Flexible materials for ultra wideband antenna design

Abstract

The demand for ultra-wideband (UWB) antennas increases rapidly with the magnified growth of the wireless systems aiming to support wireless and mobile services by simplifying the systems and to reduce the overall device dimensions, and costs. Vast efforts are offered to the development of UWB antennas that aim to improve the seamless integration with various handheld devices such as laptops, mobile phones, and vehicles such as airplanes, cars, and ships. Consequently, the mechanically flexible antennas are the most suitable for such requirements rather than the antennas based on rigid substrate technology. Hence, the antenna should be conformal and able to be conveniently conformed onto the device’s body surface or to be fabricated using the same material in which the devices are fabricated. Subsequently, in some scenarios, the flexible antenna should be optically transparent to overcome the visual impact of the massive use of the antenna in indoor and public areas. Low-cost antenna fabrication technologies are highly expected to take place in future UWB antenna requirements for more economical resource utilization. Generally, UWB systems require the antenna with high efficiency, however, maintaining a high efficiency while achieving extremely wide bandwidth in UWB system is a challenging task. Therefore, conduction and dielectric losses should be minimized in UWB antenna by using highly conductive and low dielectric loss materials. Metals are commonly used as antenna radiating elements because of their high conductivity. However, the poor mechanical flexibility of the metals limit their usage for flexible and conformal applications. The question arises if non-metallic flexible conductive materials having conductivity close to metals can be integrated into the flexible dielectric materials to replace metals. This thesis proposes fabrication techniques to integrate flexible conductive materials into flexible dielectric materials to fabricate transparent UWB antenna and Polymer Matrix Composite (PMC) antenna with improved performance for conformal applications. Moreover, the research evaluates a new low-cost instant printing technique to print UWB flexible antenna with good performance. A technique is proposed to integrate a transparent conductive fabric tissue into a transparent PDMS to fabricate a flexible and transparent UWB antenna with improved performance. The fabricated antenna exhibited an efficiency over 75% and a maximum gain of 4.5 dBi. Moreover, an integration process is proposed to fabricate a flexible PMC composite UWB antenna by integrating the conductive fabric tissue into Eglass fiber mate using Vacuum Infusion Process (VIP). The technology is assessed by fabricating UWB antenna for conformal applications and the results showed high efficiency over 80% for the UWB antenna. Furthermore, a UWB antenna is printed instantly onto a Polyethylene Terephthalate (PET) substrate based on chemical sintering silver inkjet technology using ordinary inkjet printer and the measured results present over 80% of efficiency for antenna. ABSTRACT