Portable Device Antennas Using Reactive Components

Abstract

Rapid progress in wireless communications has led to the decreasing sizes of many portable devices. With the constant demand for terminals that are smaller and lighter, designing a compact antenna has become one of the major problems in wireless communications technology. Chapter 1 of this dissertation considers the relationship between antenna size and bandwidth. Chapters 2 and 3 propose two methods for a multi-wideband or miniaturized antenna using reactive components. Chapter 4 summarizes the important points of the proposed methods. Chapter 2 presents three antennas wherein distributed reactive components are used to control resonant frequencies. In Section 2.1, an inductor or a capacitor is inserted in parallel with an antenna structure, and the resonance shifts are determined by the type of reactive component and its position. To select the positions of the reactive components, voltage distributions of a transmission line model are observed as functions of the resonant modes. The method in Section 2.2 uses the series insertion of a parallel LC resonator that provides variable inductance prior to its resonance. This variable inductance produces different resonance shifts for each resonant frequency, which helps to obtain a wide bandwidth.