Impedance Matching Networks for Wireless Applications

Abstract

Impedance matching implies maximum power transfer from source to load as well as minimum signal reflection from the load, in an RF system. This explains the importance of impedance matching networks and their continuously increasing use in many electronic applications, as for example RF power amplifi ers, source-pull and load-pull power transistor characterization or impedance matching devices such as Antenna Tuning Units. The focus of this thesis is on the design, fabrication and test of impedance matching networks. Many diff erent types of practical Impedance Matching Networks are available which is why detailed investigation and analysis are to be done in order to fi nd the most suitable topology for the network. RF MicroElectroMechanical Systems (MEMS) switches are used to design a switched-capacitor bank for the proposed impedance matching network. Several RF switches are analyzed and simulated so that their behavior is known when applied to the capacitor bank. Multiple capacitor banks were designed and fabricated for the purpose of this thesis. The MEMS-based approach provides better performance and wider capacitance ranges as compared to the conventional varactors. It allows the design of impedance matching circuits with di fferent bandwidths and specifi cations, that can be used as part of a dynamically reconfi gurable automatic match control circuit for a wide variety of wireless devices and intelligent RF front ends. For comparison purposes, an impedance matching network using commercial varactors is also simulated and its Smith Chart coverage is presented. The designed circuits are fabricated and measured. The results indicate satisfactory performance and good agreement with circuit simulations.