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Author

Chang-Fa Yang

Other affiliations: Ohio State University
Bio: Chang-Fa Yang is an academic researcher from National Taiwan University of Science and Technology. The author has contributed to research in topics: Antenna (radio) & Antenna measurement. The author has an hindex of 19, co-authored 87 publications receiving 1468 citations. Previous affiliations of Chang-Fa Yang include Ohio State University.


Papers
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Journal ArticleDOI
TL;DR: A coplanar waveguide (CPW)-fed planar monopole antenna with triple-band operation for WiMAX and WLAN applications is presented in this article, which occupies a small size of 25(L) × 25(W) × 0.8(H) mm3.
Abstract: A coplanar waveguide (CPW)-fed planar monopole antenna with triple-band operation for WiMAX and WLAN applications is presented. The antenna, which occupies a small size of 25(L) × 25(W) × 0.8(H) mm3, is simply composed of a pentagonal radiating patch with two bent slots. By carefully selecting the positions and lengths of these slots, good dual stopband rejection characteristic of the antenna can be obtained so that three operating bands covering 2.14-2.85, 3.29-4.08, and 5.02-6.09 GHz can be achieved. The measured results also demonstrate that the proposed antenna has good omnidirectional radiation patterns with appreciable gain across the operating bands and is thus suitable to be integrated within the portable devices for WiMAX/WLAN applications.

214 citations

Journal ArticleDOI
10 Dec 2007
TL;DR: In this article, a planar artificial transmission line is proposed for UHF radio-frequency identification (RFID) systems, which is composed of microstrip quasi-lumped elements and their discontinuities.
Abstract: 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.

195 citations

Journal ArticleDOI
TL;DR: In this paper, a planar monopole antenna with standard band-notched characteristic suitable for ultrawideband (UWB) applications is presented, consisting of a square slot patch with a vertical coupling strip, only occupying a small size of 15 (L) × 15 (W) × 1.6 (H) mm3.
Abstract: A compact planar monopole antenna with standard band-notched characteristic suitable for ultrawideband (UWB) applications is presented. This microstrip-fed antenna, consisting of a square slot patch with a vertical coupling strip, only occupies a small size of 15 (L) × 15 (W) × 1.6 (H) mm3. By properly designing the strip placed at the center of the patch, good frequency rejection performance of the antenna with a wide operating band from 3.05 to 11.15 GHz can be obtained. Compared to other designs, the antenna has a quite simple structure to make the band-notched property to reduce the effect caused by the frequency interference. Furthermore, fairly good omnidirectional radiation patterns and transmission responses both indicate that the proposed antenna is well suited to be integrated within various portable devices for UWB operation.

141 citations

Journal ArticleDOI
TL;DR: In this paper, the dielectric constant at high frequency, 1-M-1-GHz, increases with the solid content of barium titanate and diaminodiphenyl methane (DDM).

80 citations

Journal ArticleDOI
TL;DR: In this article, a periodic moment-method solution for scattering from a doubly periodic array of lossy dielectric bodies is developed to improve the performance of anechoic chamber measurements.
Abstract: A periodic moment-method solution for scattering from a doubly periodic array of lossy dielectric bodies is developed. The purpose is to design electromagnetic wedge and pyramidal absorbers for low reflectivity so that one can improve the performance of anechoic chamber measurements. The spectral-domain formulation and the moment-method volume polarization current approach are used to obtain the expressions for determining the scattering from a doubly periodic array of lossy dielectric bodies. Some wedge and pyramidal absorber configurations that have been designed, fabricated, and tested in the OSU/ESL compact range measurement facility are presented. By taking into account the complexity of real-world material structures, good agreement between calculations and measurements has been obtained. >

