Accurate hybrid-mode approach for computing modes in three-line coupled microstrip structure in overlaid configuration

The behaviour of guided modes in three-line coupled micro-strip configuration with a dielectric overlay is examined by the spectral-domain technique. It is shown that by use of an additional substrate layer of adequate dielectric permittivity the phase velocities of three fundamental modes can be made nearly equal. Then a pattern of a six-port microstrip coupler is shown to illustrate theoretically proved results.