Space station GPS antennas multipath analysis

In this paper, the magnitude and phase of the Global Positioning System (GPS) signals with multipath interference from space station structures are computed using the geometrical theory of diffraction (GTD). Obtained results indicate that reflections from and diffractions around the space station structures in the vicinity of the GPS antennas can produce larger than 10 mm phase shift. The multipath effects are more evident in the phase shift patterns than in the gain patterns. This demonstrates that the phase variations are more sensitive to multipath than the gain variations. Results also show that significant phase shifts of greater than 10 mm, due to multipath from other objects, are possible in the unobscured antenna boresight region where gain levels are high. In general, the phase shift caused by multipath is a function of the indirect-to-direct signal strength ratio and the path length difference between the indirect and direct signals. To minimize multipath, the GPS antennas should be placed so that the blockages and reflections from the space station major structural elements are minimized.