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 Title: Small, dual band, placement insensitive antennas Author(s): Ruyle, Jessica Director of Research: Bernhard, Jennifer T. Doctoral Committee Member(s): Cangellaris, Andreas C.; Franke, Steven J.; Kudeki, Erhan Department / Program: Electrical & Computer Eng Discipline: Electrical & Computer Engr Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Slot Antenna RFID Antenna Placement-Insensitive Antenna Dual-Band Antenna Edge Treatment Radio-frequency identification (RFID) Abstract: RFID systems with peel-and-stick'' labels are currently limited to tracking items with nearly electromagnetically transparent material properties. This limitation stems from the antenna choice for these labels - a dipole variant. The slot antenna, the effective inverse of the dipole, is shown to be an effective RFID antenna for environment-independent peel-and-stick applications. A miniaturization and multi-band design technique is shown for a placement insensitive RFID antenna. With the significant advance in functionality over existing RFID antennas that is demonstrated by the antenna discussed in this dissertation, the purview of peel-and-stick RFID systems can expand to track all object types (metal, liquid, etc.), overcoming a fundamental limitation in current RFID deployments. A traditional straight half-wavelength slot antenna would be too large for an RFID antenna at commonly used RFID frequencies. We investigate loading the slot antenna to reduce its size. By end-loading the slot, the total size of the slot can be greatly reduced. If the slot antenna is correctly loaded for a particular frequency, the input impedance seen at the feed point is the same for the full-sized or loaded slot. If an effective length of less than a half-wavelength is desired for the slot, the loads should be inductive. A slotline inductor provides an easily integratable inductance for the slot antenna and is used for the present antenna design. Loading the slot with a slotline inductor also provides the ability to make the antenna multi-band since the impedance of the inductor changes with frequency. To ensure that the performance of the miniaturized slot antenna is independent of the material to which it is attached, a reflecting plane is added to the design. However, slot antennas with closely spaced reflectors often couple energy into a parallel plate mode between the ground plane and the reflecting plane. The parallel plate becomes a cavity with the walls appearing as reactive loads to the slot antenna. In this work, we show that edge serrations can reduce the cavity effect in a parallel plate configuration, making a slot antenna with edge treatments a viable design for environment-independent peel-and-stick applications. For this research to be broadly applicable, transmission line models are pursued to aid in the design process. Transmission line models for a rectangular and circular slotline inductor are presented as well as a model describing edge serrations on the ground plane in a parallel plate configuration. Each of these models is useful in and of itself, and they are combined in this research to present a design methodology for placement insensitive peel-and-stick RFID antennas. This methodology is used for the design of an antenna with a peel-and-stick'' form factor, and the antenna is shown through measurements to be placement insensitive - displaying no observable change in input impedance for different backing objects. With the discussed design methodology, different antennas can be designed for many different frequency bands and applications within RFID and any other application that requires an antenna that fits within a thin form-factor. Issue Date: 2012-02-01 Genre: thesis URI: http://hdl.handle.net/2142/29541 Rights Information: Copyright 2011 Jessica E. Ruyle Date Available in IDEALS: 2014-02-01 Date Deposited: 2011-12
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