QUASI-STATIC CHARACTERISTICS OF A 2-CONDUCTOR MULTILAYER MICROSTRIP TRANSMISSION-LINE WITH DIELECTRIC OVERLAY AND A NOTCH BETWEEN THE STRIPS

Different methods for controlling the coupling between a two-conductor microstrip transmission line axe investigated in this paper. The tran smission line consists of two thin perfectly conducting strips with a rectangular notch between the strips, two layers of dielectric substra te, and a dielectric overlay. The formulation and solution technique a re based on the equivalence principle, a free space Green's function, and the method of moments. It has been found that the coupling between the conducting lines can be reduced significantly if dielectric mater ial between the lines is removed. Further reduction in coupling is obs erved when the relative permittivity of the upper substrate layer is m ade smaller than that of the lower substrate. Coupling can be maximize d if the notch is filled with dielectric material having large relativ e permittivity compared to that of the substrates. If the strips axe c overed with a dielectric overlay (or superstrate), the coupling will b e substantially increased. Moreover, with the right combination of die lectric material layers and the right geometry, it is possible to equa lize the even- and odd-mode phase velocities while having some control over the coupling capacitance.