Calculation of characteristic impedance for parallel coupled stripline based on eigenmode analysis and equivalent network

Exact calculation of characteristic impedance for a single and a parallel coupled stripline or microstrip line is needed to analysis and synthesis of stripline circuits. There are many calculation methods for the stripline with zero thickness or finite thickness of strip conductor. Analytical solution for zero thickness has already been given by conformal mapping method, but that for finite thickness have not been given and approximated solution has been given by fringing capacitance method. Here, we propose a new and systematic mode analysis method, which is based on eigenmode expansion and lateral equivalent network. Exact characteristic impedance for narrow-side coupled parallel stripline with any strip thickness including zero thickness can be obtained by a line integral of electric field and a contour integral of magnetic field.