Computer-aided design of passive microwave circuits using optimization algorithms

Passive microwave components have wide-found applications in many areas ranging from cellular phones, satellite navigation, Wi-Fi to the humble car locking key-fob. With the entering of fifth generation era of mobile networks and a new era of the Internet of Things, the range of radio frequency electronics applications is set to increase, thereby introducing newer problems to solve. Performing experimental studies to optimize a microwave circuit involves design of same circuit with different length, width and spacing, often times increasing the cost. CAD based simulations can simulate a microwave circuitry for wide range of design parameters at no extra cost, thereby allowing us to optimize its components. In the present work, three passive microwave circuits have been considered for optimizing their performances subject to design constraints. The circuits considered are; (i) impedance matching transformer, (ii) band-stop filter and (iii) band-pass filter circuit. These three circuit components were designed using a coarse model based Advanced Design System (ADS) tool. A suite of optimization algorithms present in ADS tool were tested for quick convergence to optimal design value subject to design constraint(s). The goal of optimization is set in terms of Scattering parameter (S-parameter) whose value depends on impedance applied at input and output ports. The design parameters are length, width and/or spacing of micro-strip lines. Analytical expressions are also derived to find characteristic impedance (Z0) of the circuit using static approach to micro-strip analysis. Entire circuit is divided into multiple segments; each segment is solved individually such that the result of next segment is applied to the preceding segment until the boundary impedance of the circuit is obtained. The impedance value thus obtained is analytically converted into S parameter by multi-port network analysis and compared against ADS simulations. The design parameters that satisfy constraints in the form of S-parameter is set to form optimum solution space from which optimal values are obtained.Master of Science (Communications Engineering