| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 96 === In this thesis, we discuss the influence of the reflection coefficient on the backscattered fields of the tag antenna. In addition, the measurement result of backscattered fields is consistent with the result calculated by theoretical analysis. Next, we apply the above results in a novel tag structure for RFID system. This novel structure contains two antennas: one is designed to match the tag IC for maximum power transfer, and the other is alternatively switching between “open” and “short” to achieve maximum difference between backscattered fields. Based on this fact, when designing the impedance of backscattering antenna, the ratio of the imaginary part to the real part is suggested to be as small as possible.
Moreover, we extract the actual waveform backscattered from the tag and apply the coherent detection method. Although the detection result is better than the detection result adopted in commercial products, but it is not as good as expected. We found that the increase in the probability of false detection is a result of the high-pass filter inherent in the reader structure. According to this high-pass effect, we proposed a modified coherent detection method. Simulation and measurement results verify that the proposed modified coherent detection method can reduce the detection error probability.
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