Study of Antenna Superstrates Using Metamaterials for Directivity Enhancement Based on Fabry-Perot Resonant Cavity

Metamaterial superstrate is a significant method to obtain high directivity of one or a few antennas. In this paper, the characteristics of directivity enhancement using different metamaterial structures as antenna superstrates, such as electromagnetic bandgap (EBG) structures, frequency selective surface (FSS), and left-handed material (LHM), are unifiedly studied by applying the theory of Fabry-Perot (F-P) resonant cavity. Focusing on the analysis of reflection phase and magnitude of superstrates in presently proposed designs, the essential reason for high-directivity antenna with different superstrates can be revealed in terms of the F-P resonant theory. Furthermore, a new design of the optimum reflection coefficient of superstrates for the maximum antenna directivity is proposed and validated. The optimum location of the LHM superstrate which is based on a refractive lens model can be determined by the F-P resonant distance

Modeling and Analysis of Composite Antenna Superstrates Consisting on Grids of Loaded Wires

We study the characteristics and radiation mechanism of antenna superstrates based on closely located periodical grids of loaded wires. An explicit analytical method based on the local field approach is used to study the reflection and transmission properties of such superstrates. It is shown that as a result of proper impedance loading there exists a rather wide frequency band over which currents induced to the grids cancel each other, leading to a wide transmission maximum. In this regime radiation is produced by the magnetic dipole moments created by circulating out-of-phase currents flowing in the grids. An impedance matrix representation is derived for the superstrates, and the analytical results are validated using full-wave simulations. As a practical application example we study numerically the radiation characteristics of dipole antennas illuminating finite-size superstrates.Comment: 9 pages, 11 figures. In the second version we have clarified the analysis related to the prototype, and re-desinged the prototype antenn

Resonant meta-surface superstrate for single and multifrequency dipole antenna arrays

The design of a multifrequency dipole antenna array based on a resonant meta-surface superstrate is proposed. The behavior of a single element that is closely placed to a meta-surface is experimentally investigated. The proposed meta-surface is based on resonating unit cells formed by capacitively loaded strips and split ring resonators. By tuning a dipole antenna to the pass band of the meta-surface, the physical area is effectively illuminated enhancing the radiation performance. The gain, radiation efficiency and effective area values of the whole configuration are compared to the ones obtained with a single dipole without superstrate. Radiation efficiency values for the proposed configuration of more than 80% and gain values of more than 4.5 1 dB are obtained. Based on this configuration, simulated results of a multifrequency antenna array are presented. Distinctive features of this configuration are high isolation between elements (20 dB for a distance of lambda0/4), and low back radiation

Design and Optimization of Electromagnetic Band Gap Structures

Dizertační práce pojednává o návrhu a optimalizaci periodických struktur s elektromagnetickým zádržným pásmem (EBG – electromagnetic band gap) pro potlačení povrchových vln šířících se na elektricky tlustých dielektrických substrátech. Nepředvídatelné chování elektromagnetických vlastností těchto struktur v závislosti na parametrech elementární buňky činí jejích syntézi značně komplikovanou. Bez patřičného postupu je návrh EBG struktur metodou pokusu a omylu. V první části práce jsou shrnuty základní poznatky o šíření elektromagnetických vln v tzv. metamateriálech. Následně je diskutován správný způsob výpočtu disperzního diagramu ve vybraných komerčních programech. Jádrem dizertace je automatizovaný návrh a optimalizace EBG struktur využitím různých globálních optimalizačních algoritmů. Praktický význam vypracované metodiky je předveden na návrhových příkladech periodických struktur s redukovanými rozměry, dvoupásmovými EBG vlastnostmi, simultánním EBG a AMC (artificial magnetic conductor – umělý magnetický vodič) chováním a tzv. superstrátu. Poslední kapitola je věnována experimentálnímu ověření počítačových modelů.The thesis deals with the design and optimization of periodic structures for surface waves suppression on electrically dense dielectric substrates. The design of such structures is rather complicated due to the large factor of uncertainty how the electromagnetic band gap (EBG) properties change depending on the unit cell geometry. Without a proper approach, the design of EBGs is based on trial-and-error. In this thesis, the basic theory of electromagnetic wave propagation in metamaterials is presented first. Second, the correct dispersion diagram computation in the selected full-wave software tools is discussed. The main attention is turned then to the automated design and optimization of EBG structures using different global evolutionary algorithms. The practical exploitation of the developed technique is demonstrated on design examples of reduced-size and dual-band EBGs, periodic structures with simultaneous electromagnetic band gap and artificial magnetic conductor (AMC) properties and periodic structures acting as superstrates. The last chapter of the thesis is devoted to the experimental verification of computer models.

