Improving the cellular coverage from a high altitude platform by novel tapered beamforming technique

In wireless communications utilizing high altitude platforms, the cellular coverage depends on the sidelobe level of the used antennas which affects the carrier-to-interference ratio (CIR). Many antenna configurations are applicable but antenna arrays are more flexible than spot-beam antennas. Therefore, this paper proposes a beamforming technique based on tapering the array feeding currents with a Gaussian function for sidelobe reduction. The antenna array configuration is chosen as the uniform concentric circular arrays (UCCA) and the simulations for a HAP cellular system consisting of 69 cells shows that the CIR may reach 43 dB at the cell center and about 20 dB at the cell edge for a typical cluster size of four. The innovated beamforming technique applied to UCCA is compared with other conventional array configurations such as square two-dimensional arrays (TDA) showing an increase of the CIR by 13 dB at the cell edges and about 26 dB at the cell center.