Finite Substrate Microstrip Transmission Line Analysis Using the Characteristic Green's Function-Complex Images Technique

Quasi-static characteristic impedance of a microstrip transmission line on a finite dielectric substrate is calculated by implementing a novel closed-form Green's function in the method of moment (MOM). The Green's function is derived by using the Characteristic Green's Function-complex images (CGF-CI) technique. In this technique, the original 2-D structure is separated into two 1-D layered media surrounding the source. The 1-D Helmholtz's equations are then solved for each of the layered media with proper boundary conditions to find the respective characteristic Green's functions. Combining these 1-D characteristic Green's functions in an integral form gives the spatial Green's function for the original structure. The complex images technique is then applied to this integral form to derive the closed form representation of the spatial Green's function. Since the structure is non-separable, the derived Green's function is an approximate solution especially in the corners. Nevertheless the calculated characteristic impedances show good agreements with other numerical techniques.