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Microwaves, Antennas & Propagation, IET

Issue 1 • Date February 2007

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Displaying Results 1 - 25 of 39
  • Editorial

    Publication Year: 2007
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (71 KB)  

    Presents an introduction to a special issue on metamaterials. The papers are very briefly described. In the mainstream metamaterial part of this issue, particular emphasis is placed on the so called left-handed, negative-reftactive-index (or negative index), or double negative (DNG) media. The second part of this issue concentrates on recent explorations and advances of EBG structures and related high-impedance surfaces View full abstract»

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  • Contemporary notes on metamaterials

    Publication Year: 2007 , Page(s): 3 - 11
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (217 KB)  

    The essence of the metamaterial concept from the structural point of view. Particular attention is paid to the macroscopic description of metamaterials and to the corresponding requirements and precautions for using that concept. General advantages of metamaterials are also pointed out. Next, the main research directions related to metamaterials are briefly overviewed and the key references are provided. Finally, the most probable sources of disagreement and misunderstanding within the field are summarised View full abstract»

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  • Antenna applications of negative-refractive-index transmission-line structures

    Publication Year: 2007 , Page(s): 12 - 22
    Cited by:  Papers (24)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1270 KB)  

    A number of new antenna-related applications that have recently been developed at the University of Toronto based on the concept of negative-refractive-index transmission-line metamaterials are reviewed. These include non-radiating phase-shifting lines that can produce either a positive or a negative phase-shift while exhibiting a broadband linear phase response, as well as compact and broadband series power dividers and associated planar series-fed printed dipole arrays with reduced beam-squinting. Moreover, a fully printed electrically small ring antenna featuring vertical polarisation and good radiation efficiency is also described View full abstract»

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  • Left-handed transmission lines at millimetre and sub-millimetre wavelengths

    Publication Year: 2007 , Page(s): 23 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (537 KB)  

    Co-planar strip (CPS) transmission lines, aimed at operating up to sub-millimetre wavelengths, were periodically loaded by lumped capacitances and inductances in series and shunt configuration, respectively. Under this condition, propagation on the line is backward with group and phase velocities of opposite signs. The transmission lines were fabricated onto a quartz substrate by e-beam patterning and thin film deposition, silicon nitride and gold layers, on a deep sub-micron scale (~200 nm). A direct evidence of left-handedness between 160 and 380 GHz was achieved via the tracking of phase advance in a differential phase experiment using electro-optic sampling. The comparison between modelling results by electromagnetic full wave circuit analysis and experiment was performed in the time and frequency domains. It shows a good agreement in the dispersion characteristics and ultra-fast variations in the transmitted signals. At last, we took benefit of a lumped element fitting approach in order to discuss of the frequency capability of this non-resonant approach View full abstract»

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  • Compensated circuit with characteristics of lossless double negative materials and its application to array antennas

    Publication Year: 2007 , Page(s): 29 - 38
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (599 KB)  

    A compensated circuit showing the characteristics of lossless double negative (DNG) materials is proposed and applied to an active integrated antenna array. A properly selected matching circuit produces the phase advance, which is characteristic of a left-handed wave (backward-wave), and the lossy resonant circuit generates the negative group velocity. An amplifier is used to compensate for the inherent loss of the resonant circuit, including its resistor. Then, a series-fed antenna array with a proposed DNG circuit is also designed and fabricated. It consists of two subarrays, each made of two aperture-coupled patch antennas, and the DNG circuit block inserted between the subarrays. In comparison to a conventional array, without the DNG circuit whose two subarrays are connected directly by a microstrip line, the proposed array shows a negligible beam squint and flat gain, over a considerable bandwidth of 11% View full abstract»

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  • Size reduction of microstrip patch antennas with left-handed transmission line loading

    Publication Year: 2007 , Page(s): 39 - 44
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (329 KB)  

