CHARACTERIZATION OF ASYMMETRIC COPLANAR WAVE-GUIDE DISCONTINUITIES

A general technique to characterize asymmetric coplanar waveguide (CPW ) discontinuities with air bridges where both the fundamental coplanar and slotline modes may be excited together is presented. First, the C PW discontinuity without air bridges is analyzed using the space-domai n integral equation (SDIE) approach. Second, the parameters (phase, am plitude, and wavelength) of the coplanar and slotline modes are extrac ted from an amplitude modulated-like standing wave existing in the CPW feeding lines. Then a 2n x 2n generalized scattering matrix of the n- port discontinuity without air bridges is derived which includes the o ccurring mode conversion. Finally, this generalized scattering matrix is reduced to an n x n matrix by enforcing suitable conditions at the ports which correspond to the excited slotline mode. For the purpose o f illustration, the method is applied to a shielded asymmetric short-e nd CPW shunt stub, the scattering parameters of which are compared wit h those of a symmetric one. Experiments are performed on both disconti nuities and the results are in good agreement with theoretical data. T he advantages of using air bridges in CPW circuits as opposed to bond wires are also discussed.