A Balloon Conformal Array Antenna of Broadened Bandwidth, High Gain, and Steerable Directional Beam Fed by a Flexible Phase Shifting Network

This article presents, for the first time, a balloon-based conformal array antenna for emergency communication applications in low-range hilly forest scenarios. Fed by a simple, flexible phase shifting network, the antenna features broadened bandwidth, high gain, and steerable directional beam, outperforming other electrically thin conformal array antennas in terms of comprehensive performance. The basic array element is a cylindrically conformal microstrip patch antenna, whose bandwidth is widened by adding parasitic patches loaded by shorting pins for size miniaturization and mutual coupling reduction. Then, a $1 \times 4$ conformal subarray with parallel feeding network is designed and optimized for beam sharpening in the elevation plane. To further increase the gain and enable beam steering for full azimuthal coverage, the balloon is surrounded by multiple $1 \times 4$ conformal subarrays, and only four of them operate at a time. A flexible phase shifting network is designed for beam steering along the azimuthal direction. To validate the effectiveness of the designs, a prototype was fabricated and measured. Experimental results show the antenna exhibits a gain of around 15 dB and a bandwidth of 74 MHz at the 2.4 GHz band, which has demonstrated the good performance of the balloon conformal array antenna and its huge potential in low-range hilly forest communication applications.