A Low-Profile Flexible Dual-Band Antenna With Quasi-Isotropic Radiation Patterns for MIMO System on UAVs

In this letter, a low-profile flexible dual-band quasi-isotropic antenna based on half-wavelength crossed dipoles is developed for unmanned aerial vehicle (UAV) applications. Specifically, to decrease the antenna profile, a coaxial structure is used to feed the antenna and no external balun is applied. Theoretical and numerical analyses of the designed antenna were conducted. To validate the design concept, an antenna prototype was fabricated and characterized. Good agreements have been observed between simulations and measurements. The measured radiation patterns show that the gain deviations across the whole spherical radiation surface are less than 7.5 dBi at 2.4 GHz and less than 8.7 dBi at 4.6 GHz. For the purpose of system demonstration, a 2 × 2 multiple-input–multiple-output (MIMO) system employing the proposed antenna was assembled. The resulting dual-band MIMO system was deployed on a UAV for ground test, validating its potential for performance improvement of UAV communications.