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.