Large FoV Direction-Finding System Based on a Small-Aperture Phase Mode Antenna and its Applications on UAVs

Unmanned aerial vehicles (UAVs), serving as small mobile platforms, are well-suited for emitter detection and localization tasks in dynamic environments. However, implementing large antenna array apertures on the compact platform of UAVs is impractical. This article presents a small-aperture phase mode antenna (PMA) direction-finding (DF) system for UAV applications. Initially, a small-aperture, high port-isolation dual-port PMA is introduced. Through miniaturization and decoupling, a conventional slot antenna pair is transformed into the final dual-port PMA. The dual-port PMA features a compact aperture of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.4~\lambda \times 0.47~\lambda $ </tex-math></inline-formula> (where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> is the wavelength at 2 GHz), with port isolation reaching up to 40 dB. Next, we investigate the integration of the dual-port PMA with a novel amplitude-only DF (AODF) method, termed the single PMA multiple patterns amplitude comparison (SPMAMP-AC) method. This method utilizes multiple patterns to construct a DF function cluster, providing higher DF accuracy over a broader Field of View (FoV) compared to the traditional AODF method. The measured results indicate maximum DF errors of 2.4°, 4.3°, 4.9°, and 7.9° for FoVs of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$60{^{\circ }}~(\theta \in $ </tex-math></inline-formula> [−30°, 30°]), <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$140{^{\circ }}~(\theta \in $ </tex-math></inline-formula> [−70°, 70°]), <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$160{^{\circ }}~(\theta \in $ </tex-math></inline-formula> [−80°, 80°]), and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$180{^{\circ }}~(\theta \in $ </tex-math></inline-formula> [−90°, 90°]) in the yoz plane, respectively.