Design methodology for multilayer microwave filters and Balun circuits

A systematic and efficient approach to the design for a broad class of passive microwave circuits in multilayer configurations is presented. Multilayer configurations are becoming popular at microwave frequencies due to their several advantages over single layer configurations. However, systematic design procedures for multilayer circuits have not been yet available. Design procedures for several types of microwave circuits in multilayer configurations have been developed. Parallel coupled-line band-pass filters, end-coupled bandpass filters and three-line baluns have been designed with the systematic design procedures developed. Procedures developed have been verified by comparing the results with full-wave electromagnetic simulations. These circuits have also been fabricated and measured to verify the design procedures. Wide bandwidth, size/volume compaction, flexible design and physically realizable dimensions are the factors that multilayer structures provide compared to single layer configurations.; A network modeling is employed to characterize multilayer multi-conductor transmission line systems. Since the microwave circuits developed utilize multiple coupled lines in multilayer configurations, the characterization of these coupled lines plays a significant role in derivation of design equations and generation of design procedures. Using this modeling approach, a multiple coupled line system can be transformed to a multiple uncoupled line system. These equivalent uncoupled lines are used to derive network parameters ([S], [Y] or [Z] matrix) for coupled lines. The normal mode parameters (NMPs) for coupled lines derived in terms of system specifications are utilized to obtain the physical geometries. An optimization process is employed to find the geometries which yield the desired NMPs calculated from circuit specifications. For optimizing the geometry, a quasi-static field analysis program, Segmentation and Boundary Element Method (SBEM), is employed to calculate inductance and capacitance matrices for specific dimensions of the multilayer configurations. A general optimization algorithm, Simplex method, is used in conjunction with SBEM to obtain the physical geometry for various coupled lines. Sometimes, this optimization process generates local minima and takes considerable time in computer simulation. Therefore, an Artificial Neural Network Modeling (ANN) is used to save the optimization time. Because end-coupled band-pass filters employ gap coupled sections, the 2-dimensional SBEM is not applicable for optimizing the gap dimensions. In this case, an ANN model has been developed and used to design this kind of filters based on the procedure developed here.; Two case studies of parallel coupled-line band-pass filters are presented following the design procedure developed. A quasi-static analysis by SBEM and simulation result from a full-wave electromagnetic simulator are presented along with measurements for verification. Two designs of parallel coupled filter carried out in coplanar waveguide (CPW) are also reported. Three-line baluns have been designed in two layer structures, simulated and verified by measurement results. Two examples of multilayer end-coupled band-pass filters have been designed using the procedure developed. One example of these filters is also designed with an ANN model for comparison. A discussion of results from these circuits and suggestions for future work are presented.