(A) study on the mobile satellite multimedia antenna with novel hybrid beam scanning scheme

Abstract

Reflector antennas with mechanical beam scanning occupy an important place in the field of mobile communication systems. But the mechanical beam control method has the essential shortcoming of limited beam scanning speed. Thus the phased array antennas using the electrical beam scanning method have been widely developed these days. But the phase array antennas has the problem in commercial applications that they are very expensive compared with the mechanical tracking antennas because of the many active components such as amplifiers, phase shifters and so on. Thus the hybrid antenna (HA) has been proposed to overcome the problems and is a good candidate if rapid beam steering in a relatively small angle sector is needed. The HA has the hybrid composition of an antenna such as ‘reflector + phased array’ and possesses the merits of both the reflector antenna and phased array antenna. The sufficiently large aperture of the reflector provides the high gain typical of the reflector antenna, and the compound feed (such as a small phased array antenna) provides electrical beam scanning in a narrow angle sector. Thus, the HA is a reasonable compromise between a highly efficient but non-scannable reflector antenna, and a compound and expensive phased array antenna that provides electrical scanning. A small quantity of control elements in the hybrid antenna’s array and its small size in combination with the light and cheap reflector in some cases, can help minimize the cost and size of the antenna system. In this thesis, a HA with a novel hybrid beam scanning scheme is proposed. This antenna has a Cassegrain structure composed of two reflectors and a feeder. The parabolic-shaped main reflector is designed for high gain, while the subreflector is rotational and flat. The feeder is a phased array with arbitrary shaped aperture and 20 element antennas. The HA is capable of two-dimensional beam steering by means of two operations: rotation of the subreflector and phase con...