專用短距通訊車裝通訊設備之設計與量測

Abstract

本論文研發完成一組5.8GHz 被動式專用短距通訊車裝通訊設備答詢器，面積約為12.5 ×5.5 cm2 ，此答詢器採雙面天線與電路之結合製作，正面為圓極化微帶天線及二進制幅度鍵控電路設計，背面為孔隙天線、混波降頻電路與一組8位元二進制編碼電路。為節省電源，本答詢器採被動設計，答詢器上所包含四個相同圓極化之微帶天線，其饋入線採廣角回波設計，兩兩一組形成兩組廣角回波天線，而天線上各有一雙向之二極體開關，此開關同時由背面之編碼電路所控制。當路旁通訊基地台發射出訊號，第一個資料封包為下載鏈結時段，此時所發射之幅度鍵控調變訊號可由答詢器背面之孔隙天線、混波降頻電路及比較器所解碼，接下來就為資料上傳鏈結時段，通訊台發射出的連續未調變訊號由每一個天線收到微帶線上，經由幅度鍵控調變後再輻射回基地台進行解碼之工作。由於採廣角回波之設計，四個天線再輻射回通訊台的電磁波可同相相加，因此此答詢器回波強度可較傳統單一天線答詢器回波強度高 12dB，訊號雜訊比(SNR)增加6dB，可提高答詢器之答詢距離及靈敏度。

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