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Microwaves, Antennas & Propagation, IET

Issue 3 • Date June 2007

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Displaying Results 1 - 25 of 42
  • Novel digital and analogue tunable lowpass filters

    Publication Year: 2007 , Page(s): 549 - 555
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (707 KB)  

    The paper presents a new concept for implementing tunable lowpass filters by employing slot resonators etched in the ground plane. When RF MEMS switches are used to short-circuit the slots in the ground plane, the effective length of the slots can be varied to achieve tunability at discrete frequencies. The concept is demonstrated by considering 4-slot lowpass filters. Continuous tuning is achieved by replacing switches with varactors as tuning elements. A varactor tuned lowpass filter was built and tested. Simple transmission line models for the proposed structure are also presented. The measured results are in good agreement with simulations confirming the validity of the proposed model. The experimental lowpass filters exhibit superior RF performance which consists of a low insertion loss and a large tuning range. The insertion loss is 0.6 dB for both the digital and the analogue tunable filters, while the achievable tuning range is 44% for the digital tunable filter and 22% for the analogue tunable filter. A much wider tuning range is obtained by combining digital and analogue tuning in one circuit View full abstract»

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  • Compact wideband antenna for wireless communications

    Publication Year: 2007 , Page(s): 556 - 560
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (489 KB)  

    A compact dual-band printed wire antenna for applications in wireless communications is presented. An additional shorted parasitic element to the F-shaped wire antenna is introduced to achieve a dual-band operation. As an example, a new antenna was designed and fabricated for wireless local area network applications that operate in the 2.4 and 5.2/5.8 GHz bands. The prototyped antenna offered two separate measured impedance bandwidths of 700 (2.35-3.05 GHz) and 2150 MHz (3.95-6.1 GHz), for a return loss less than -10 dB. A measured antenna gain of 1.78-1.9 dBi was observed across the lower band, whereas a measured antenna gain of 3.9-4.4 dBi was observed across the upper band. The measured radiation patterns were stable across the passband View full abstract»

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  • Perfectly anisotropic impedance boundary

    Publication Year: 2007 , Page(s): 561 - 566
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (117 KB)  

    The concept of a perfectly anisotropic boundary (PAB) is defined in terms of a surface impedance dyadic without an isotropic component. Realisation of PAB in terms of a slab of anisotropic metamaterial is suggested. It is shown that PAB can serve as a simple rotatable polarisation transformer, transforming a linearly polarised field to a field with given elliptic polarisation and handedness, or conversely. It is also shown that, unlike at a regular impedance boundary, a PAB can simultaneously support two orthogonally polarised surface waves propagating in certain directions along the boundary View full abstract»

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  • Passive microwave filter tuning using bond wires

    Publication Year: 2007 , Page(s): 567 - 571
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (238 KB)  

    A practical method is proposed to tune microwave planar filters. When the circuit is fabricated, a number of additional capacitive patches and inductive lines are patterned close to the filter. These patches and lines can be connected to the filter by bond wires to tune the filter response. By replacing the traditionally used tuning screws with these bond wires, the package for a microwave filter can be much more compact, and the mechanical reliability of the tuned filters can be improved. To demonstrate the method, a three-pole microstrip filter is fabricated on a Duroid substrate. The additional capacitive patches and inductive lines are also patterned on the same substrate close to the filter. By connecting the patches and the lines to the filter with bond wires, the centre frequency of the three-pole filter is easily tuned by -7% and+7%, respectively, and can be tuned to an arbitrary value in a wider range. The return loss of the filter is tuned from 15 dB to better than 20 dB in the passband at the same time. It is also found that the bond wire has introduced negligible additional loss View full abstract»

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  • Compact broadband coplanar waveguide-fed curved quasi-Yagi antenna

    Publication Year: 2007 , Page(s): 572 - 574
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (317 KB)  

    A novel uniplanar coplanar waveguide-fed quasi-Yagi antenna is presented. The originality of this design is because of its feed selection and its elliptical structure and in doing so achieving a wide bandwidth and compact size. An X-band prototype is developed and measures a bandwidth of 40%, with 3.2 dBi gain and 11 dB front-to-back ratio measured at 10 GHz. The antenna is realised on a high dielectric constant substrate and is compatible with monolithic microwave integrated circuits and solid-state devices View full abstract»