    A procedure for designing an electrically small microstrip patch antenna (MPA) is developed, wherein the length of a side of the MPA is reduced to significantly less than a half-wavelength. The MPA is loaded with a resonant circuit equivalent to that of a left-handed transmission line to artificially increase the effective wavelength of the device, thus creating a resonance equivalent to, but at a lower frequency than the unloaded {10} mode. The field distribution in the loaded MPA remains relatively unperturbed, unlike the {0} mode case that attempts to decrease the size by introducing a shorting-post; consequently, very low cross-polarisation behaviour is observed. The theory to predict the full spectrum of resonant frequencies of the antenna is developed, with finite-difference time-domain simulations used to finalise the antenna design. Finally, an electrically small ((lambda/6)times(lambda/4)) and thin (<lambda/65) antenna is fabricated at 465 MHz using low-temperature co-fired ceramic technology and tested for key figures of merit, including the resonant frequency and radiation pattern. The shortened antenna not only shows performance comparable to a conventional unloaded MPA, but also exhibits good cross-polarisation. The loaded MPA achieved an area reduction of 83% as compared to an unloaded version View full abstract»

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  • Left-handed L-band notch bandstop filter with significantly reduced size

    Publication Year: 2007 , Page(s): 45 - 49
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    An innovative compact microstrip line left-handed (LH) L-band notch bandstop filter is presented, validated by full-wave simulations and demonstrated by experiments, showing that the size of the filter can be significantly reduced by employing the LH transmission line (TL) metamaterials. The proposed notch bandstop filter was constructed using coupled line coupler loaded with 90deg LH TL. The size of the fabricated LH filter is 4.4 times smaller than that of the filter loaded with -270deg conventional TL and nearly two times smaller than that of the filter loaded with -270deg meandered TL. The filter has a centre frequency of 1.164 GHz and a fractional bandwidth of 0.51%. The loaded quality factor of the filter is 197, indicating 64 and 97% increases in comparison with the conventional and meandered TL filters, respectively View full abstract»

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  • Bloch wave approach to the design of optimally matched non-effective medium composite right/left handed transmission lines

    Publication Year: 2007 , Page(s): 50 - 55
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    A simple method to design optimally matched composite right-/left-handed transmission lines (CRLH-TLs), based on the computation of the Bloch wave equivalent impedance of the corresponding unit cell circuit is presented. Although the matching of CRLH-TLs that can be considered as effective media is straightforward, it is shown that it is not the case for non-effective medium structures, which are also relevant realisations of this type of metamaterial in particular situations. Since the method does not rely on any assumptions on the parameters of the circuit, it is valid both for effective medium and non-effective medium CRLH-TLs. The reduction of the mismatch obtained with the proposed method also results in an improvement in the insertion loss and phase shift linearity in terms of S-parameters. Finally, we present some experimental validation of the benefits of the method by means of quartz-integrated CRLH-TLs realisations View full abstract»

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  • Channelled waves in anisotropic mesh metamaterials

    Publication Year: 2007 , Page(s): 56 - 64
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1153 KB)  

    Channelled waves in 2D periodic anisotropic L-C mesh metamaterials have been investigated. Circuit simulation and the newly developed analytical model of a unit cell have demonstrated full qualitative agreement for both lossless and lossy cases. Isofrequencies for a lattice unit cell and the circuit simulations of finite meshes have shown that propagating waves are channelled from a point source as pencil beams which can travel only along specific trajectories. The beam direction varies with frequency, and at resonance frequency omega=1/(LC)1/2, the phase and group velocities of the transmitted wave are orthogonal. The effect of losses was explored, and it is shown that losses can cause qualitative changes of the channelled wave type. It is shown that the channelled waves do not follow the laws of geometrical optics (Snell's law, specular reflection and so on) at the interfaces of L-C meshes but are governed by the conditions of phase synchronism and impedance matching. Only in the special case of dual L-C and C-L meshes with the interface parallel to the axis of rectangular grid excited at the resonance frequency (X=1) do the channels follow the trajectories of optical rays. A planar mesh test cell has been designed and applied to retrieving the unit cell L-C parameters from the S-parameter measurements View full abstract»

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  • Forward and backward leaky wave radiation in split-ring-resonator-based metamaterials

    Publication Year: 2007 , Page(s): 65 - 68
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    The ability of planar left-handed metamaterials (LHMs) based on split-ring resonators (SRRs) to radiate backwards in a certain frequency range, as predicted by theory, is demonstrated. A comparison between an LHM and a negative permeability metamaterial in terms of the experimental backward and forward radiation cones (which are related to their dispersion diagrams) is carried out. The results of this work open the possibility to use SRRs as miniaturised and flexible radiating elements for antennas and arrays in wireless communication applications View full abstract»

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  • Nonlinear Josephson left-handed transmission lines