73 citations


Cited by
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Journal ArticleDOI
TL;DR: An impulse-response characterization for the propagation path is presented, including models for small-scale fading, and it is shown that when two-way communication ports can be defined for a mobile system, it is possible to use reciprocity to focus the energy along the direction of an intended user without any explicit knowledge of the electromagnetic environment in which the system is operating.
Abstract: In order to estimate the signal parameters accurately for mobile systems, it is necessary to estimate a system's propagation characteristics through a medium. Propagation analysis provides a good initial estimate of the signal characteristics. The ability to accurately predict radio-propagation behavior for wireless personal communication systems, such as cellular mobile radio, is becoming crucial to system design. Since site measurements are costly, propagation models have been developed as a suitable, low-cost, and convenient alternative. Channel modeling is required to predict path, loss and to characterize the impulse response of the propagating channel. The path loss is associated with the design of base stations, as this tells us how much a transmitter needs to radiate to service a given region. Channel characterization, on the other hand, deals with the fidelity of the received signals, and has to do with the nature of the waveform received at a receiver. The objective here is to design a suitable receiver that will receive the transmitted signal, distorted due to the multipath and dispersion effects of the channel, and that will decode the transmitted signal. An understanding of the various propagation models can actually address both problems. This paper begins with a review of the information available on the various propagation models for both indoor and outdoor environments. The existing models can be classified into two major classes: statistical models and site-specific models. The main characteristics of the radio channel - such as path loss, fading, and time-delay spread - are discussed. Currently, a third alternative, which includes many new numerical methods, is being introduced to propagation prediction. The advantages and disadvantages of some of these methods are summarized. In addition, an impulse-response characterization for the propagation path is also presented, including models for small-scale fading, Finally, it is shown that when two-way communication ports can be defined for a mobile system, it is possible to use reciprocity to focus the energy along the direction of an intended user without any explicit knowledge of the electromagnetic environment in which the system is operating, or knowledge of the spatial locations of the transmitter and the receiver.

898 citations

Journal ArticleDOI
TL;DR: This paper provides an overview of the existing multibeam antenna technologies which include the passiveMultibeam antennas (MBAs) based on quasi-optical components and beamforming circuits, multibeams phased-array antennas enabled by various phase-shifting methods, and digital MBAs with different system architectures.
Abstract: With the demanding system requirements for the fifth-generation (5G) wireless communications and the severe spectrum shortage at conventional cellular frequencies, multibeam antenna systems operating in the millimeter-wave frequency bands have attracted a lot of research interest and have been actively investigated. They represent the key antenna technology for supporting a high data transmission rate, an improved signal-to-interference-plus-noise ratio, an increased spectral and energy efficiency, and versatile beam shaping, thereby holding a great promise in serving as the critical infrastructure for enabling beamforming and massive multiple-input multiple-output (MIMO) that boost the 5G. This paper provides an overview of the existing multibeam antenna technologies which include the passive multibeam antennas (MBAs) based on quasi-optical components and beamforming circuits, multibeam phased-array antennas enabled by various phase-shifting methods, and digital MBAs with different system architectures. Specifically, their principles of operation, design, and implementation, as well as a number of illustrative application examples are reviewed. Finally, the suitability of these MBAs for the future 5G massive MIMO wireless systems as well as the associated challenges is discussed.

737 citations

Patent
24 Oct 2007
TL;DR: In this paper, improved capabilities are described for a Radio Frequency ID (RFID) tag that contains multiple Radio Frequency (RF) network nodes that provide enhanced memory capabilities, redundant functionality, and multiple frequency capabilities to the RFID tag using an inter-RF network node communication connection.
Abstract: In embodiments of the present invention improved capabilities are described for a Radio Frequency ID (RFID) tag that contains multiple Radio Frequency (RF) network nodes that provide enhanced memory capabilities, redundant functionality, and multiple frequency capabilities to the RFID tag using an inter-RF network node communication connection. The inter-RF network node communication may allow the coordination of RFID tag memory and functionality.

289 citations

Patent
18 Feb 2003
TL;DR: In this article, a method and system for providing point of sale and point-of-delivery and/or distribution of products in a restricted access unit near the customer is presented.
Abstract: A method and system for providing point-of-sale and point-of-delivery and/or distribution of products in a restricted access unit near the customer. The method and system utilize products equipped with radio frequency tags and reduce the effects of energy sharing, shadowing, and nulls. In one embodiment, a plurality of RF tagged products are placed within a refrigerator, cabinet, or other micro-warehouse that has a door or opening that can detect access to the micro-warehouse. In one embodiment, one or more antennas are positioned within the door. Each antenna may have a transmission line of sight and be configured to emit a signal at predefined frequencies. Each antenna generates an electromagnetic field within the micro-warehouse. In one embodiment, the products are positioned in one or more bins, compartments, or similar devices located within the micro-warehouse such that at least two of the plurality of products are spaced a distance from each other to reduce energy sharing. The electromagnetic field is moved or altered within the micro-warehouse through the use of reflectors, devices that move the antennas, or other mechanisms.

278 citations

Patent
08 Jun 2012
TL;DR: In this paper, a dielectric antenna is divided into a first region and a second region, and the second region could have a bending portion, and a conductor covers a surface of the second regions of the unit to form a waveguide structure.
Abstract: A dielectric antenna includes at least one dielectric unit. Each dielectric unit is separated into a first region and a second region, and the second region could have a bending portion. A conductor covers a surface of the second region of the dielectric unit to form a waveguide structure. The waveguide structure has a first endpoint connected to the first region and a second endpoint serving as a signal feeding terminal for feeding or receiving signals.

264 citations