Low-profile Circularly Polarized Antenna Exploiting Fabry-Perot Resonator Principle

We designed a patch antenna surrounded by a mushroom-like electromagnetic band-gap (EBG) structure and completed it by a partially reflective surface (PRS). EBG suppresses surface waves and creates the bottom wall of the Fabry-Perot (FP) resonator. PRS plays the role of a planar lens and forms the top wall of the FP resonator. The novel PRS consists of a two-layer grid exhibiting inductive and capacitive (LC) behavior which allows us to obtain a reflection phase between –108 and +180 degrees. Thanks to this PRS, we can control the height of the cavity in the range from λ/2 to λ/300. Obtained results show that the FP resonator antenna enables us to achieve a low profile and a high-gain. The patch is excited by a microstrip transmission line via the cross-slot aperture generating the circular polarization. Functionality of the described concept of the FP antenna was verified at 10 GHz. The antenna gain was 15 dBi, the impedance bandwidth 2.3% for |S11| < –10 dB, and the axial ratio bandwidth 0.6% for AR < 3.0 dB. Hence, the antenna is suitable for narrowband applications. Computer simulations show that the microwave FP antenna can be simply redesigned to serve as a source of circularly polarized terahertz waves

(Sub)millimeter-Wave Antennas

Disertační práce se zabývá návrhem a optimalizací kruhově polarizované anténa pro oblast terahertzových kmitočtů. V práci se věnuji zjednodušené teorii terahertzového zdroje a návrhu vhodné antény pro tento zdroj. Návrh je zaměřen na dosažení kruhové polarizace z lineárně polarizovaných antén. Abych potlačil šíření povrchové vlny na elektricky tlustém dielektrickém substrátu, věnuji se návrhu a optimalizaci specifických periodických struktur. Návrh těchto struktur je poměrně komplikovaný, protože neexistuje přímočarý vztah mezi vlastnostmi struktur s elektromagnetickým zádržným pásmem (EBG) a geometrií buňky. Abych vhodně koncentroval vyzařovanou energii do úzkého svazku, věnuji se návrhu a optimalizaci částečně odrazného plochy (PRS), které působí jako planární čočka pro terahertzovou anténu.The thesis deals with the design and optimization of circularly polarized antennas for THz frequencies. In the thesis, a simplified theory of THz sources is presented, and a suitable antenna for a THz source is designed. The design is focused on achieving circular polarization from linearly polarized antennas. In order to suppress surface waves on an electrically dense dielectric substrate, we design and optimize specific periodic structures. The design of such a structure is rather complicated since the relation between electromagnetic band gap (EBG) properties and unit cell geometry is not straightforward. In order to properly focus the radiated energy, we design and optimize a partially reflective surface (PRS) acting as a planar lens for the THz antenna.

2009 Index IEEE Antennas and Wireless Propagation Letters Vol. 8

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index

Biodegradable dual semicircular patch antenna tile for smart floors

A dual semicircular microstrip patch antenna implemented on a biodegradable substrate is presented for operation in the [863-873] MHz and [2.4-2.5] GHz frequency bands. To cover these frequency bands, two semicircular patches are compactly integrated onto a biodegradable cork tile, commonly found as support in laminate flooring, serving as a substrate. Thereby, the antenna tile may be seamlessly embedded as a sublayer of the floor structure. A higher-order mode is generated by applying via pins in the antenna topology to produce a conical radiation pattern with a null at broadside and sectoral coverage in the vertical plane. As such, the concealed floor antenna covers all azimuth angles of arrival in smart houses. The antenna performance is fully validated, also when the tile is covered by different polyvinyl chloride sheets. Owing to the supplementary design margins, the antenna impedance bandwidth remains covered. Moreover, the radiation patterns are measured in various elevation planes. Under standalone conditions, a radiation efficiency and a maximum gain of 74.3% and 5.8 dBi at 2.45 GHz and 48.1% and 2 dBi at 868 MHz are, respectively, obtained. Its omnidirectional coverage in the horizontal plane, stable performance on the inhomogeneous and biocompatible cork substrate and for various inhomogeneous superstrates, and its low-profile integration make the proposed antenna an excellent candidate for smart floors and smart houses

2008 Index IEEE Transactions on Control Systems Technology Vol. 16

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index