Tunable Antennas and Microwave Circuits for Next Generation Reconfigurable Front Ends

Reconfigurable antennas and microwave circuits have attracted much attention in recent years due to their advantages compared to conventional designs. It is recognized that systems exploiting a certain extent of tunability potentially benefit from multi-functionality and performance enhancement, which ultimately translates into lower component count, size and overall cost of the transceiver. In this work, a collection of tunable/reconfigurable designs comprising of antennas and passive microwave circuits that spans to different application areas is presented in a comprehensive manner. In chapter 2 a dual frequency reconfigurable antenna array using PIN diodes and its associated phase shifter are presented. The system is capable of operation at two independent frequencies (4.7GHz and 7.5GHz) while switching between four different radiation patterns types for each frequency. Chapter 3 explores the feasibility of a novel of iso-frequency repeater system based on reconfigurable parasitic elements to maximize the isolation between the transmitting and receiving antennas.;In chapter 4, an analytical tuning algorithm for a reconfigurable impedance matching pi-network based on tunable capacitors is presented. The algorithm is able to determine all tunable network component values for matching any given load impedance.;A single pole single zero notch filter using RF MEMS tunable capacitors and its associated frequency control loop system for automatic frequency tracking are presented in chapter 5. The high Q value of the tunable capacitors enables this filter to achieve 22dB rejection with less than 0.8dB insertion loss over a 5MHz bandwidth in the International Mobile Telecommunications band (IMT, 2.1 GHz).;In chapter 6, a set of approximate closed form expressions for the input impedance, resonant frequency, radiation efficiency, quality factor and impedance bandwidth of capacitively-tunable loaded planar inverted-F antennas (PIFAs) used for cell phone applications are presented. Finally, chapter 7 presents a tunable antenna pair for wireless transceivers using RF MEMS tunable capacitors. This design utilizes antenna frequency agility to cover a frequency tuning range from 1850MHz to 2170MHz (16%) corresponding to the cellular wireless bands IMT-I and PCS and is designed to provide built-in filtering between antennas.