NTT Technical Review, September 2005, Vol. 3, No. 9

The recent exponential growth of high-speed Internet connections has created a huge demand for ubiquitous access links to the Internet, and mobile Internet services on cellular or wireless LAN networks have increased rapidly. A major role of mobile satellite communication networks is to provide ubiquitous broadband services. The target users of these services are people who do not have access to terrestrial networks, such as passengers on ships, airliners, and trains. The satellite network we envisage uses the Ku-band (14/12 GHz) and has an onboard antenna diameter of about 1 m to handle broadband services with bit rates of several tens of megabits per second. The Ku-band is primarily allocated to fixed satellite services, so the transmitting antenna system must have the same pointing accuracy as fixed earth stations. ITU-R*1 established the technical constraints on the pointing errors and other antenna attributes for earth stations onboard vessels (ESVs) in WRC*2 2003 [1]. The antenna pointing error of the mobile terminals in narrowband systems for mobile satellite services, such as Inmarsat [2], is a few degrees [3]. In contrast, the pointing accuracy requirement for ESV antennas is 0.2° peak [1], one order of accuracy higher. This level of accuracy usually demands extremely accurate sensors, such as ring laser gyros (RLGs), which greatly increase the antenna system costs. There have been very few studies on shipboard antenna systems that can accommodate the ITU-R restrictions at a relatively low cost. Taylor [4] uses two mechanical gyros to stabilize the antenna platform. The basic principle of stabilization is that the inertial wheel can maintain a constant direction while the ves-