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High Altitude Platforms may offer high spectrum efficiency by deploying multi-beam, multi-cell communications networks. The properties of the antennas carried by the HAP payload are key to the effective exploitation of these benefits. This paper compares different models for the antenna sidelobe region and quantifies, in each case, the carrier to interference ratio for a 3 channel re-use plan. Networks of 121 and 313 cells are compared. We show how the ITU recommended pattern for the 47/48 GHz band leads to pessimistic results compared to an adapted pattern which fits that of measured data for an elliptic beam lens antenna. The method is then extended to consider other radiation patterns. Spectrum sharing issues are explored with reference to further ITU recommendations and comparison with measurement data. Finally, an ITU type cellular layout which uses the same antenna for each cell is compared to an alternative hexagonal layout where each cell has equal size.

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In this paper, we describe intelligent beamforming antenna systems that can be used in the millimeterwave band for High-altitude platform systems. We have developed two antenna systems for the millimeter-wave band and have designed experiments to test the efficiency of the developed systems. One is a multi-beam-horn antenna that enables high-speed transmission, and the other is an array antenna that digitally controls antenna beams. These antenna systems are also designed to work in the stratosphere. We also describe our solutions to the problems of low temperature and low pressure and show that the two antenna systems can function well in the stratosphere through tests conducted on the ground.