Phase steering for modified dodecahedral array for mobile satcoms

Satellite communication to a mobile unit such as a Landrover, which may be moving over quite rough terrain, represents a challenge to the antenna designer. The signal has to be received over the full upper hemisphere, with allowance for the fact that the antenna platform may be tilted at any time by up to 20 uˆ in any direction. The signal should be received with much the same strength whatever the orientation, and also a substantial antenna gain (of the order of 20 dB) is also desirable, at a carrier frequency of about 8 GHz. A spherical array antenna seems a good starting point for the design, though not quite the whole sphere would be needed, but this would not lend itself conveniently to an advantage that planar arrays, for example, have of allowing modular design, including the use of printed circuit technology. This permits a useful number of elements to be combined on a module (or tile) reducing the array cost substantially. A close approximation to a sphere is given by the regular solids of the icosahedron (20 triangular faces) or the dodecahedron (12 pentagonal faces). The full array would then consist of 60 identical triangles each carrying six elements, but in fact the lowest faces are not required and only 40 are used. We consider how the relative phase of the signal at each element can be determined systematically for this relatively complex array, in order to steer it, for transmission or reception. The link uses circular polarization, and this is a further complication in the steering phase computation