Compact multifunctional antennas for wireless systems

Chapter 2

Multifunctional Passive Integrated Antennas and Components

2.1 Development of Passive Integrated Antennas and Components

In the past few decades, many advances have been reported in the development of active integrated antennas (AIAs) (1–5), which were designed by incorporating various active devices, such as an amplifier, mixer, oscillator, duplexer, or rectifier, in an antenna. Being multifunctional, an AIA integrates various signal-processing functions into an antenna to enhance the antenna bandwidth, increase the effective length of a short antenna, reduce the coupling of an array, and improve the noise factor (1, 3). Most important, such integration can help in cutting down the signal transmission path and hence reduce the chance of picking up additional electronic noise. Recently, rapid advancement in millimeter-wave technologies has drawn significant attention to the research and development of passive integrated components (PICs). In modern microwave systems it is very desirable to integrate several functions into a single module to achieve high compactness, low loss, and low cost. Generally, there are two types of multifunctional PICs, one of which combines multiple resonators to obtain multifunctionality, while another achieves multiple functions in a single resonator. In the past two decades, many multifunctional PICs, such as the antenna filter (6–11), balun filter (12–15), phase-shifter filter, antenna package (16, 17), and antenna circulator (18, 19), have ...