| Summary: | 碩士 === 國立交通大學 === 電信工程系 === 88 === In the thesis, a 5.8 GHz passive On-Board Unit (OBU) for the Dedicated Short-Range Communication (DSRC) is developed. The front side of the two—side OBU consists of 4 left-circularly polarized (LCP) microstrip antennas and binary amplitude shift keying (ASK) modulation circuits; the back side of the OBU contains a slot antenna, a mixing diode circuit, and a 8-bits binary encoding circuit. To enhance the battery life, the OBU is designed as a passive one with a size of about 12.5 ×5.5 cm2.
The Van Atta retrodirective array design is used for the routing of the antenna feed lines. On the path of each microstrip line is a bilateral diode switch controlled by the encoding circuit output from the back side of the OBU. During the downlink, the encoding signal sent from the roadside unit (RSU) is received by the slot antenna, and decoded by the mixing diode circuit. During the uplink, the RSU sends a continuous wave to the OBU. The wave received by each antenna of the OBU, after encoding, is directly fed to the antenna of the same pair and is re-radiated to the RSU to be decoded. By the retrodirective design, the field radiated back to the RSU from the four antenna elements is coherently added. The echo strength is 12dB, and the signal-to-noise ratio (SNR) is thus 6dB, higher than the conventional one-antenna-element design
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