Low-Profile Triple-Element Antenna for UWB Indoor Localization in Handheld Devices

This paper presents a low-profile, triple-element ultra-wideband (UWB) antenna designed for angle of arrival (AoA) estimation in both azimuth and elevation across UWB channels 8 to 14 (7.2–10.2 GHz). Fabricated on thin polyimide (PI) substrates with a total thickness under 150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m, it is suitable for compact IoT devices, including handhelds for indoor localization. Fully enclosed striplines with radiating slots replace conventional half-open microstrip lines, enhancing impedance bandwidth and radiation performance. Each element includes a coplanar waveguide connected via a buried via. Decoupling ground (DG) structures and neutral lines (NL) reduce mutual coupling and improve bandwidth. A prototype using two flexible PI-based copper laminates was fabricated and measured in an anechoic chamber. Elements 1 and 3 exhibit unidirectional patterns, while element 2 is bidirectional. With its compact size and diverse patterns, the antenna supports efficient indoor UWB positioning.