An EVA antenna sampling and switching system for space station communication

The design of an EVA (extravehicular activity) antenna sampling and switching system is presented. The system utilizes four separate antennas for full spherical coverage with a space station. The antennas are placed at optimal locations on the back-pack of the EVA astronaut for best coverage performance. Continuous power-level monitoring of the four antennas results in the selection of the best antenna (the one receiving the highest signal level) for communication purposes. The system consists of four log conical spiral antennas, two single-pole-four-throw PIN diode switches, and a double conversion sampling channel that feeds a peak-level detector. A microcontroller algorithm cycles the sampling and switching of antennas based on the level detector output. Attention is given to the block diagram of the system, the development of in-house components, the control algorithm, and the results of composite antenna pattern testing. Measured composite patterns are compared to a computer-synthesized composite pattern derived from individual antenna patterns.<>