    Publication Year: 2007 , Page(s): 69 - 72
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    In the paper, a new nonlinear left-handed transmission line (NLHTL) that incorporates arrays of Josephson junctions (JJs) is proposed. The nonlinearity of the newly developed Josephson left-handed transmission line (JLHTL) is due to the highly nonlinear nature of the JJs that provide the shunt inductances required to realise an LHTL. The current-voltage relationship of an array of JJs is utilised to realise an inductively tunable LHTL. Dispersion analysis along with the scattering parameters of the JLHTL are presented to study the left-handed behaviour of the JLHTL. Finally, harmonic generation of the proposed JLHTL is studied View full abstract»

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  • Miniaturisation of planar microwave circuits by using resonant-type left-handed transmission lines

    Publication Year: 2007 , Page(s): 73 - 79
    Cited by:  Papers (17)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (718 KB)  

    It is demonstrated that planar microwave circuits and components such as impedance inverters or power dividers, among others, can be compacted by using artificial left-handed transmission lines in their designs. Key to this size reduction is the possibility to control the electrical characteristics of these lines (namely electrical length and image impedance) over wide margins by means of a single cell structure. It consists of a microstrip line section with a series capacitive gap etched in the conductor strip and loaded with a complementary split rings resonator etched in the ground plane. A recently reported model of the artificial line is used as a first step in the design of the desired devices. To demonstrate the viability of the approach, several prototype device examples are provided, that is a 90deg impedance inverter and several power dividers with different topologies. A 50% size reduction (as compared to conventional devices) has been achieved by implementing the devices in conventional low loss microwave substrates, but further levels of miniaturisation can be obtained if the devices are fabricated on advanced technologies such as low temperature co-fired ceramic or multi chip module-deposited, among others View full abstract»

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  • Experimental study of a bi-periodic magnetoinductive waveguide: comparison with theory

    Publication Year: 2007 , Page(s): 80 - 83
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    Magnetoinductive waves propagating along a line consisting of two kinds of metamaterial elements are studied. Both elements are made up by the same metallic loop but are loaded by different capacitors resulting in different resonant frequencies. The dispersion characteristics are derived from phase and amplitude measurements for the cases when the line consists of (i) identical elements and (ii) of alternating elements. Both planar (elements in the same plane as the axis of the line) and axial (elements perpendicular to the axis of the line) configurations are investigated. It is shown that in the bi-periodic arrangement of the elements, the dispersion curves have a forward wave in the lower frequency branch and a backward wave in the upper frequency branch independent of the configuration whether it is planar or axial. Comparisons between theoretical and experimental results show good agreement View full abstract»

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  • Stability of surface integral equation for left-handed materials

    Publication Year: 2007 , Page(s): 84 - 89
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (269 KB)  

    In recent years, left-handed materials (LHMS) have been a hot and debated research topic. Electromagnetic simulation is usually performed for prediction as well as for design. The stability of the surface integral equation method through an insightful and rigorous procedure is analysed. The conclusion is that the PMCHWT formulation at perfectly matched LHM-RHM interface has stability problem, which comes from the plasmon resonance condition. Adding a small amount of loss can greatly improve the condition number of the matrix. Physical and consistent numerical results are shown followed by a brief conclusion View full abstract»

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  • Experimental investigation of reflection characteristics of left-handed metamaterials in free space

    Publication Year: 2007 , Page(s): 89 - 93
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The transmission and reflection characteristics are presented of a one-dimensional (1D) left-handed metamaterial (LHM) and its constituents, split ring resonator and thin wire arrays. A well-defined left-handed transmission band with a peak value of -7.2 dB is obtained at frequencies where effective permittivity and permeability are both negative. A sharp dip (-34.5 dB) at the reflection spectrum of 1D ordered LHM is observed. The frequency of ultra-low reflection did not change considerably for another LHM with a different thickness, meaning that the low reflection is not because of the thickness resonance but rather the impedance-matching of LHM at the surface. Disorder in LHM structures is shown to affect the reflection characteristics View full abstract»

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  • Influence of split ring resonators on the properties of propagating structures

    Publication Year: 2007 , Page(s): 94 - 99
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (623 KB)  

