Fast Accurate Hybrid Mode Computation of Nonsymmetrical Coupled Microstrip Characteristics

A numerically efficient rigorous spectral domain solution of the wave equation is presented for covered and open nonsymmetrical coupled microstrip lines. Dispersion characteristics of the two fundamental quasi-TEM modes existing on this structure are given and found to agree excellently with measurement. In addition, the associated characteristic impedances of the unequal strips to ground and the line losses are computed from the eletromagnetic field. With this set of design data the four-port admittance matrix of a nonsymmetrical coupled line section is calculated taking the different modal phase velocities into account. As an example of application and as a further test for the computed results elementary microstrip bandfilter structures are analyzed.