Multilayered Transmission Lines on Quasi-planar Substrates with Anisotropy

Abstract

Microstrip structures are very widely used in antennas and microwave devices for navigation and communication systems in transport, aeronautics and space. Often there is need to integrate them into the surface of aircraft, satellites and vehicles, which leads to the structures to be conformal. New, lightweight materials (e.g. CFK) are being used more and more exhibiting multilayers with anisotropic behavior. Since the substrate material strongly affects the properties of the structures, the microwave circuit elements need to be modelled very precisely and fast numerical procedures are required to predict their characteristics. This contribution presents the extension of an efficient numerical method, i.e. the discrete mode matching (DMM) to analyze conformal structures with anisotropic materials. This method uses the exact eigen-values of the waveguide modes, which are dependent on the lateral boundary conditions. It requires only 1D discretization along the horizontal tangential direction of the interfaces for the analysis of multilayered transmission line structures as the structure is assumed infinite in the propagation direction and the analytical solution is taken in the direction perpendicular to the interfaces. Here, each layer is defined by a hybrid matrix which relates the tangential field components at its interfaces. The shape of the interfaces can be defined by the suitable equation, from which the slope at each discretization point can be calculated. Consequently the field components are determined for each sampling point in the interfaces with varying slope. Then the dyadic Green’s function (or system equation) is derived using a full-wave equivalent circuit (FWEC) in the space domain. The application is demonstrated by computing propagation constants for quasi-planar waveguide and stripline having uniaxial or biaxial anisotropic dielectric layers.