Chao-Wei Wang

A New Planar Artificial Transmission Line and Its Applications to a Miniaturized Butler Matrix

A miniaturized quadrature hybrid coupler, a rat-race coupler, and a 4 times 4 Butler matrix based on a newly proposed planar artificial transmission line are presented in this paper for application in ultra-high-frequency (UHF) radio-frequency identification (RFID) systems. This planar artificial transmission line is composed of microstrip quasi-lumped elements and their discontinuities and is capable of synthesizing microstrip lines with various characteristic impedances and electrical lengths. At the center frequency of the UHF RFID system, the occupied sizes of the proposed quadrature hybrid and rat-race couplers are merely 27% and 9% of those of the conventional designs. The miniaturized couplers demonstrate well-behaved wideband responses with no spurious harmonics up to two octaves. The measured results reveal excellent agreement with the simulations. Additionally, a 4 times 4 Butler matrix, which may occupy a large amount of circuit area in conventional designs, has been successfully miniaturized with the help of the proposed artificial transmission line. The circuit size of the Butler matrix is merely 21% of that of a conventional design. The experimental results show that the proposed Butler matrix features good phase control, nearly equal power splitting, and compact size and is therefore applicable to the reader modules in various RFID systems.

A Modified Quasi-Yagi Antenna With a New Compact Microstrip-to-Coplanar Strip Transition Using Artificial Transmission Lines

We present a modified quasi-Yagi antenna for use in WLAN access points. The antenna uses a new microstrip-to-coplanar strip (CPS) transition, consisting of a tapered microstrip input, T-junction, conventional 50-ohm microstrip line, and three artificial transmission line (ATL) sections. The design concept, mode conversion scheme, and simulated and experimental S-parameters of the transition are discussed first. It features a compact size, and a 3dB-insertion loss bandwidth of 78.6%. Based on the transition, a modified quasi-Yagi antenna is demonstrated. In addition to the new transition, the antenna consists of a CPS feed line, a meandered dipole, and a parasitic element. The meandered dipole can substantially increase to the front-to-back ratio of the antenna without sacrificing the operating bandwidth. The parasitic element is placed in close proximity to the driven element to improve impedance bandwidth and radiation characteristics. The antenna exhibits excellent end-fire radiation with a front-to-back ratio of greater than 15 dB. It features a moderate gain around 4 dBi, and a fractional bandwidth of 38.3%. We carefully investigate the concept, methodology, and experimental results of the proposed antenna.

Miniaturized Branch-Line Coupler with Harmonic Suppression for RFID Applications using Artificial Transmission Lines

A miniaturized branch-line coupler based on a newly proposed planar artificial transmission line (ATL) is presented in this paper for UHF RFID applications. This planar artificial transmission line consists of quasi-lumped elements and their discontinuities, and can synthesize microstrip lines with a wide variety of characteristic impedances and electrical lengths. The measurement results agree well with the simulation ones. The experiments demonstrate that the proposed hybrid has a compact size of 24.4 mm times 25.8 mm, or equivalently 0.12lambdag times 0.13lambdag at the operation frequency, 915 MHz. This corresponds to a 73% size reduction as compared to that of a conventional branch-line coupler. The wideband response reveals that the proposed hybrid is well-behaved with no spurious harmonics up to 11.1 GHz.

A planar quasi-yagi antenna with a new microstrip-to-CPS balun by artificial transmission lines

In this paper, we discuss a new design of quasi-Yagi antenna for 5 GHz WLAN applications. The antenna employs a new microstrip-to-CPS balun which is realized by a newly proposed planar artificial transmission line (ATL). This ATL is composed of microstrip quasi-lumped elements and their discontinuities. By simultaneously increasing the series inductance and shunt capacitance of the line section while keeping their ratio unchanged, microstrip lines with a wide variety of characteristic impedances and electrical lengths can be synthesized in a very compact form. To further improve the antenna front-to-back ratio, in this paper the dipole arms are meandered such that the truncated ground plane is relatively large compared to the radiator. The overall size of the antenna is 45 by 30 mm2. The antenna configuration, design methodology, and simulation results are investigated in detail in the following sections.

A Miniaturized Wilkinson Power Divider with Harmonic Suppression Characteristics Using Planar Artificial Transmission Lines

In this paper, a miniaturized Wilkinson power divider with harmonic suppression characteristics is proposed for ultra-high-frequency (UHF) radio frequency identification (RFID) applications. This design consists of four sections of a recently proposed planar artificial transmission line (ATL). The experimental results reveal that the proposed power divider features low insertion loss and compact size. At the center frequency of the UHF RFID system, the occupied size of the proposed miniaturized Wilkinson power divider is merely 13.4 mm X 22.4 mm, or equivalently 0.065 lambdag X 0.109 lambdag . By utilizing the harmonic suppression nature of the ATL and two additional short-circuited stubs, this miniaturized divider also exhibits harmonic suppression characteristics over nearly a decade bandwidth. The design methodology, simulated and experimental results are discussed throughout the paper.

A Miniaturized Diplexer Using Planar Artificial Transmission Lines for GSM/DCS Applications

In this paper, a new planar miniaturized diplexer is proposed for GSM/DCS dual band cellular phone applications. The design is composed of four sections of a recently proposed planar artificial transmission line (ATL) which is used to replace the conventional series quarter-wavelength transformers and the shunt open-circuited stubs. The experimental results reveal that the proposed diplexer features low insertion loss, high isolation and compact size. At the center frequency of the GSM system, the occupied size of the proposed miniaturized diplexer is merely 24.4 mm times 17.6 mm, or equivalently 0.119 lambdag times 0.086 lambdag . The design methodology, simulated and experimental results are discussed throughout the paper.

Phased Array Antenna for UHF RFID applications Using Artificial Transmission Lines

In recent years, ultra-high-frequency (UHF) radio frequency identification (RFID) systems have drawn more and more attentions in a wide variety of applications such as retail item management, access control system, electronic toll collection, and etc. By incorporating with a commercial RFID reader, it has been noted that the phased array antenna can be implemented in a RFID system to either control the interrogation region or to improve the successful tag identification rate. The switch-beam antenna, which is capable of sequentially steering the radiation beam to certain pre-defined spatial directions for given periods of time, can be applied to improve the successful tag identification rate since the tags to be interrogated in such an arrangement can be illuminated by higher transient RF power. By utilizing the switch-beam antenna array, it is believed that the carrier-to-interference (C/I) ratio of a RFID system can be substantially improved along the direction to which the mainbeam of the antenna array illuminated.

A miniature GPS planar chip antenna integrated with low noise amplifier1

A planar chip antenna integrated with a low noise amplifier (LNA) for GPS applications at 1.575 GHz is presented in this paper. Software packages, XFDTD and HFSS have been applied to design the chip antenna having dimensions of 10 mm (L) times 8 mm (W) times 0.8 mm (H). An insert molding approach is applied to manufacture the antenna, where meandered metal strips are enclosed with liquid crystal polyester (LCP) to form the chip antenna. Thus, this chip antenna comprises a radiating structure of multiple meandered conducting strips packed with an LCP dielectric composite material to achieve size, performance characteristics and cost effectiveness superior to conventional GPS ceramic patch antennas. The compact surface-mount chip antenna is fully compatible with hand- and reflow- attachment processes. Also, no additional impedance-matching circuit is required so that the occupied length of the antenna built in a GPS receiver operating at 1.575 GHz is just 10 mm.