In this book, the coverage of High-Altitude Platforms cellular system is analyzed and improved using antenna arrays and beamforming techniques. Firstly, the HAP cell footprint is analyzed and footprint equations are investigated that include the effects of the earth's curvature. Secondly, regarding the cellular layout expansion of HAPs, an algorithm is introduced for cells' beams pointing generation. Thirdly, the carrier-to-interference (CIR) in the HAP tessellated cell structure has been improved using uniform circular antenna arrays (UCCAs) with low-sidelobe levels. Fourthly, the wide area coverage of the HAP is effectively designed for long desert highways coverage using innovated cell shapes. This cell is called "Worm Cell" as it follows the terrains of the highways and has several advantages such as uniform received power along the highway, reduced radiated power in the unwanted regions, easy and flexible control of the cell pattern and length and reduced handoff and location updating rates.