Realization of innovative wearable antennas using conductive textile-polymer composite

This thesis presents the realization of innovative wearable antennas using conductive textile-polymer composite. Initially, comprehensive research on recent developments in fabrication methods for flexible antennas and investigation into the requirements for innovative antennas for wearable modern communication systems were conducted. After recognizing these requirements, several novel flexible antennas were developed in this thesis. These antennas include conformal low-profile ultrawideband (UWB) antennas with and without a band-notch and a reconfigurable pattern antenna. After reaching a good agreement between simulated and measured results, this thesis shows that these novel antennas with a simple design and low-profile structure can be realized in wearable formats and can be employed in a wide range of applications. UWB antennas with monopole-like radiation characteristics have recently attracted attention due to the extensive demands in broadband wireless communication, as they provide high data rate transmission over a short distance, low power consumption, and robustness against multipath. These antennas have a wide range of applications in unmanned aerial vehicles (UAVs), wireless body area networks (WBANs), self-managing ground sensor networks, and in-vehicle sensing. In addition, antennas with pattern reconfigurability capabilities between monopole-like and broadside patterns enhance the performance of wireless communication systems by avoiding interference with noise sources. These antennas also provide wider coverage, save energy, and offer extra functionality in a space-saving structure. The applications of these antennas include cognitive radio, indoor wireless network, base station, WBAN, and multi-input multi-output (MIMO) systems. In recent years, wearable and conformal antennas have been attracting increased attention in all the aforementioned applications because modern communication systems are moving more toward flexible and wearable structures. The flexible forms of antennas allow the system's deployment with different platforms and optimize the limited spaces in systems. Despite the many studies and works presented in this area, the antennas mentioned above, which have extensive applications, have not been realized in a wearable form. In addition, in most of the presented works, the structures are either high in profile or complex in design or in feeding networks. Therefore, there is a demand for the design of these novel antennas with low-profile and simple structures and their realization with existing wearable fabrication methods. Initially, comprehensive research and the process of navigating through recent developments to fabricate wearable antennas and wearable reconfigurable antennas were conducted. Then, among various approaches, polydimethylsiloxane (PDMS)-embedded conductive fabric was chosen to be used in this research due to its many strengths and fewer limitations in the fabrication of planar antennas over other presented methods. This simple method provides robust and flexible antennas through an encapsulation structure. Moreover, by researching wearable reconfigurable antennas, limited efforts were found to develop wearable dynamic pattern reconfigurable antennas. Therefore, the following innovative antennas are realized in this thesis. In the first proposed novel antenna, the idea of designing a planar antenna with the electronically tuning capability of its radiation pattern at 5.8 GHz ISM band was investigated. The proposed antenna was realized by using rigid materials to save on the cost and time of the design and fabrication of a wearable format. Active circuit elements, including diodes, resistors, capacitors, inductors, a switch, and a battery, are integrated with this simple and low-profile antenna. The second novel wearable antenna was a reconfigurable antenna at 5.2 GHz. This antenna was developed after performing comprehensive research on wearable reconfigurable antennas and the idea of changing the current distribution for pattern reconfigurability. In contrast with the other presented works in this area, this circular patch antenna is planar in structure, and its pattern can be switched electronically between broadside and monopole-like patterns without any use of rigid shorting posts or a complex feeding network. All the antenna parts, including the diodes, RF switches, wires, and DC biasing circuit, are fully encapsulated by PDMS in this novel antenna. To evaluate the effects of the active components on the antenna, its performance was investigated under various bending conditions. The third novel design developed was a simple planar conformal UWB antenna with monopole-like radiation patterns and a 10-dB return loss bandwidth from 2.85 to 8.6 GHz. This structure was the first conformal UWB antenna with monopole-like radiation patterns reported in the open literature. This design was fabricated, and the structure was experimentally tested under both flat and bent conditions. The system-fidelity factors (SFFs)1 of the antenna were investigated to evaluate its suitability for UWB communication. To further evaluate the practicability of the fabrication method on the UWB structure and the effects of unconventional materials on the antenna performance, the measured mean realized gain (MRG)2 of the antenna from 2.85 to 8.6 GHz was calculated to validate the maintaining of monopole-like radiation patterns throughout the frequency band. This parameter provides a more complete view of the antenna performance over the entire bandwidth. It verifies that the full instantaneous bandwidth can be utilized for communications in this antenna. The fourth novel structure was an UWB antenna with a bandwidth from 3.8 to 8.3 GHz, and a notch at 5 to 6 GHz. This low-profile antenna with only a 0.046 λ0 height at 3.8 GHz is highly flexible. Its flexibility, together with its low profile, makes this antenna a suitable candidate for wide coverage in all directions where the antenna is placed on non-flat surfaces. The proposed conformal antennas in this thesis are widely used in a variety of applications and are excellent for environments with a variety of environmental factors such as heat and moisture. This increases the system’s durability, reliability and sustainability.