Wang-Ik Son

Contactless Energy Transfer Systems Using Antiparallel Resonant Loops

Due to the convenience of using electronic devices, contactless energy transfer (CET) systems have garnered interest in various fields of industry. In this paper, a new design approach that uses antiparallel resonant loops for CET systems is presented. Forward and reverse loops forming an antiparallel resonant structure stabilize the transfer efficiency and therefore prevent it from dramatic distance-related changes, a phenomenon that can occur in CET systems with nonradiative methods (or resonant methods). This paper proposes frequency-insensitive antiparallel resonant loops and the optimal design of these loops for uniform transfer efficiency according to the distance. The proposed technique achieves frequency variation that is one-sixth that of conventional unidirectional loops, thus improving the power efficiency to a maximum of 87%. The improved performance of data transmissions for near-field communication is also verified.

RFID Reader Front-End Having Robust Tx Leakage Canceller for Load Variation

A novel front-end structure for ultra-high-frequency RF identification reader is proposed. The proposed front-end consists of a balanced coupler and four-port feed antenna system. The proposed balanced coupler structure has high transmit/receiver isolation feature and good insensitivity to load variations. The proposed four-port feed antenna system is applied for removing the coupling among antennas, which deteriorates the isolation. The proposed system is numerically analyzed and verified experimentally as well.

Design of Compact Quadruple Inverted-F Antenna With Circular Polarization for GPS Receiver

A compact quadruple inverted-F antenna (QIFA) with right-hand circular polarization for global positioning system (GPS) receiver is presented. The proposed QIFA consists of four spiral-shaped inverted-F antennas fed by a compact multilayered feed network. In order to improve the radiation efficiency of four-port feed antenna like QIFA, we analyze an optimum matching method considering both reflection coefficient at each port and the mutual coupling between ports simultaneously. Experimental results show that QIFA of size 10 x 10 x 12 mm3 has a 3-dB beamwidth of more than 130°, the peak gain of -1 dBic and the axial ratio under 2 dB.

Compact Integrated Antenna With Circulator for UHF RFID System

A passive UHF radio frequency identification (RFID) reader antenna with high transmit/receive isolation, which consists of two quadrifilar spiral antennas (QSAs) and the feeding networks, is proposed. The high isolation can be achieved by two concentric, circularly polarized antennas and 4-point feed circuits, which make the same circular polarization. The simulated and experimental results show that the transmit/receive isolation is more than 40 dB and the gains of two QSAs are 1.0 dBi for the inner QSA and 0.7 dBi for the outer QSA at the 910 MHz, respectively.

Reconfigurable 1

This letter presents a reconfigurable 1 × 4 power divider operated at 2.45 GHz. The proposed circuit has four power transmission states and is designed mathematically to satisfy matching conditions for each state. The experimental results for the transmission losses for each state are 1.2 dB ~ 1.9 dB while the isolations for non-path ports are greater than 25 dB and the reflection coefficients for each power transmission state are less than -20 dB at the target frequency.

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This paper proposes the printed square quadrifilar spiral antenna (QSA) for mobile RFID reader. A folded inverted-F antenna structure is used as a spiral to increase the impedance of QSA. Results show that the array antenna has obtained a sharp 3 dB beamwidth, high gain and good axial ratio.

4 Power Divider With Switched Impedance Matching Circuits

This letter presents a simple and innovative method for designing and optimizing two circularly polarized printed quadrifilar antennas (PQAs). The PQAs are operated at UHF RFID (902-908 MHz) and GPS (1575 MHz) and intended for use at a portable terminal. This new antenna system comprises two PQAs concentrically arranged, but electrically isolated. Each PQA comprises four inverted-F monopoles arranged orthogonally and excited with a phase difference of 90°.

Printed square quadrifilar spiral antenna for UHF RFID reader

This paper presents a dual-frequency (HF and UHF) antenna for handheld radio frequency identification (RFID) reader to embrace the benefits offered by both the UHF and HF RFID systems. In the HF (13.56 MHz) band, a spiral-shaped loop antenna is used and placed at the outmost region of the available space. In the UHF (915 MHz) band, a quadrifilar spiral antenna (QSA) is used because it is electrically small and features a low frequency shift by platform size and is placed in the center of the HF antenna. Measurements revealed that the antenna provides a quality factor of 56.5 in the 13.56 MHz and a gain of 2.5 dBic in the 920 MHz band.

Compact Dual-Band Printed Quadrifilar Antennas for UHF RFID/GPS Operations

A new printed square quadrifilar helix antenna (QHA) for circular polarization (CP) is proposed and experimentally investigated for the application as a GPS receiving antenna in frequency range of about 1.575 GHz. To increase the input impedance of QHA, we use the folded inverted-F antenna as a helix. Experiment results show that the proposed antenna has a 3-dB beamwidth of more than 120deg and a front-to-back ratio of more than 15 dB. Also, the proposed antenna shows the peak gain of -2.5 dBic and the axial ratio under 0.5 dB in wanted frequency band.

Dual-frequency antenna for HF/UHF handheld RFID reader

A module integrated antenna with circular polarization for a mobile UHF radio frequency identification reader is presented. In the proposed design, a reader module using a hybrid assemble technique is directly integrated inside the antenna. In order to compensate the degraded radiation efficiency of the reader antenna due to the module integration, a quadruple inverted-f antenna (QIFA), a type of four-port antenna like QIFA, is used. For the compact four-port antenna, we analyze the optimum matching method considering both the reflection coefficient at each port and the mutual coupling among ports simultaneously to improve the performance of the proposed module integrated antenna. Experimental results show that the proposed module integrated antenna of size 80 × 80 × 11.2 mm3 with the shielded module is well matched, and has the peak gain of 3.3 dBic and the axial ratio under 2.5 dB.