Wee Sang Park

Bio: Wee Sang Park is an academic researcher from Pohang University of Science and Technology. The author has contributed to research in topics: Antenna (radio) & Microstrip antenna. The author has an hindex of 20, co-authored 139 publications receiving 1589 citations. Previous affiliations of Wee Sang Park include University of Wisconsin-Madison & 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.

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

A Novel Design Technique for Control of Defect Frequencies of an Electromagnetic Bandgap (EBG) Superstrate for Dual-Band Directivity Enhancement

Abstract: In this paper, we propose a novel design technique to control the defect frequencies of an electromagnetic bandgap (EBG) superstrate with the objective of enhancing the directivity of a patch antenna at two frequencies. Two different defect configurations, the first of which is introduced by the ground plane of the antenna while the other is produced by a row of rods with dissimilar dielectric constants in the EBG structure, are examined in detail in order to achieve dual-band operation. We begin by investigating the EBG structure and varying several of its parameters to determine the locations of the bandgap and defect frequencies, as well as their controllability. Finally, the promising designs for the EBG superstrates, which provide enhanced directivities for the EBG antenna, are evaluated to validate the proposed design scheme. It is demonstrated that the directivity of the antenna with a 12 × 3 EBG superstrate increases to 18 and 18.5 dBi, respectively, at the two design frequency bands, as compared to that of the antenna alone (maximum 10 dBi) without the superstrate. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 25–31, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20196

A 3-position transmission/reflection method for measuring the permittivity of low loss materials

Abstract: A 3-position transmission/reflection method for measuring the permittivity of low loss materials is presented. In this method, the measurement errors of the permittivity due to (1) the mismatch at the connections, (2) the metallic loss of the holder, (3) the uncertainty of sample position in the airline, and (4) the imperfection of the calibration kit can be removed by the measured data for a sample at three different positions. Experimental results for a low loss engineering plastic (tan /spl delta//spl cong/0.025) are included. >

A 3-Position TransmissiodReflection Method for Measuring the Permittivity of Low Loss Materials

Abstract: A 3-position transmission/reflection method for measuring the permittivity of low loss materials is presented. In this method, the measurement errors of the permittivity due to (1) the mismatch at the connections, (2) the metallic loss of the holder, (3) the uncertainty of sample position in the airline, and (4) the imperfection of the calibration kit can be removed by the measured data for a sample at three different positions. Experimental results for a low loss engineering plastic (tan /spl delta//spl cong/0.025) are included. >

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

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.

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

Abstract: Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

Dual-band reconfigurable antenna with a very wide tunability range

Abstract: A new technique for designing dual-band reconfigurable slot antennas is presented. Dual-frequency operation is achieved by loading a slot antenna with two lumped variable capacitors (varactors) placed in proper locations along the slot. Loading the slot antenna with lumped capacitors shifts down the resonant frequencies of the first and second resonances of the antenna. However, these frequency shifts depend not only on the values of the capacitors, but also on their locations along the slot antenna. Here, it is shown that by choosing the locations of the varactors appropriately, it is possible to obtain a dual-band antenna whose first and second resonant frequencies can be controlled individually. In other words, the frequency of either the first or the second band can be fixed, while the other one is electronically tuned. Using such a design, an electronically tunable dual-band antenna is designed and fabricated using two identical varactors having a capacitance range of 0.5-2.25 pF. The antenna is shown to have a frequency ratio (f/sub R/=f/sub 2//f/sub 1/) ranging from 1.3 to 2.67. An important feature of this antenna is its consistent radiation pattern, polarization, and polarization purity at both bands and across its entire tunable frequency range.