Citation
Abstract
On both ends of an in situ ultra-high frequency (UHF) link, multipath signal reflections—characterized by signal reflection, diffraction, and blockage—can cause a significant drop in link performance. The purpose of this article is to study the extent and effects of multipath signal reflections, explore possible strategies, and provide recommendations for mitigating multipath for communications over a relay link. The performance of telecommunications over a relay link with different antenna options on both ends was studied. Results of our analysis and simulations indicate that keeping the antenna pattern symmetric is important. It was shown that data-return volume for a Smart Lander communicating with Odyssey increases over 2.6 dB if the monopole antenna is placed on the equipment deck rather than on the solar arrays. In similar scenarios, data-return volume improves some 0.4 dB if a cross-dipole antenna is used on the rover instead of an equipment-deck-mounted monopole antenna on the rover. The reason is that horizontally/circularly polarized antennas reduce the coupling to the vertical scatterers on the rover and hence maintain a more symmetric pattern on different locations of the rover. In summary, the spacecraft layout and antenna placement should strive to minimize impacts that would create antenna-pattern asymmetry. The effects of Mars’ environment on the relay uplink performance also was studied. Received signal-power variations as a function of satellite elevation angle and azimuth angle were calculated for the Mars Exploration Rover (MER), located in Martian open, flat terrain and Martian hilly terrain, communicating uplink to the spacecraft. It was shown that despite the monopole and cross-dipole discrimination against multipath, signal variation can reach −13 dB at elevation angles between 5 and 15 deg. Cross-dipole antennas impose more discrimination at low elevation angles than do monopole antennas. It was observed that using a cross-dipole antenna instead of a monopole antenna on MER decreases signal variation, especially at larger elevation angles.
Keywords
Details
- Volume
- 42-151
- Published
- November 15, 2002
- Pages
- 1–21
- File Size
- 551.7 KB