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Advanced Chipless RFID by Chamath Divarathne, Mohammad Zomorrodi, Nemai Chandra Karmakar

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CHAPTER 6SAR-BASED SIGNAL PROCESSING

6.1 INTRODUCTION

It was already discussed that it is possible to provide a fine spatial diversity for data encoding purpose in a chipless radiofrequency identification (RFID) system by utilizing the millimeter-wave bands of 60 GHz and above. However, considering the reading range, tag size, and expected data encoding capacity, it is not technically possible to use one single antenna at the reader and expect the millimeter resolution on the tag surface. Instead, a synthetic aperture length of 15–30 cm can be constructed by a small moving antenna. The signal processing based on the synthetic aperture radar (SAR) technique then provides a spatial diversity of millimeter order at the tag surface.

This chapter reviews the SAR-based signal processing for the proposed chipless application. Given that the SAR technique is a mature field of research with very wide applications, the very basics of the SAR will be reviewed here and readers can refer to the appropriate books in this field [1]. The spotlight mode of operation will be applied for the proposed application for tag data decoding purpose.

First a sample tag with only 4 data bits capacity is considered for the proof of concept. The effect of synthetic aperture size on the achievable spatial resolution is discussed as well. In the final section of this chapter, the ultimate encoding capacity of the proposed technique is considered based on the maximum allowable tag surface. A tag that is 5.5 ...

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