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In this paper, a metal-backed loop antenna (MBLA) at high frequency (HF) is characterized and applied to a radio-frequency identification (RFID) smart-shelf system. The antenna is investigated in terms of impedance matching, resonant frequency, magnetic-field intensity/field distribution, quality factor, and detection range. The study shows that the magnetic-field distribution of the metal-backed loop antenna can be effectively controlled by changing the size as well as the separation of the backing metal plate. As a result, the detection range of an RFID system using such an antenna can be controlled. Such a feature offers great promise for the metal-backed loop antenna in applications for RFID smart-shelf systems. For such systems, controlling the coupling zone of the antennas is vital for constraining the interference between the antennas in adjacent tiers of the shelves, in order to achieve high system-detection accuracy. In addition, using a metal-backed loop antenna provides more flexibility for RFID smart-shelf-system design and implementation, so that the system is more cost effective. [ABSTRACT FROM AUTHOR]

Frequency-swept input-impedance measurements to determine Q factors and field strengths for an electrically small tuned transmitting loop antenna in its operating environment have recently been made. These observational results are compared with numerical modeling by the computational electromagnetic code NEC-4D, since the validity of this code to simulate the performance of electrically small loops - and, in fact, even the fundamental characteristics of small loop antennas - has been questioned. [ABSTRACT FROM AUTHOR]

The performance of a typical small loop antenna of I m diameter is presented at frequencies in the range 3.6-10.1 MHz. It is argued that the antenna may reasonably described as electrically small in this frequency range. Measurements of the antenna's bandwidth and, hence, Q factor are presented, along with direct measurements of the radiated field at various distances with a carefully measured RF input power. The radiation efficiency of the loop is derived from the measurements, and is compared with theoretical predictions of the efficiency based on classical electromagnetics. Close agreement is demonstrated between measurements and predictions. Consistency with the Chu bandwidth limit is also demonstrated for this antenna. [ABSTRACT FROM AUTHOR]