Showing papers by "Hossein Mosallaei published in 2004"
TL;DR: In this article, the authors proposed a 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.
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.
653 citations
TL;DR: In this paper, a woodpile EBG made up of magneto-dielectric material is proposed for the design of novel EM structures with applications in the VHF-UHF bands.
Abstract: In this paper, the unique features of periodic magneto-dielectric meta-materials in electromagnetics are addressed. These materials, which are arranged in periodic configurations, are applied for the design of novel EM structures with applications in the VHF-UHF bands. The utility of these materials is demonstrated by considering two challenging problems, namely, design of miniaturized electromagnetic band-gap (EBG) structures and antennas in the VHF-UHF bands. A woodpile EBG made up of magneto-dielectric material is proposed. It is shown that the magneto-dielectric woodpile not only exhibits band-gap rejection values much higher than the ordinary dielectric woodpile, but also for the same physical dimensions it shows a rejection band at a much lower frequency. The higher rejection is a result of higher effective impedance contrasts between consecutive layers of the magneto-dielectric woodpile structure. Composite magneto-dielectrics are also shown to provide certain advantages when used as substrates for planar antennas. These substrates are used to miniaturize antennas while maintaining a relatively high bandwidth and efficiency. An artificial anisotropic meta-substrate having /spl mu//sub r/>/spl epsiv//sub r/, made up of layered magneto-dielectric and dielectric materials is designed to maximize the bandwidth of a miniaturized patch antenna. Analytical and numerical approaches, based on the anisotropic effective medium theory (AEMT) and the finite-difference time-domain (FDTD) technique, are applied to carry out the analyzes and fully characterize the performance of finite and infinite periodic magneto-dielectric meta-materials integrated into the EBG and antenna designs.
473 citations
01 Jan 2004
TL;DR: In this article, it has been shown that the zero-order bandwidth for an antenna over a magneto-dielectric substrate with thickness t can be approximated by the characteristic impedance of the surrounding medium (r r e µ η η 0 = ).
Abstract: ( r n e µ = ). Therefore, the issue of strong field confinement is minimized and the medium is far less capacitive when compared to the dielectric-only high permittivity material. Furthermore, since the characteristic impedance of magneto-dielectric medium ( r r e µ η η 0 = ) is close to that of the surrounding medium ( 0 η ) it allows for ease of impedance matching over a much wider bandwidth. It has been shown by Hansen and Burke [2], that the zero-order bandwidth for an antenna over a magneto-dielectric substrate with thickness t can be approximated by
29 citations
20 Jun 2004
TL;DR: In this article, the magnetic metamaterial exhibited enhanced /spl mu/ and /spl epsiv/ as predicted with acceptable loss-factor levels, and simulations indicate that magnetic permeability can be extended well beyond several GHz with current technology.
Abstract: Magnetic permeability was imparted to a naturally non-magnetic material by metallic inclusions. A patch antenna tested the performance of the magnetic metamaterial as a substrate. The magnetic metamaterial exhibited enhanced /spl mu/ and /spl epsiv/ as predicted with acceptable loss-factor levels. Models for predicting /spl mu/ and /spl epsiv/ are presented and simulations indicate that permeability can be extended well beyond several GHz with current technology. Permeability in the /spl mu//sub r/=1-4 range is achievable for moderately low-loss applications. The representative antenna miniaturization factor=4-6.4 with efficiency=21-35%.
24 citations
20 Jun 2004
TL;DR: In this article, the authors presented the application of embedded-circuit meta-material (ECM) and reactive impedance surface (RIS) substrates for novel antenna designs, and proposed a novel compact RIS as the ground plane for a dual-band E-shaped patch/slot antennna to reduce the interaction of the antenna with its ground and design a miniaturized wideband antenna system.
Abstract: Antenna miniaturization with enhanced radiation performance is a contemporary problem with application in RF and wireless systems. The substrate and ground plane of the antenna play a very important role in achieving the desired antenna characteristics. The focus in this paper is to present the application of two types of meta-substrates for novel antenna designs, namely, embedded-circuit meta-material (ECM) and reactive impedance surface (RIS) substrates. ECM provides a way to fabricate an /spl epsiv/-/spl mu/ substrate, and allows antenna miniaturization with relatively high bandwidth and efficiency. Also, a novel compact RIS as the ground plane for a dual-band E-shaped patch/slot antennna is proposed, to reduce th interaction of the antenna with its ground and design a miniaturized wideband antenna system.
9 citations
20 Jun 2004
TL;DR: It is demonstrated that a GA-optimized SCA can provide a wide bandwidth ratio of about 1:5 which occupies an area as small as /spl Lambda//4/spl times//spl lambda//4 at the lowest frequency.
Abstract: The focus in this paper is to design a compact ultra-wideband self-complementary antenna (SCA) optimized for bandwidth constrained by size. The concept of frequency independent self-complementary geometries is applied to achieve the highest bandwidth possible, and a genetic algorithm (GA) optimization method is used to provide the optimal planar antenna topology and substrate design in an available finite space. An FDTD technique is used to fully analyze the complex antenna structures. It is demonstrated that a GA-optimized SCA can provide a wide bandwidth ratio of about 1:5 which occupies an area as small as /spl lambda//4/spl times//spl lambda//4 at the lowest frequency. An equally spaced alternate-leaves SCA on an optimized meta-substrate is also proposed that provides ultra-wideband bandwidth characteristics (bandwidth ratio 1:8) with as small dimensions as /spl lambda//3/spl times//spl lambda//3.
6 citations
20 Jun 2004
TL;DR: In this article, a dual-resonance characteristic is achieved by merging the resonances of an aperture antenna and a DRA; miniaturization is provided by the high dielectric constant of the resonator.
Abstract: The paper presents the concept and implementation of a wideband, high-gain miniaturized dielectric resonator antenna (DRA). A dual-resonance characteristic is achieved by merging the resonances of an aperture antenna and a DRA; miniaturization is provided by the high dielectric constant of the resonator. The design enhances the bandwidth of the constituent antennas without compromising their efficiency and radiation characteristics. In addition, the design enforces low cross-polarization levels as well its a unique polarization direction over the entire bandwidth. It is shown that, with proper design, the two resonances inherent in all DRA designs with resonant feed structures can be merged for bandwidth optimization. In addition, the similarity of the aperture and DRA radiation characteristics allows preservation of the radiation patterns and polarization over the entire bandwidth. The design parameters are summarized and simulation results given. A 0.2/spl lambda//sub 0/ antenna exhibiting over 25% bandwidth and gain exceeding 4 dBi has been built and characterized.
6 citations