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  • Dispersion characteristics of a rectangularly corrugated cylindrical slow-wave structure driven by a non-relativistic annular electron beam

    Publication Year: 2007 , Page(s): 575 - 579
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (209 KB)  

    The dispersion relation of a rectangularly periodic cylindrical slow-wave structure (SWS) with an annular electron beam of energy <100 keV and current around 200 A has been derived and solved numerically. This type of system is typically used in backward wave high-power microwave devices and linear accelerators. The dispersion relation is analysed for both the cold structure (for zero beam current) and structure with an annular beam. The cold structure dispersion relation is characterised by the real value of frequency and wavenumber. When an electron beam propagates through the structure and the beam energy and current are sufficient to produce instability, microwave radiation results. The strength of this radiation can be qualitatively approximated from the temporal growth rate of the instability, which is defined by the imaginary values of the frequency corresponding to the complex conjugate roots of the dispersion relation. The temporal growth rate for various beam parameters has been calculated. The proposed SWS is very easy to be fabricated and can be used in the real experiments for generating high-power microwaves View full abstract»

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  • Design and optimisation of a high-frequency EMC wideband horn antenna

    Publication Year: 2007 , Page(s): 580 - 585
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A new approach for the design of high-frequency electromagnetic compatibility (EMC) broadband double-ridged horn (DRH) antennas is presented. In this approach, first a conventional DRH antenna at 1-18 GHz frequency band is considered. Using a thorough sensitivity analysis of different structural parameters of the 1-18 GHz DRH antenna, several modifications are applied to this antenna to overcome its deficiencies especially in its radiation pattern at higher frequencies. The final achieved design is then scaled up in the frequency to arrive at a design suitable for higher frequency ranges. A wideband DRH antenna for 18-40 GHz frequency band is then designed using this approach. The lower frequency ratio of 1:2.2 in the new antenna as opposed to the 1:18 ratio in the conventional antenna permits us to choose the best frequency window for the scaling up process. Besides, an optimisation technique is employed to further improve the antenna performance to meet the design goals over the entire new frequency band, that is, to have a single main lobe directed along the horn axis without any deterioration, and to have acceptable broadband gain with the minimum of 10 dB, and voltage standing wave ratio (VSWR) of less than 1.5. The final design which is more compact compared with the other commercial antennas has been used to make a prototype antenna. Measurements show that the built prototype meets the design goals very well View full abstract»

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  • Errors in near-field radioholography

    Publication Year: 2007 , Page(s): 586 - 591
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (237 KB)  

    Formulae are given for the aperture plane phase errors which are incurred in near-field radioholography of reflector antennas when a simple Fresnel correction is used. Approximate analytic expressions are derived for circular data windows and antennas with parabolic illumination taper. Infocus and defocused cases are treated. Numerical simulations are used for estimating errors for square data windows View full abstract»

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  • Polarisation control of a loop antenna by PIN diodes

    Publication Year: 2007 , Page(s): 592 - 596
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (411 KB)  

    A wire loop antenna with two electronic switches is introduced to control polarisation (left-hand, right-hand or linear polarisation). The loop is fed through an electromagnetically coupled monopole antenna. The loop and the monopole are located on a ground plane. The switching circuit with PIN diodes is installed near the feed point of the monopole to obtain symmetric radiation patterns. Good axial ratio and impedance characteristics are obtained. The experimental results show the capability of the polarisation control by electronic switches View full abstract»

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  • Stability analysis of the Mur's absorbing boundary condition in the alternating direction implicit finite-difference method

    Publication Year: 2007 , Page(s): 597 - 601
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (142 KB)  

    The stability analysis of the Mur's first order absorbing boundary condition (ABC) in the alternating direction implicit finite-difference time-domain (ADI-FDTD) method is presented. The theoretical stability analysis of this scheme is studied by deriving the amplification matrix. The effect of wave propagation direction on the stability of this scheme is investigated. From the stability analysis, it is found that the Mur's first order ABC in the ADI-FDTD method will be unstable. The instability of the scheme is validated by means of actual numerical simulations View full abstract»

