超高頻無線射頻辨識系統，因其讀取距離較長，所以容易受到多重路徑衰減的影響，本論文提出符合台灣超高頻無線射頻辨識操作頻段規範之925MHz多輸入多輸出被動式射頻辨識標籤，以改善此問題。
本論文使標籤接受來自於不同極化方向的發送訊號，量測標籤兩天線分別回傳的能量大小，由實驗量測結果驗證多輸入多輸出超高頻被動射頻辨識標籤對於多重路徑衰減下之改善效果。
標籤架構參考林旺旗學長於論文中所設計之雙天線半被動式射頻辨識標籤及無線識別與傳感平台(Wireless Identification and Sensing Platform, WISP)中之類比前端電路架構，進而優化為多輸入多輸出架構，並於標籤端上增加對於接收訊號強度(Received signal strength indicator, RSSI)之量化功能，並將量化後數值利用空-時區塊編碼技術（Space-Time Block Code, STBC）回傳給讀取器端，以便實驗量測分析。
此外由於標籤改進回傳格式不同，故無法使用舊有讀取器用於實際運算分析，故於實驗上採用觀察量測能量變化，用以驗證標籤實際之效果。

Due to the long read range, the performance of Ultra High Frequency (UHF) Identification (RFID) system can be easily affected by multi-path fading. To overcome the preceding problem, a MIMO UHF passive RFID tag, operating at 925 MHz, complied with the regulation of Taiwan, is proposed in this thesis.
With different polarizations of transmitter, we measure the tag backscatter power .The experimental results verify the effects of tag against multi-path fading.
The structure of the dual antenna tag is referred to the structure of analog front-end circuit of Wireless Identification and Sensing Platform (WISP) and the 　semi-passive dual antenna tag design in Lin’s thesis and optimized becoming a passive dual antenna tag. Furthermore, we add the quantization function of Received Signal Strength Indicator (RSSI) on MSP430. Thus, the quantized values can be transmitted to receiver by Space-Time Block Code, STBC.
In addition, because of the difference pattern of backscatter of the improving tag, compared with tag proposed by previous literature, the reader we used before is not available to analyze the data. Therefore, the effects are verified by measuring, observing and analyzing the energy variation.

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