Junho Yeo

Bio: Junho Yeo is an academic researcher from Daegu University. The author has contributed to research in topics: Antenna (radio) & Microstrip antenna. The author has an hindex of 24, co-authored 147 publications receiving 2175 citations. Previous affiliations of Junho Yeo include Pennsylvania State University & Electronics and Telecommunications Research Institute.

Application of electromagnetic bandgap (EBG) superstrates with controllable defects for a class of patch antennas as spatial angular filters

Abstract: We present some applications of an electromagnetic bandgap (EBG) superstrate as a spatial angular filter for filtering undesired radiation by sharpening the radiation pattern. Two different defects, one introduced by the ground plane of the antenna and the other produced by a row of defect rods with different dielectric constants in the EBG structure, are simultaneously used as key controllers of directivity enhancement. Initially, we study the unit cell of the EBG structures by varying several parameters, in order to understand how they influence the locations of the bandgap and defect frequencies. Next, the defect frequencies of the unit cell of the EBG cover, and those with high directivity for the EBG antenna composite, are compared to validate the proposed design scheme. Finally, we introduce some interesting applications of EBG superstrates for various types of patch antennas as spatial angular filters, such as a dual-band orthogonally-polarized antenna, a wide-band directive antenna, and an array antenna with grating lobes.

Efficient analysis of a class of microstrip antennas using the characteristic basis function method (CBFM)

Abstract: This paper presents a novel approach for the efficient solution of a class of microstrip antennas using the newly introduced characteristic basis functions (CBFs) in conjunction with the method of moments (MoM). The CBFs are special types of high-level basis functions, defined over domains that encompass a relatively large number of conventional subdomain basis functions, for example, triangular patches or rooftops. The advantages of applying the CBF method (CBFM) are illustrated by several representative examples, and the accuracy as well as the computation time are compared to those of conventional direct computation. It is demonstrated that the use of CBFs can result in significant savings in computation time, with little or no compromise in the accuracy of the solution. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 456–464, 2003

Design of a high-directivity Electromagnetic Band Gap (EBG) resonator antenna using a frequency-selective surface (FSS) superstrate

Abstract: In this paper, we introduce a novel design for a high-directivity Electromagnetic Band Gap (EBG) resonator antenna that utilizes a frequency-selective surface (FSS) superstrate. The above type of superstrate is proposed as an alternative to an EBG type of dielectric superstrate—investigated previously by the authors—to reduce its height and facilitate the fabrication process. Although FSS superstrate and the patch antenna comprise a composite resonator, we begin by investigating the FSS structure characteristics first before dealing with the combination. We vary several important parameters, such as the distance between the FSS superstrate and the ground plane of the antenna, and the dimensions of the FSS superstrate, to determine their effect on the resonant frequency and the quality factor of the unit cell of the FSS. The above study enables us to derive some guidelines for an optimum array size of the FSS superstrate that eventually leads to a maximum directivity for the FSS antenna composite, as evidenced via a comparison of the quality factors of the FSS, the unit cell, and the composite. It is demonstrated that the directivity of the antenna with an optimized array size of the FSS superstrate increases by 17.29 to 24.92 dBi for three different strip-dipole lengths, as compared to that of the patch antenna alone (maximum 6 dBi). © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 462–467, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20502

Dual-Band Long-Range Passive RFID Tag Antenna Using an AMC Ground Plane

Abstract: A dual-band passive radio frequency identification (RFID) tag antenna applicable for a recessed cavity in metallic objects such as heavy equipment, vehicles, aircraft, and containers with long read range is proposed by using an artificial magnetic conductor (AMC) ground plane. The proposed tag antenna consists of a bowtie antenna and a recessed cavity with the AMC ground plane installed on the bottom side of the cavity. The AMC ground plane is utilized to provide dual-band operation at European (869.5 869.7 MHz) and Korean (910 914 MHz) passive UHF RFID bands by replacing the bottom side of the metallic cavity of a PEC-like behavior and, therefore, changing the reflection phase of the ground plane. It is worthwhile to mention that the European and the Korean UHF RFID bands are allocated very closely, and the frequency separation ratio between the two bands is just about 0.045, which is very small. It is demonstrated by experiment that the maximum reading distance of the proposed tag antenna with optimized dimensions can be improved more than 3.1 times at the two RFID bands compared to a commercial RFID tag.

