被動式汽車短距離通訊微波答詢器之研發

Abstract

本本論文研發完成一組5.8GHz被動式汽車短距通訊答詢器，面積約在14.5×7.5 。此答詢器結合圓極化微帶天線及二進制幅度鍵控電路設計完成。答詢器採被動式設計，以節省所需電源。答詢器上包含四個相同圓極化之微帶天線。天線之饋入線採廣角回波式設計，即外圍兩天線以微帶線連接成一對、中間兩天線亦以另一微帶線連接成對。兩微帶線長度相同，線上各有一雙向之二極體開關，兩個開關由同一個二進制加碼電路控制。路旁通訊台發射出的訊號由每一個天線接收到微帶線上，經加碼後直接饋入到同對之微帶天線上，再輻射回基地台。由於採廣角回波設計，四個天線再輻射回通訊台的電磁波可同相相加，因此本計畫設計的答詢器回波強度，在不增加電源消耗的情況下，將較傳統答詢器的回波強度高12 dB左右，如此可大幅提高答詢器的答詢距離及靈敏度。

In the thesis, a 5.8GHz passive transponder for vehicle short-range communications is developed. The transponder is composed of 4 circularly polarize(CP) microstrip antennas and binary amplitude shift keying (ASK) modulation circuits. The transponder uses a passive design, which enhancing the transponder echo. The overall size of the transponder 14.5×7.5 . The Van Atta retrodirective array design is used for the routing of the antenna feed lines. The two peripheral antennas are paired by a microstrip line, and the middle two are paired by another microstrip line with the same length. There is a bilateral diode switch on the way of each microstrip line, both of which are controlled by a binary encoding circuit. The signal received by each antenna, after encoded, is directly fed to the antenna of the same pair and is then re-radiated to the roadside beacon. Due to the retrodirective design, the fields re-radiated from the four antennas are coherently added at the interrogator (beacon) direction, so that, without increasing the consumed power, the transponder echo of the present design has a strength 12dB higher than those of the traditional transponders. Thus, the communication range and the sensitivity can be enhanced greatly.