Kyungho Yoo

A novel technique for enhancing the directivity of microstrip patch antennas using an EBG superstrate

This paper presents a novel and systematic approach for enhancing the directivity of an antenna/EBG composite, comprising of a microstrip patch antenna covered by an FSS superstrate. The method is based on the initial simulation of the composite operating in the receive mode, mapping the field distribution in the Fabry-Perot type cavity region formed by the superstrate and the ground plane. Additionally, we correlate the results for the frequency response of an associated two-layer structure - formed by the superstrate and its image through the ground plane - by using the Finite Difference Time Domain (FDTD) method. Furthermore, the field distributions inside the cavity for oblique incidence are investigated, again when operating in the receive mode, to relate the angular response with the antenna pattern.

Modeling and Design of Wideband Antennas For Body Area Networks (BANs)

Recently, there has a growing interest in the development and implementation of body area networks. These systems are intended to operate in a similar fashion to wireless land area networks (WLAN) with exception that they are strictly confined to the human body. This type of technology has risen in demand due to the growing abundance of portable computing devices. However, the human body creates a challenging environment for the design of wearable antennas that can communicate efficiently. As a result, a detailed study of the on body communication channel is required. Lastly, many of these systems are intended to operate over a very wide frequency band. Therefore, the design of ultra wide band antennas (UWB) is a pertinent area of research in this technology

Directivity enhancement of microstrip antennas using dielectric superstrates

The subject of directivity enhancement of microstrip patch antennas (MPAs), using either a Frequency Selective Surface (FSS) or a double-negative (DNG) metamaterial slab, has been investigated by a number of researchers in recent years. The purpose of this paper is to show that we can also achieve the same goal by using a much simpler design for the superstrate, namely a dielectric slab, whose performance can comparable, and even be superior to those of the other two typical choices for the superstrate, namely the FSS or the DNG.

Realization of high directivity enhancement by using an array of microstrip patch antennas (MPAs) covered by a dielectric superstrate

In this paper we present a Fabry-Perot type of design, involving a microstrip array covered by a 14λ0χ14λ0 superstrate that realizes a directivity of 32 dB when excited by an array of 25 microstrip patches. We show that the directivity of the array can be enhanced by an additional 2 dB by using a two-layer superstrate. We present the radiation patterns for the two cases to show that the sidelobe level for the two-layer case is lower than that for the one-layer version. We also carry out a parametric study of the superstrates layers and the distance between the lower superstrate and the ground plane, and examine how the separation distance between the two superstrate layers affects the resonant frequency of the composite structure.

A new technique for the simulation of periodic structures including EBGs and Metamaterials

Because the EBGs [1] and Metamaterial structures that exhibit interesting characteristics are almost always strictly periodic in nature and because there is an increasing interest in synthesizing new versions of these structures, we need access to both techniques-and computer codes developed on the basis of these techniques-to accomplish our own design goals. Some of the design objectives of Metamaterials are: (i) achieving close to isotropic scattering characteristics from an MTM slab; (ii) obtaining wider bandwidths and less dispersive behaviors; (iii) realizing low-loss characteristics; (iv) reducing the dependence on incident angle and polarization of the incident wave.

Modeling of interaction between body-mounted antennas

As wearable electronic devices continue to become popularized, there is an increasing demand for these components to provide the capability of exchanging data wireless with high capacity. Currently, there is strong motivation for the development of body-centric link networks. The efficiency of these networks relies heavily on the propagation characteristics of radiated energy in the presence of the user. To properly design such systems, a careful study of this behavior and the appropriate choice of the antenna are necessary. In this paper, the authors have addressed both the coupling of antennas mounted on the body and the design of ultra-wide-band antennas (UWB) which meet the required capacity of such systems.

A novel technique for the analysis of periodic structures including EBGs

It has been demonstrated in recent years that the directivity of planar antennas can be enhanced by using Electromagnetic Bandgap (EBG) structures, e.g., Frequency Selective Surfaces (FSS) as superstrates [1–2]. However, the modeling of these structures can be computationally intensive, and may demand large memory resources especially when simulating FSSs whose elements have fine features. It is therefore important to develop EM simulation techniques that reduce the run-times sufficiently, so as to make them more suitable as design tools than are the existing codes. In this paper, we describe a new technique for modeling periodic structures that is both memory- and time-efficient. Although the method is quite general, we choose, for the sake of illustration, FSS elements comprising of wire tripoles, as shown in Fig.1. Some of the existing FSS codes, including commercial ones often have difficulties in dealing with this type of geometry, especially when the wire diameter is small. In fact, some codes are even unable to handle the geometries and are forced to model them only as strips. The present method can not only model either the strip or the wire structure, but also the case when the tripole element has an arbitrary orientation, and the FSS is no longer planar. One of the strong points of the proposed method is that it reduces the matrix size to only 2 or 3, by utilizing a combination of newly developed Dipole Moment (DM) and the Characteristic Basis Function Method (CBFM) [3]. The matrix equation is first constructed for the isolated element in order to extract the Characteristic Basis Functions (CBFs). The matrix is then generalized for the truncated periodic case, without using additional unknowns. Finally, the solution for the truncated structure is processed by using Pronys method to extrapolate the solution for the current distribution for the infinite doubly-periodic case. The last step is to utilize the extrapolated solution to compute the reflection coefficient for the infinite array problem by using the Reciprocity Principle. As mentioned earlier, the techniques presented herein for the solution of the induced current, as well as for the computation of the reflection coefficient are very general, and are applicable to arbitrary geometries that can in general be three-dimensional in nature. Before closing this section, we mention that unlike the conventional Method of Moments (MoM), the present formulation utilizes closed-form expressions to compute the fields radiated by the CBFs, and no Greens functions are used — either periodic- or free-space-types — to generate the MoM-matrix elements [4].

Advanced impedance matching technology to optimize RF circuit design of practical wireless systems

In this paper, the novel impedance matching method using multiport network analysis and the particle swarm optimization (PSO) algorithm is proposed. To evaluate the accuracy and reliability of the proposed method, the real handset model is employed, and the target impedance matching is conducted. Good impedance matching results are obtained in the long term evolution (LTE) band8. The calculated results are in excellent agreement with target impedance, under the relative voltage standing wave ratio (RVSWR) of 1.5. Compared with the reference model, measured output power (Pout), adjacent current power ratio (ACPR), and current consumption of the power-amp module (/pam) have errors within 0.5dBm, 3dBc, and 35mA, respectively. The proposed method can offer practical solutions for real RF matching problems to engineers in the beginning step of PCB design.

A numerically efficient approach to metamaterial (MTM) modeling

Ever since the existence of negative refraction by metamaterial prisms was demonstrated by Pendry, Smith and others about a decade ago, the subject has received a tremendous amount of attention from many researchers around the world. A special class of MTMs, namely double negative or DNG type of artificially synthesized materials, has been used not only to design superlenses, but to also enhance the directivity of antennas, such as microstrip patch antennas (MPAs) [1–2]. In the process, the terms MTMs and DNGs have become almost synonymous; it is not uncommon to find them being used interchangeably with one another in the literature.

A new technique for the numerical simulation of periodic structures including EBGs, FSSs and Metamaterials

This paper describes a newly developed dipole moment (DM) approach, for modeling periodic structures. It is both memory- and time-efficient, and is applicable to arbitrarily shaped elements, whose material properties can also be arbitrary.