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  • Path loss models based on stochastic rays

    Publication Year: 2007 , Page(s): 602 - 608
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (132 KB)  

    Two-dimensional percolation lattices are applied to describe wireless propagation environment, and stochastic rays are employed to model the trajectories of radio waves. First, the authors derive the probability that a stochastic ray undergoes certain number of collisions at a specific spatial location. Three classes of stochastic rays with different constraint conditions are considered: stochastic rays of random walks and generic stochastic rays with two different anomalous levels. Subsequently, the authors obtain the closed-form formulation of mean received power of radio waves under non-line-of-sight conditions for each class of stochastic ray. Specifically, the determination of model parameters and the effects of lattice structures on the path loss are investigated. The theoretical results are validated by comparison with the experimental data View full abstract»

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  • Finite-element time-domain modelling of plane wave scattering by a periodic structure using an exact boundary condition

    Publication Year: 2007 , Page(s): 609 - 616
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (369 KB)  

    A two-dimensional singly-periodic structure, at plane wave oblique incidence, is modelled using the finite-element time-domain method. Over the non-periodic boundaries of the computational domain, an exact Floquet modal absorbing boundary condition is developed, in detail, for the finite element method in the time domain. The proposed formulation is validated by comparing its results with that of the finite-element frequency-domain method and with independently obtained published results. Very accurate numerical results, over a wide frequency range and incident angle range, are obtained for both transverse electric and transverse magnetic polarised plane wave illuminations View full abstract»

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  • Re-examination of analytical models for microwave scattering from deciduous leaves

    Publication Year: 2007 , Page(s): 617 - 623
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (219 KB)  

    This paper presents an examination of classical scattering models for radar cross sections of deciduous leaves, such as the generalised Rayleigh-Gans (GRG) model and the physical optics (PO) model. The PO model employs the resistive sheet approximation in this study. The validity regions of the analytical models for microwave scattering from deciduous leaves are investigated by comparison with the precise numerical results of the method of moment. It was found that the GRG and PO models extend their validity regions for estimating the scattering amplitudes as the thickness of a lossy dielectric disk decreases. The GRG and PO models can be used alternatively for computing the scattering matrices of natural deciduous leaves at microwave frequencies regardless of the size of the leaves, because of the very small thickness of the leaves (0.2-0.4 mm) View full abstract»

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  • 24 GHz automotive radar planar Luneburg lens

    Publication Year: 2007 , Page(s): 624 - 628
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (295 KB)  

    A planar Luneburg lens whose permittivity distribution is modified by two types of hole density control in the central region and by dielectric thickness control in the edge region is reported. The lens was designed to operate at 24 GHz in Transverse Electromagnetic (TEM) mode. Experimental radiation patterns show good agreement with the simulation. The measured 3 dB beamwidth of the vertical polarised H-plane pattern is 5deg with 14 dB gain at 24 GHz for a 12.2lambda, 15.24 cm diameter lens, cross polar levels were below -30 dB. Its small size and lightweight, 53% of material is removed, and better than 20% bandwidth makes it useful for vehicular use in the 24 GHz unlicensed Industrial, Scientific, Medical (ISM) equipment band and for 24 GHz short range radar applications View full abstract»

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  • Calibration of smart antenna systems: measurements and results

    Publication Year: 2007 , Page(s): 629 - 638
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (663 KB)  

    Smart antennas (SAs) are viewed as a candidate enabling technology for modern wireless communication systems to increase network capacity and facilitate location-based services. By conducting measurements on an SA test-bed, the signal distortion introduced by the implementation of a practical system can be analysed. This distortion can have significant impact on the estimation of signal wavefronts. Measurements have been conducted at the system, sub-system and component levels, using an SA developed for this purpose and employing a uniform circular array. This has enabled the error introduced by an implemented system to be examined. Calibration procedures are developed to overcome these implementation limitations. The cause and effects of these errors are examined, and system manufacturing tolerances and temporal thermal effects on the analogue sub-systems are shown to be the major contributor to this error; these results are presented and analysed View full abstract»

