Antennas and components for modern telecommunication systems including wireless body area networks

With the advancements in wireless communications, there is a constant need to develop novel antennas and components to support modern communication systems. These systems are targeted for applications in medical, defence, healthcare, public security, communications. The antenna is a vital front end component in any wireless system. Although many narrow- and wide-band antennas have been designed over the past decades, still there are several challenges when designing such antennas for modern systems. These challenges include compactness, space constraints, desired radiation characteristics, low cost, light weight, multi-band operation, interference mitigation, reconfigurability, and stable performance under varying conditions. Motivated by the increasing demand for modern telecommunication systems inclusing wireless body area networks (WBAN), this thesis addresses such challenges and presents several solutions. In this thesis, in addition to characterization of carbon nanotube yarns, several antennas are deigned and investigated. The designed antennas are broadly classified into narrow-band antennas, wide-band antennas, embroidered antennas on polymer composites, wide-band antennas with notching, antennas with Frequency Selective Surface (FSS) and High Impedance Surface (HIS) reflectors, and reconfigurable antennas. The narrow-band antennas provide single- and dual-band operation for the2.45GHz industrial, scientific and medical (ISM) band and for 4.9GHz public safety wireless local area network (WLAN)/5GHz IEEE 802.11 WLAN. These antennas have significant advantages of compactness (only 14mm wide), full groundplane to minimize radiation towards the body, a wide radiation pattern over thebody surface to provide maximum coverage, and less sensitivity to the variation of the gap between the antenna and the human body. These advantages make them suitable for on-body communications and wearable applications. The wide-band antennas target ultra-wideband (UWB) systems. One such antenna is fabricated using conductive fibres on polymer composite substrate (PDMS) that is exible and semi-transparent. A UWB antenna with a notch band provides design exibility to reject a desired frequency band. A mathematical expression is presented to predict initial design parameters of these antennas and to avoid excessive numerical computations required otherwise. These antennas are compact, have stable wide radiation patterns and provide band rejection with a high VSWR. FSSs are employed with UWB antennas to achieve a uni-directional pattern by reecting the radiation from the lower hemisphere to the upper hemisphere.The presented design has a stable radiation pattern over a wide bandwidth and is suitable for applications using uni-directional beam. It also helps to save and use the power that otherwise could propagate into the human body, thus are suitable for off-body communications. Periodic and quasi-periodic sequences of modulated line based HIS are also investigated and is used to achieve controlled radiation patterns. Reconfigurable antennas are designed for the 2.45GHz ISM band and 5GHz WLAN to operate in close proximity of the human body. They have same advantages as narrow-band antennas mentioned above. A reconfigurable antenna to provide UWB operation in one mode and a narrow-band operation in another mode is presented. It is designed using a low cost substrate, has planer configuration, avoids the need of vias and has a fully printed bias circuit. Theoretical and experimental characterization of Carbon Nanotubes (CNT) yarns is a valuable contribution that opens new paths of research related to CNT. Electrical properties of CNT yarns were known for Direct Current (DC), however they were not available at RF and microwave frequencies. In this thesis, CNT yarns are modelled as transmission lines and are characterized for a frequency range from 500MHz to 20GHz. Results show that the yarns exhibit a frequency independent resistive behaviour and are suitable for wide-band applications including wireless body area networks.