A Balloon Conformal Heterogeneous Array Antenna with Ultrawide Bandwidth and Half-Space Beam Coverage

This article presents a balloon-based conformal heterogeneous array antenna with ultrawide bandwidth and half-space beam coverage for emergency communication applications. The antenna consists of two types of cylindrically conformal arrays, each of which contains nine broadside or endfire subarrays. By virtue of 1-D full-azimuthal beam switching and combining the radiation patterns of those two arrays, one yields an entire half-space beam coverage. To increase the bandwidth and gain while maintaining low profiles, the broadside subarray utilizes $1\times 4$ dumbbell-shaped full-wavelength dipoles cross-fed in series and backed by a miniaturized artificial magnetic conductor (AMC); the endfire subarray employs $2\times 3$ size-tapered half-wavelength dipoles with optimized spacing to achieve the desired radiation characteristics. To validate the designs, the prototypes of two conformal subarrays with one shared aperture were fabricated and measured. Experimental results have indicated the proposed conformal heterogeneous array exhibits an overlapped bandwidth of 720 MHz and $360^{\circ } \times 108^{\circ }$ beam coverage at the 2.4-GHz band, which shows its superior performance and its huge potential in the mountainous and dense-forest communication applications.