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  • Short-circuit equivalence between rectangular waveguides of regular sidewalls (rectangular waveguide) and sidewalls of cylinders (substrate-integrated rectangular waveguides), plus its extension to cavity

    Publication Year: 2007 , Page(s): 639 - 644
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (350 KB)  

    Substrate-integrated rectangular waveguide (SIW) is a rectangular waveguide (RW) with two sidewalls of cylinders (vias) instead of solid walls connecting the solid wall of the top and bottom plates. An equivalence formula between their widths has been derived based on the work by Che et al., 2005 [2005 Asia-Pacific Microwave Conference, Suzhou, China, December 4-7, 2005, pp. 296-299]. The authors have derived the equivalence formula between the locations of the corresponding short circuits by cylinder walls and by the solid wall. An extension of latter is the equivalence between resonance cavities of SIW and RW. Such equivalences are convenient for the design of small waveguides, of millimeter wave, in a multilayer circuit structure, such as the low-temperature co-fired ceramic. Some numerical simulations and experiments have been carried out to demonstrate the validity of the proposed approaches View full abstract»

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  • Efficient implementation of the stretched co-ordinate perfectly matched layer based on the Z-transform method

    Publication Year: 2007 , Page(s): 645 - 650
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    A novel, efficient and unsplit-field algorithm for implementing the stretched co-ordinate perfectly matched layer (SC-PML) based on the Z-transform method is discussed in detail for truncating the finite-difference time-domain lattices. The advantage of the proposed algorithm is that fewer auxiliary variables are required in the PML regions and thus the memory requirement is less than that of other implementations of the SC-PML. Four numerical tests have been carried out to validate the proposed algorithm. It is demonstrated in the numerical tests that the proposed algorithm provides good absorbing performance, requires less computational time and is stable View full abstract»

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  • Design of a microstrip filter using multiple capacitively loaded coupled lines

    Publication Year: 2007 , Page(s): 651 - 657
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (171 KB)  

    A method to design a microstrip filter has been proposed. The multiple capacitively loaded coupled lines are adopted for the design of the microstrip filter. The filter shows different stopband behaviour with respect to even or odd total number of resonators. The transmission zeros may be located around the lower, higher or both regions of the passband's skirt. The coupling among the capacitively loaded lines can produce another transmission zero particularly in the higher stopband. A bandpass filter and a duplexer utilising these features are designed. The equivalent model is also proposed to illustrate the filter's coupling among these capacitively loaded coupled lines. The design has been verified by experimental results View full abstract»

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  • Circularly polarised proximity-fed microstrip antenna with polarisation switching ability

    Publication Year: 2007 , Page(s): 658 - 665
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (619 KB)  

    The authors propose a design of a circularly polarised proximity-fed microstrip antenna having polarisation switching ability. The proposed antenna has a simple structure, consisting of a truncated-corners square patch in the same plane with a microstrip feed line extended beyond the patch edge, pin diode and a pad connected to a ground by a conducting post. The diode, which is inserted between the end of the feed line and a pad, is used to control feed line termination. By turning the diode on or off, this antenna can radiate either right hand or left hand circular polarisation. Furthermore, we present a technique to improve the input characteristics of the antenna. It involves two diode-controlled tuning stubs connected in shunt with the feed line. Finally, a discussion on how the diode characteristics affect the structure and results of the antenna is given. All analyses are carried out using finite-difference time-domain technique and confirmed by measurements in the 5 GHz band. A good agreement between the simulated and measured results was obtained View full abstract»

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  • Estimation of time of arrival of UWB multipath clusters through a spatial correlation technique

    Publication Year: 2007 , Page(s): 666 - 673
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (698 KB)  

    This study estimates the time of arrival (TOA) of ultra wideband multipath components (MPCs) by analysing the spatial correlation of multipath signals captured by a 7times7 antenna array. In this study, both line-of-sight and non-line-of-sight radio propagation paths were considered. Each power-delay profile bin from all the array positions was used to calculate the spatial correlation between itself and the adjacent receiving point bins. Consequently, some MPC time delays and clusters, associated with high correlation values, were selected and compared with the TOA computed by the Sensor-CLEAN algorithm. A close agreement of the TOA estimated by both techniques was obtained. Finally, multipath cluster distributions and clustering model parameters are presented and compared with previously published results View full abstract»

