Comparative performance assessment of a mobile satellite communications system exploiting a frequency-scanning satellite antenna

The main property of a linear Frequency-Scanning (FS) antenna is that its maximum-gain azimuthal bearing varies proportionally to signal frequency. In a mobile communications system utilizing a FS on-board antenna and operating on Single-Channel-Per-Carrier (SCPC), all mobile users can virtually be served with the peak antenna gain, provided that the appropriate SCPC carrier frequency is assigned to each user. This represents a significant advantage with respect to systems utilizing the more conventional Fixed-Beams (FB) antenna approach, which results in a signal loss of up to 3 dB affecting mobile users located away from beam center. In the above promising perspective, a study activity was funded by the European Space Agency with the main aim to understand the overall merits of the FS and FB antenna concepts with regard to an L-band geostationary mobile communications system, by performing a system-level comparative trade-off. Particular efforts were devoted to assessing the influence of different traffic distributions, which may result in the concentration of mobile users in selected portions of the service area. This paper concentrates on the system-level results achieved in the course of the above mentioned study activities, technological issues being dealt with in other