Yoonjae Lee

Low-Profile Directive Millimeter-Wave Antennas Using Free-Formed Three-Dimensional (3-D) Electromagnetic Bandgap Structures

We present design methodologies for directive millimeter-wave antennas using free-formed three-dimensional (3-D) electromagnetic bandgap (EBG) structures. Dispersion characteristics of 3-D EBGs have been computed by finite-difference time-domain (FDTD) simulations and the designed EBGs have been fabricated by using the extrusion free-forming technique. The fabricated EBG structures have been measured and integrated with a waveguide feed to form a Fabry-Perot cavity antenna. The prototype antenna demonstrated 10deg to 14deg beamwidths with measured gain of 13 dBi. The woodpile EBG antenna achieved a narrow beamwidth without resorting to complex arrays or bulky reflectors, which would make the antenna well-suited for millimeter-wave broadband mobile communications, imaging and space applications.

A compact microstrip antenna with improved bandwidth using Complementary Split-Ring Resonator (CSRR) loading

In this paper, we investigate a microstrip patch antenna on a dielectric substrate with CSRRs employed in the ground plane, and examine the resonant frequency, impedance bandwidth, and radiation characteristics. The comparison of the impedance bandwidth between the microstrip patch antenna on a conventional high permittivity substrate and with the CSRR substrate is presented. The experimental results demonstrated that significant size reduction is possible for a microstrip antenna without sacrificing the bandwidth by using the CSRR loaded ground plane. The fabricated antenna achieves a 69% reduction in the resonant frequency as well as 67% improvement in the bandwidth compared to the conventional antenna.

Design of a solid-state nanopore-based platform for single-molecule spectroscopy

We numerically assess the light propagation and distribution characteristics of electromagnetic fields on nanopores formed in dielectric and metal/dielectric membranes using a frequency-domain finite element method (3D full-wave electromagnetic field simulation). Results of such studies were used to identify aluminum as an ideal material for use in optically thick metal/dielectric membranes. The comparison between SiN and Al/SiN membranes (with and without a submicron sized aperture) was numerically and experimentally shown to verify the effect of optically thick metal layers on light propagation and fluorescence excitation. The cut-off behavior for Al/SiN membranes with varying pore diameters was investigated in terms of light propagation, distribution of electromagnetic fields, and light attenuation characteristics.

Investigation of electromagnetic bandgap (EBG) structures for antenna pattern control

In this paper we investigate the use of a variety of EBG structures as components of a number of different antenna designs, with a view to assessing their pattern control capabilities. The EBG configurations investigated include both the one- and two-dimensional geometries comprising of dielectric slabs and rods as well as air pockets in the dielectric. The antenna types used to investigate the EBG materials are microstrip patch, dielectric resonator (DRA) and tapered slot (TSA) types. We compare the numerical simulation results for the gain patterns of original antennas (no EBG) with those that have EBG materials. The studies show that it is not a trivial task to control the radiation characteristics of planar and three-dimensional antennas described in this paper by using EBG structures.

Electromagnetic interference mitigation by using a spread-spectrum approach

We investigate a new technique, referred to as spread-spectrum clock generation (SSCG), for reducing the level of radiated emission from devices with digital clock signals. To calculate the radiated emissions from such devices, we model the radiating geometry and compute the radiated field at a multitude of frequencies by using NEC-4, which is an electromagnetic field solver based on the method of moments (MoM). We consider a variety of modulating profiles for the spread spectrum clock and demonstrate that by using a frequency deviation of only 1%, we can achieve from 10 to 30 dB reduction in the radiated emission levels.

A novel modified Sierpinski patch antenna using shorting pins and switches for multiband applications

A two-layer configuration of the Sierpinski gasket patch antenna is investigated, and a new technique for improving the matching characteristics and the radiation pattern is proposed. We demonstrate that the original two-layer design does not exhibit the desired performance from the point of view of the matching and radiation pattern, and show how this can be modified to improve its performance.

Directive millimetrewave antennas using freeformed ceramic metamaterials in planar and cylindrical forms

In this paper, we presented applications of millimetrewave EBG structures fabricated using a rapid prototyping technique based on extrusion freeforming. Numerical simulations were performed for the design of millimetrewave woodpile structures. The fabricated woodpile structures have been measured and showed a good agreement with the simulated results. A directive millimetrewave antenna utilising freeformed EBG superstrate with tapered reflectance has been demonstrated. The new EBG superstrate achieves reduced side lobes by reducing the reflection from the edges. We have fabricated for the first time the cylindrical EBG structures and designed a directive fanbeam antenna for high data rate indoor wireless applications at millimetrewave frequencies. The extrusion freeforming is a flexible and versatile technique for realising various non-homogeneous 3D bandgap structures with arbitrary geometries at millimetrewave bands.

Fractal and multiband communication antennas

In this paper we present two novel multiband antenna designs for multiple frequency applications. The first of these, which is based on fractal concepts, is a Sierpinski gasket type of fractal configuration, printed on a dielectric substrate backed by a ground plane. We propose a novel approach to enhancing its multiband performance, in terms of impedance matching characteristics as well as radiation patterns, at three operating frequencies. The second design combines a rectangular microstrip patch with a cylindrical dielectric resonator, and operates at multiple frequencies. Specifically, we describe a stacked configuration of a dielectric resonator antenna on a microstrip patch for three frequency bands. Circular polarization is obtained by utilizing four coaxial feeds in phase quadrature. This configuration is found to exhibit good cross-polarisation rejection characteristics.

Multi-band L/sub 5/-capable GPS antenna with reduced backlobes

We present a novel multiband antenna design for GPS applications at three different frequencies (L/sub 1/-1575.42MHz, L/sub 2/-1227.60MHz, and L/sub 5/-1176.45MHz). The future GPS system will introduces an L/sub 5/ capability, allowing the possibility of extended services using the new GPS signal. The designed antenna employs the aperture-coupled stacked patch configuration and achieves improved performance in terms of bandwidths, axial ratios, cross-polarization rejection levels and multipath rejection characteristics. To mitigate the multipath interference, a novel structure (vertical choke ring) using multiple metallic disks with center cylinders of different diameters was introduced. The use of the vertical choke ring helps achieve very low backlobes, without the need to increase the diameter of the ground plane, by suppressing the surface waves and the edge diffractions. The designed antenna has been fabricated and tested. The measured performance of the designed antenna is presented in the paper.

Extrusion freeforming of millimeter wave electromagnetic bandgap (EBG) structures

Purpose – The aim of this paper is to provide an easy method of extrusion freeforming to fabricate microwave electromagnetic bandgap (EBG) crystals. EBG crystals are periodic dielectric structures that can block wave propagation and generate a bandgap. These crystals can be used in high capability antennae, electromagnetic wave semiconductors, microresonators, high‐reflectivity mirrors and polarizing beam splitters.Design/methodology/approach – The effects of extrusion process parameters and paste characteristics were investigated. Finally, one‐period and two‐period woodpile EBG crystals with bandgaps in the frequency region of 90‐110 GHz were fabricated and the bandgap was measured.Findings – The filament diameter is influenced by whether extrusion is carried out with or without a substrate and by the free fall‐distance from the nozzle. The quality of lattice structures is dependent on paste flow and properties. A ceramic paste with 60 vol. % (the fraction of ceramic powder based on solvent‐free polymer)...