispersion characteristics [2] of the CPW, made on a high resistivity Si substrate, in the frequency range up to 700 GHz. For a microwave designer, it is very important to know the frequency up to which the line transmits only the bound wave. This upper cutoff frequency has been determined, and data are available for a wide range of line cross-sectional dimensions and substrate permittivities. CPW also has the potential to radiate space leaky waves. We report theoretical identification of the space leaky waves on the CPW. Tzuang and Lin discovered, and later experimentally verified, this type of leaky wave two years ago on the suspended microstrip line [4,5].