    The study of a 50 Omega microstrip line and microstrip resonators loaded with resonant elements called split-ring resonators (SRRs) is presented. The two different filtering phenomena observed lead to make an analogy with those observed when waveguides are loaded with these elements. So, in order to make this analogy, the different results obtained with the SRRs loaded in a propagating and an under cut-off waveguide are shown. Then, another technique to achieve and even improve these results is presented. The technique consists of using, respectively, a 50 Omega microstrip line and capacitive-gap-coupled microstrip resonators instead of the propagating and under cut-off waveguides. The numerical and experimental results obtained with the two structures (waveguides and microstrip lines) are compared and discussed. This study shows that the combination of SRRs with guiding structures helps in the design of compact structures, but an enhancement of the performances needs a better fabrication accuracy View full abstract»

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  • Efficient FDTD method for analysis of mushroom-structure based left-handed materials

    Publication Year: 2007 , Page(s): 100 - 107
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1091 KB)  

    A finite-difference time-domain method, combined with thin-wire and thin-slot algorithms, which is used to analyse a metamaterial based on periodic mushroom structures, is proposed. This proposed method is suitable for analysing problems involving large structures with fine structural details. Several composite right/left handed (CRLH) metamaterial mushroom-based structures are investigated. A 19 times 8 flat lens and a parabolic lens structure composed of 410 unit mushroom cells are investigated and they demonstrate negative-refractive-index characteristics while operating in the LH region. The simulation and measurement results of one- and two-dimensional CRLH mushroom-based structures are compared. The periodic analysis for mushroom structures is also introduced. Only a single unit mushroom cell is required to present the phenomena of infinite periodicity with periodic boundary conditions View full abstract»

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  • Microwave focusing and beam collimation using negative index of refraction lenses

    Publication Year: 2007 , Page(s): 108 - 115
    Cited by:  Papers (4)  |  Patents (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1054 KB)  

    Negative index of refraction materials (NIMs) were first postulated by Veselago in 1968 and have recently been realised using structures formed with rings and wires deposited on printed circuit boards. The proof of the existence of negative index of refraction was established using a Snell's law experiment with a wedge. The predicted and measured refraction angles were found to be consistent for a negative index material and in excellent agreement with the theoretical expectations. For microwave lenses NIMs have the advantage of being lighter, having better focusing properties and potentially lower aberrations. Simulation and experimental results on NIM configurations including gradient index of refraction and spherical 3D lenses are presented. Both focusing and beam collimating applications will be considered. These results will be compared to normal positive index of refraction material lenses View full abstract»

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  • At and below the chu limit: passive and active broad bandwidth metamaterial-based electrically small antennas

    Publication Year: 2007 , Page(s): 116 - 128
    Cited by:  Papers (24)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    The solution to the canonical problem of a radiating infinitesimal electric dipole antenna that is centred in a multilayered, concentric metamaterial-based spherical shell system is presented. It is demonstrated that when this system is electrically small, a specifically designed homogenous and isotropic epsilon-negative (ENG) layer can function as a distributed matching element to the antenna enabling a resonant radiation behaviour. A finite element model of the corresponding centre-fed cylindrical dipole antenna-based resonant system confirms that such designed ENG-based spherical layers can act as a distributed matching element, which can be optimised to produce a reactance free, resistively matched and, hence, efficient radiating system. Several limits on the dispersion properties of the homogenous and isotropic ENG media used in these matching layers are considered and their impact on the bandwidth of these resonant systems is established. Although the dispersionless resonant antenna-ENG system has a bandwidth substantially below the Chu limit, the bandwidths of the corresponding dispersive systems are shown to be at or just slightly below the Chu limit. An analytical model of an idealised gaseous plasma-based ENG layer sandwiched between two glass layers, a potential realisation of these metamaterial-based ENG spherical shell systems, is introduced and its solution is used to study these efficiency and bandwidth issues further. Resonant systems based on active ENG metamaterial layers realised with two types of idealised gain medium models are shown to have bandwidths that approach the idealised dispersionless medium values and, consequently, are substantially below the Chu limit View full abstract»

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  • Analysis of guided and leaky waves excited by an infinite line source in metamaterial substrates

    Publication Year: 2007 , Page(s): 129 - 136
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    The properties of electromagnetic modes having real and complex propagation constants are thoroughly examined in this article by considering the excitation of a metamaterial slab having both negative values of dielectric permittivity and magnetic permeability. The conditions of existence of modes are investigated and the excited corresponding modes are analysed. Several types of waves are examined and their corresponding dispersion properties are derived View full abstract»

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  • Use of conjugate dielectric and metamaterial slabs as radomes

