Study On Analysis And Compensation Method Of Planar Transmission Line Discontinuities

Planar transmission lines (e.g. microstrip line, coplanar waveguide, slotline, etc.) are widely employed in Microwave Integrated Circuits (MICs) and in Monolithic Microwave Integrated Circuits (MMICs). With the development of microwave system integration and miniaturization, people will focus their attention on discontinuities which are aroused by structural changes of transmission line and transition between different kinds of transmission lines. In order to realize high-performance microwave circuits, it is necessary to establish accurate models and to analyze for these discontinuities.Finite-Difference Time-Domain (FDTD) method is applied to investigate microstrip discontinuities systematically in this thesis. As an efficient numerical method in electromagnetic field, FDTD method has become popular and mature in recent years. With the characteristic of simplicity, generality, and flexibility,FDTD has many advantages in dealing with electromagnetic problems. Fundamental principles of FDTD method, basic theory of transmission line and microwave network are first introduced. Different characteristic parameters of planar transmission line discontinuities are extracted by FDTD arithmetic, such as scattering parameters of dominant mode and dispersion parameters. In this thesis, microstrip discontinuities are modeled and simulated by three-dimensional FDTD method. The information of electromagnetic field at any time and any position in the computational region can be obtained by FDTD iterations. Such time domain signals are then processed to get frequency domain parameters. Then, the emphasis of this study was to optimize the electrical performance using simple compensation techniques. On-wafer measurement is a chip test method with high precision. So the transition from the microstrip line to coplanar waveguide is investigated.T-junction and cross junction are two kinds of severe microstrip discontinuities, but they often occur in microwave and millimeter-wave circuits. Their electromagnetic characteristic can be analyzed in accurate way by FDTD method. Their adverse influence can be effectively reduced through some compensation measures. The transition mentioned in this thesis not only have the advantages of wide bandwidth,low insertion loss and low return loss, but also can achieve compact structure.