Design of novel thin frequency selective surface superstrates for dual-band directivity enhancement

Abstract: A novel design for a thin frequency selective surface (FSS) type of metamaterial superstrate for dual-band directivity enhancement is presented as an alternative to a conventional FSS superstrate which is thicker. In the proposed new design, two strip-dipole arrays with the same periodicity, but with different alignments are placed above and below a thin dielectric layer to overcome the problem of different directivities realised at the two bands, when two FSS arrays with dissimilar periodicities are used. On the basis of unit-cell simulation, several important parameters that characterise the thin FSS superstrate are investigated, and the procedure for designing such a superstrate is described. Resonant frequencies and quality factors of the unit cell are compared with those of three FSS antenna composites with different quality factors and the optimal quality factors for the dual-band directivity enhancement are identified. Additionally, how to choose the optimal FSS array size for which the superstrate enhances directivity most efficiently is discussed. An antenna composite has been fabricated to validate the proposed approach, and the measured results show good agreement with the simulated ones.

An overview of fractal antenna engineering research

Abstract: Recent efforts by several researchers around the world to combine fractal geometry with electromagnetic theory have led to a plethora of new and innovative antenna designs. In this report, we provide a comprehensive overview of recent developments in the rapidly growing field of fractal antenna engineering. Fractal antenna engineering research has been primarily focused in two areas: the first deals with the analysis and design of fractal antenna elements, and the second concerns the application of fractal concepts to the design of antenna arrays. Fractals have no characteristic size, and are generally composed of many copies of themselves at different scales. These unique properties of fractals have been exploited in order to develop a new class of antenna-element designs that are multi-band and/or compact in size. On the other hand, fractal arrays are a subset of thinned arrays, and have been shown to possess several highly desirable properties, including multi-band performance, low sidelobe levels, and the ability to develop rapid beamforming algorithms based on the recursive nature of fractals. Fractal elements and arrays are also ideal candidates for use in reconfigurable systems. Finally, we provide a brief summary of recent work in the related area of fractal frequency-selective surfaces.

The art of UHF RFID antenna design: impedance-matching and size-reduction techniques

Abstract: Radio-frequency identification technology, based on the reader/tag paradigm, is quickly permeating several aspects of everyday life. The electromagnetic research mainly concerns the design of tag antennas having high efficiency and small size, and suited to complex impedance matching to the embedded electronics. Starting from the available but fragmented open literature, this paper presents a homogeneous survey of relevant methodologies for the design of UHF passive tag antennas. Particular care is taken to illustrate, within a common framework, the basic concepts of the most-used design layouts. The design techniques are illustrated by means of many noncommercial examples.

Antenna miniaturization and bandwidth enhancement using a reactive impedance substrate

Abstract: The concept of a novel reactive impedance surface (RIS) as a substrate for planar antennas, that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna is introduced. Using the exact image formulation for the fields of elementary sources above impedance surfaces, it is shown that a purely reactive impedance plane with a specific surface reactance can minimize the interaction between the elementary source and its image in the RIS substrate. An RIS can be tuned anywhere between perfectly electric and magnetic conductor (PEC and PMC) surfaces offering a property to achieve the optimal bandwidth and miniaturization factor. It is demonstrated that RIS can provide performance superior to PMC when used as substrate for antennas. The RIS substrate is designed utilizing two-dimensional periodic printed metallic patches on a metal-backed high dielectric material. A simplified circuit model describing the physical phenomenon of the periodic surface is developed for simple analysis and design of the RIS substrate. Also a finite-difference time-domain (FDTD) full-wave analysis in conjunction with periodic boundary conditions and perfectly matched layer walls is applied to provide comprehensive study and analysis of complex antennas on such substrates. Examples of different planar antennas including dipole and patch antennas on RIS are considered, and their characteristics are compared with those obtained from the same antennas over PEC and PMC. The simulations compare very well with measured results obtained from a prototype /spl lambda//10 miniaturized patch antenna fabricated on an RIS substrate. This antenna shows measured relative bandwidth, gain, and radiation efficiency of BW=6.7, G=4.5 dBi, and e/sub r/=90, respectively, which constitutes the highest bandwidth, gain, and efficiency for such a small size thin planar antenna.

Electromagnetic Band Gap Structures in Antenna Engineering

Abstract: Preface 1. Introduction 2. FDTD Method for periodic structure analysis 3. EBG Characterizations and classifications 4. Design and optimizations of EBG structures 5. Patch antennas with EBG structures 6. Low profile wire antennas on EBG surfaces 7. Surface wave antennas Appendix: EBG literature review.