    Publication Year: 2007 , Page(s): 137 - 143
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1114 KB)  

    An interesting application of left-handed metamaterials is proposed and numerically verified. Specifically, a structure consisting of a conventional dielectric slab adjacent to a metamaterial slab of the same width but of opposite material characteristics, is used as a radome. The behaviour of the structure for normal as well as for oblique incidence is considered. The results are satisfactory in both cases. It is shown that cylindrical structures similar to the aforementioned straight structures could also be used as radomes. However, the behaviour of the structure is non-reciprocal for incoming and outgoing waves. The dispersive finite-difference time-domain method is applied to study all the structures and the numerical results verify that the straight conjugate slabs are transparent in normal incidence and reduce the reflections for oblique incidence, which are the desirable characteristics for a radome View full abstract»

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  • Evanescent surface-wave modes in a slab with application to miniaturised waveguide components

    Publication Year: 2007 , Page(s): 144 - 149
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Characteristics of surface-wave modes in a slab with either negative permittivity or negative permeability are considered. It is shown that this kind of slab is a monomode structure which supports TM mode when the permittivity is negative and TE mode when the permeability is negative. It is shown that tightly bound surface-wave modes exist, also backward waves, in a slab with small thickness. These surface-wave modes will certainly have applications in trying to miniaturise waveguide components in microwave techniques and in optics. As an example, characteristics for a planar plasma waveguide are given View full abstract»

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  • Doubly periodic volume-surface integral equation formulation for modelling metamaterials

    Publication Year: 2007 , Page(s): 150 - 157
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (862 KB)  

    A generalised volume-surface integral equation is extended by way of the periodic Green's function to model arbitrarily complex designs of metamaterials consisting of high-contrast inhomogeneous anisotropic material regions as well as metallic inclusions. The unique aspect of the formulation is the integration of boundary and volume integral equations to increase modelling efficiency and capability. Specifically, the boundary integral approach with equivalent surface currents is adopted over regions consisting of piecewise homogeneous materials as well as metallic perfect electric/magnetic conductor inclusions, whereas the volume integral equation is employed only in inhomogeneous and/or anisotropic material regions. Because the periodic Green's function only needs to be evaluated for the equivalent surface currents enclosing an inhomogeneous and/or anisotropic region, matrix fill time is much less as compared to using a volume formulation. Furthermore, the incorporation of curvilinear finite elements allows for greater geometrical modelling flexibility for arbitrarily shaped high-contrast regions found in typical designs of engineered metamaterials View full abstract»

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  • GA/FDTD technique for the design and optimisation of periodic metamaterials

    Publication Year: 2007 , Page(s): 158 - 164
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    An efficient and powerful full-wave electromagnetic technique is presented to characterise and design periodic metamaterial structures. First, the spectral finite-difference time-domain (FDTD) method with periodic boundary conditions and uniaxial perfect matched layer is employed to predict the performance of a mushroom-like artificial magnetic conductor (AMC) surface and further extended to characterise a negative-refractive-index material consisting of lumped and distributed transmission-line elements. Then, a new computational technique is developed to design and optimise periodic metamaterial structures by integrating the spectral FDTD method with a genetic algorithm (GA), namely the micro-genetic algorithm. This computational technique is successfully applied to design and optimise single-band and dual-band AMC structures consisting of a frequency-selective surface and a ground plane. It is demonstrated that the GA/FDTD technique is a very effective approach for the design and optimisation of periodic metamaterial structures consisting of dielectrics and conductors of arbitrary configurations View full abstract»

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  • Broadband transmission below the cutoff frequency of a waveguide loaded with resonant scatterer arrays

    Publication Year: 2007 , Page(s): 165 - 169
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (471 KB)  

    A computer-aided method for the design of waveguide structures loaded with the arrays of metamaterial cells is described. Broadside coupled split ring resonators and Omega scatterers are chosen as the resonant metamaterial cells. By optimisation of the resonator geometry, the bandwidth of the transmission range below the cutoff frequency of the waveguide is enlarged compared with the results reported in the literature. The modes propagated below the waveguide cutoff possess a passband of the order of 30-50% and can be of the backward as well as of the forward type. The presented optimisation approach is based on the eigensolver simulations of a metamaterial unit cell. The designed metamaterial arrays are fabricated and measured. The experimental results are compared with the simulations validating the proposed design approach View full abstract»

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