Chihyun Cho

Design of a Circularly Polarized Tag Antenna for Increased Reading Range

We introduce a novel circularly polarized tag antenna, consisting of a truncated patch, a shorting plate, and a ground plane, to increase the reading range while remaining in compliance with EIRP regulations. The reading range of the proposed tag is twice that of linearly polarized tags, due to the decreased polarization mismatch between the reader and tag antennas. An additional parasitic patch is loaded onto the structure to boost the reading range in the UHF RFID band. As a result, an average reading range of 8 m is achieved between 860 MHz and 960 MHz, compared to a range of about 3 m with conventional dipole tags.

Design of UHF small passive tag antennas

We explore structures of planar tag antennas that permit high efficiency, a low profile, and reliable performance on a variety of dielectric materials. For the basic structure of the antenna, we used the inductively coupled feed concept to efficiently reduce the size of the tag antenna. We examined two different types of windings for the antenna body to achieve better performance with the given RFID tag chip. To find detailed design parameters that attain multiple design goals, we employ a Pareto genetic algorithm with an IE3D of Zealand EM simulator. The finalized designs were built on a 5 mil thick Duroid substrate with the Alien tag chip. The size of the optimal design was reduced to kr=0.2, with a readable range of 40 cm-280 cm.

Planar Near-Field RFID Reader Antenna for Item-Level Tagging

In this letter, we propose a novel UHF planar near-field antenna for the application of RFID item-level tagging. The proposed antenna was designed to have a strong and uniform Hz-field over a broad antenna aperture to identify the various items with stable reading performance. To obtain a strong near Hz-field, two coupled patches are employed along with a microstrip-line feed, resulting in average Hz of -15 dBA/m on antenna aperture (30 × 30 × 10 cm3). We also measured the reading range, and it confirmed that the proposed antenna is suitable for a commercial RFID smart-shelf application.

Design of Novel RFID Tag Antennas for Metallic Objects

In this paper, a novel tag antenna is proposed; it has a very simple structure that does not require a ground plane or shorting pins. The proposed tag antenna has significant advantages over other types of tag antennas for metallic objects, such as low cost, light weight, and ease of fabrication. The body of the antenna is printed as a single planar strip line on a thin PET substrate (polyethylene, epsir =3.9, tandelta=0.003) and it is mounted on foam substrate (epsir=1.0). The detail design parameters of the proposed antenna were optimized using the Pareto genetic algorithm (GA) in conjunction with the IE3D EM simulator and the resulting tag antenna has readable ranges of about 2.8 m when mounted in the air and 1.8 m when mounted on a metallic surface

A Modified Wheeler Cap Method for Efficiency Measurements of Probe-Fed Patch Antennas With Multiple Resonances

We propose a modified Wheeler cap method to accurately measure the radiation efficiency of patch antennas with multiple resonances by modeling their impedance as a high-order circuit model. The radiation efficiency is obtained from the power consumption ratio between the radiation and loss conductances using a circuit model we developed. Our technique is validated by measuring the efficiencies of a circularly polarized microstrip patch antenna and a triple-band microstrip patch antenna. The measurement results are in close agreement with those produced by simulations, whereas the Wheeler cap method with a series-(or parallel-) resonant circuit model is shown to be unreliable.

The Effects of Substrate, Metal-line, and Surface Material on the Performance of RFID Tag Antenna

We investigated the effects of substrate, metal-line, and surface material on the performance of radio frequency identification (RFID) tag antenna using a tag antenna with a meander line radiator and T-matching network. The results showed that readability of the tag antenna with a thin high-loss substrate could be increased so that it was similar to that of a low-loss substrate if the substrate was very thin. The readability of the tag antenna decreased significantly when the metal line was thinner than the skin depth. The readability of the tag also decreased drastically when the tag was attached to high-permittivity high-loss target objects.

Planar near-field RFID reader antenna using opposite-directed currents

In this paper we propose a novel planar near-field antenna for radio-frequency identification (RFID) based on the principle that two closely spaced opposite-directed currents (ODC) can generate a strong magnetic field over a broad surface area. To implement the ODC concept, the proposed antenna uses a dipole and a parasitic patch with a microstrip feedline. The proposed antenna provides an Hz field greater than −20 dBA/m in a region of 30 × 30 cm2. Measurements with a commercial RFID system show a maximum reading range of 24 cm, and a reading area of 744 cm2 for a reading range greater than 5 cm.

W-Band Permittivity Measurements Using a Free-Space Material Measurement Technique

In this paper, a free-space material measurement technique is discussed in W-band(75~110 GHz). For the accurate measurement of S-parameters of an MUT(Material Under Test) in free space, a W-band quasi-optical free-space material measurement system, less affected by the measurement environments, is discussed, and GRL(Gated Reflect Line) method for calibrating the measurement system is described. Proposed technique is verified for `Air` and measurement results for arystal plates of thickness 1.1 mm, 2 mm, 2.75 mm and 5 mm are also shown.

Improved Wheeler Cap Method Based on an Equivalent High-Order Circuit Model

The conventional Wheeler cap method usually produces accurate radiation efficiency of small antennas when the antennas under test (AUTs) operate as a simple series or a parallel RLC resonance circuit. However, this method often gives unreliable radiation efficiency if the AUT has a complicated operating principle such as circular polarization (CP), multiple resonances, or broad-band properties. In this paper, we propose an improved Wheeler cap method based on the equivalent high-order circuit model including transformers to provide accurate radiation efficiency, although the AUT does not operate as a simple resonance circuit. For building equivalent high-order circuit models, a method for estimating the initial values of a genetic algorithm (GA) is also proposed, which effectively reduces the searching space and improves the convergence of the optimization. To verify the proposed method, we measure the radiation efficiency of a CP microstrip antenna, a UHF RFID tag antenna, and a triple-resonance microstrip antenna.

U-Shaped Broadband RFID Tag Antenna with a Parasitic Element

PURPOSE: An U-shaped broadband RFID tag antenna with a parasitic element is provided to obtain uniform recognition distance of a frequency in wireless by inserting parasitic element into the dipole antenna of U shape. CONSTITUTION: A dipole antenna(120) comprises a first conductive wire and a second conductive wire connected to the first conductive wire. A power feeding unit(140) is connected to the second conductive wire. First parasitic conductive wires(p122) are located inside the dipole antenna and have an 11 width while being separated from each other by a 11 distance.