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  • Comparative robustness study of planar antennas

    Publication Year: 2007 , Page(s): 674 - 680
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    Is it possible to produce a planar dipole-like antenna with a reduced conductive area without any loss in either robustness or performance? The objective is to reduce the amount of expensive conductor to be used when applying a meshing technique to the printing of antennas. In this context, robustness means that the characteristics are maintained when the antenna is damaged, for example if it is scratched. This is particularly important for radio frequency identification tags in logistic systems. A general antenna robustness evaluation methodology, based on numerical simulations of a large number of randomly damaged antennas, is used for the antenna comparisons. The antenna performance degradation, based on the return loss (S11) at 868 MHz, is monitored for some basic planar antennas. Finally, we show that it is possible to produce robust low-cost antennas using wire replacements for the solid planar antennas and thus, provided that the robustness requirement is moderate, replace the solid antenna with a thin conductor analogue View full abstract»

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  • A comprehensive study on the planar type of goubau line for millimetre and submillimetre wave integrated circuits

    Publication Year: 2007 , Page(s): 681 - 687
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Modifications of the traditional Goubau line into its planar type for implementation to integrated circuits of millimetre and submillimetre waves are studied in frequency range 100-400 GHz. Features and performances of this new type of transmission lines are studied for different line configurations, different dimensions and new materials with low dielectric constants. To improve the performance of this type of transmission line, perforated dielectrics or new dielectrics are used to reduce the permittivity of the supporting and adjacent slabs. Selections of line parameters are demonstrated and compared. Both miniature hybrid microwave integrated circuit and microwave integrated circuit compatible configurations are studied and discussed. Some results of characteristic impedance of this type of lines are also reported View full abstract»

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  • Compact bandpass filters in coplanar strip lines

    Publication Year: 2007 , Page(s): 688 - 692
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    The authors describe a compact bandpass filter design implemented in asymmetric coplanar strip lines. For initial demonstration, it was built on print circuit boards using modified two-pole Butterworth bandpass filter topology. The novel filter design does not use bonding wires, vias or any interconnecting structure. It is not based on quarter wavelength sections either. It uses the creation of an electrode pattern on the coplanar strip electrodes to emulate an equivalent circuit. The pattern is fine-tuned using full-wave simulations. Bandpass filters for 2.4 GHz ISM (Industrial, Scientific and Medical) and 5.15-5.85 GHz UNII (Unlicensed National Information Infrastructure) bands were designed, fabricated and measured. Measurement responses agree well with full-wave simulation results. The electrode pattern can be scaled for different centre frequency and improved with fine-tuning procedure. For chip-level implementation, the filter size can be greatly reduced because of much smaller minimum electrode width View full abstract»

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  • Electromagnetic modelling and optimisation of a planar holographic antenna

    Publication Year: 2007 , Page(s): 693 - 699
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    An electromagnetic model for the simulation of the H-plane radiation pattern performance of a class of planar holographic antennas is introduced. The appropriateness of the model, and its use in the optimisation and design of such antennas, is established experimentally View full abstract»

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  • Dual-grid finite-difference time-domain scheme for the fast simulation of surrounded antennas

    Publication Year: 2007 , Page(s): 700 - 706
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    A new finite-difference time-domain (FDTD) multiresolution strategy for surrounded antenna analysis is presented. The dual-grid FDTD (DG-FDTD) is divided into two FDTD simulations using different grids. Indeed, the antenna is firstly simulated without its environment using a finely discretised FDTD in order to determine its main characteristics and save its primary radiation. In a second step, this saved field is used as the excitation of a coarse FDTD to simulate the antenna with its environment. The application of the DG-FDTD to an ultra wide-band problem is discussed, and the DG-FDTD turns out to be an accurate and fast tool to simulate various antenna configurations. Furthermore, this method remains stable along the computational time, and is easy to implement in a classical FDTD scheme View full abstract»

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