Design and Optimization of Tunable Matching Networks and Aperture-Tuned Antennas for Mobile Wireless Devices

Abstract

In the current wireless market, users have a high level of expectations regarding the functionalities and services added to their wireless mobile devices. At the same time, they also expect performance to remain optimal. In order to meet users’ heightened expectations, the level of integration between different subsystems of wireless radios must increase exponentially to keep pace with the increased demand of functionalities. For example, the current size limitations for mobile wireless devices allow space for only a single antenna, but this antenna must cover dual frequency bands, the first extending from 800MHz to 960MHz and the second from 1710MHz to 2300MHz. Extending the antenna bandwidth to cover the lower edge of the spectrum without increasing the physical size of the antenna is a challenging task. Meanwhile, there is also a demand to decrease antenna size to achieve more compact wireless mobile devices and to free up space for newly added features. One means to achieve these contradicting requirements is to use impedance tuners to enable a small-sized antenna to cover wider range of frequencies. In this thesis, we investigate some methods of applying impedance tuners. First, we conduct a comprehensive study on the tuning range of multiple network topologies, after which we present a design method to substitute impractical and expensive variable inductors with practical and relatively inexpensive fixed inductors connected to variable capacitors. These serve as building blocks for impedance tuners. This is followed by a performance investigation of a readily available tunable capacitor. The equivalent circuit is extracted at different bias voltages and across the frequency range of interest. This circuit model is used in the fourth part of this thesis as an input to the simulator. Next, we conduct multiple simulation runs to demonstrate the major differences between two methods of impedance tuning: a tunable matching network and an aperture-based antenna tuning. The simulation results demonstrate the performance limitations of each technique. Finally, we verify the study findings by measurements in an anechoic RF chamber, discovering that the conducted measurements conform to the obtained simulation results.