Planar Microstrip Transmission Line Improvements In The Spectral Domain Calculation Method

Microstrip is one kind of main planar transmission lines in MMIC, have been widely used in microwave circuit design. The existing numerical model of microstrip is complicated, and there are some difference between the computing result and design result. So it is important to develop a rapid and accurate research method.In this research, we compute the effective dielectric constant of microstrip lines using spectral domain method with several types of basis function. Then developed the method's decision with a serious improvement to achieve practical demand of convenience and accurate. The research focus on the key problems in implementation of the method, such as, the selection of basis function and the simplification of numerical calculation, eventually summarize some suggestions by comparative study.We derived a Green Function in spectral domain for arbitrary shape layered microstrip by transfer matrix method and spectral domain immittance method respectively, then adopted Galerkin's MoM based on integral equation in spectral domain, gain phase constant and character parameters of microstrip by solving a derived eigenfunction. Later, an analysis of dimension and configuration effect on characters has been done, and also studied the key problems in the numerical calculation of Galerkin's MoM: the simplification of integral equation of open microstrip, elimination of spurious root, and numerical method of nonlinear equation. We also take a comparative study of the convergence of basis function, and described the reasonable choice of basis function for different dimension. At last, we verified the numerical results by compare with results from commercial software HFSS, the comparison results show the method can achieve same decision with HFSS almost, but less time required, and the comparison with experimentation measurements also demonstrate the result is useful for design in practical.