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Microwaves, Antennas & Propagation, IET

Issue 11 • Date November 2010

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Displaying Results 1 - 25 of 35
  • Fast antenna pattern synthesis using the variational method

    Publication Year: 2010 , Page(s): 1689 - 1697
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (625 KB)  

    The radiation pattern is usually a factory set characteristic of telecommunication equipment. By using an antenna array, the radiation pattern can be shaped in order to optimise the covered region. Antenna pattern synthesis consists of determining the phase and the amplitude to apply to each radiating element of the network for obtaining the targeted radiation pattern. A radiation pattern synthesis technique based on the variational method is presented. The goal is expressed in terms of antenna radiation pattern and special attention is given to the computation time. We calculate an optimised mask function from specifications obtained during a surroundings learning step. The resulting radiation pattern is optimised in terms of power waste. Simulated and measured radiation patterns are presented in order to illustrate the performances of the method. The speed of convergence makes this method well suited to systems where radiation patterns must be modified in real time. View full abstract»

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  • Self-assembly of three-dimensional Au inductors on silicon

    Publication Year: 2010 , Page(s): 1698 - 1703
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (401 KB)  

    Integration of inductors into high-frequency silicon circuits currently comes at the expense of a low-quality factor (Q), mainly because of electromagnetic interactions with the underlying substrate. Various fabrication methods for high Q inductors have been proposed, but poor compatibility with standard semiconductor process technology is a common problem. A promising technique involving in-plane fabrication and surface tension self-assembly to the vertical orientation has been previously reported for copper inductors. Here, a complementary metal-oxide-semiconductor (CMOS)-compatible and lead-free version of this process, with improved reproducibility, is reported, using Au as the inductor material. A 4 nH meander inductor is fabricated and tested as a demonstrator, showing significant increase of Q upon rotation. View full abstract»

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  • Wideband integrated feeding system for a dual polarisation sinuous antenna

    Publication Year: 2010 , Page(s): 1704 - 1713
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1027 KB)  

    The objective of this work is to demonstrate the achievability of integrating a feeding system to the radiating part of a wideband dual polarised antenna. To reach this objective, a wideband microstrip-to-coplanar stripline (CPS) balun has been developed. This balun configuration is suitable for integration with planar balanced antennas in a compact form. The performance of this balun is investigated over a wide frequency range by comparison between measured and simulation results. The measured return and insertion loss of the balun in back-to-back configuration exhibit a wideband performance between 3 and 8 GHz. In order to validate the proposed balun potentiality, it has been employed to feed a wideband single polarised sinuous antenna in a compact configuration. A measured return loss better than 10 dB from 2.5 to 5.6 GHz was observed with a sinuous antenna in single polarisation mode. The radiation patterns show a good symmetrical directivity in the E- and H-planes and a cross polarisation level better than 10 dB in the frequency bandwidth. Finally, a wideband dual polarised CPS-fed antenna with an integrated configuration has been designed. Although the impedance bandwidth obtained for the dual polarised sinuous geometry (measured return loss better 10 dB from 3.7 to 7.3 GHz) was larger than the single polarisation, the radiation patterns were not symmetrical in the entire frequency bandwidth and some small distortions were observed. In conclusion, the authors have demonstrated that it is possible to integrate a feeding system very close to the radiating part of a wideband dual polarised antenna. View full abstract»

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  • Small printed inverted-L monopole antenna for worldwide interoperability for microwave access wideband operation

    Publication Year: 2010 , Page(s): 1714 - 1719
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (771 KB)  

    A small-size printed inverted-L monopole wideband antenna for mobile application is presented. The antenna is simply structured with an L-strip, which occupies a small area of 10×14 mm2 on the top portion of the substrate. A simple matching circuit using lumped elements is used to introduce two resonance frequencies and to further enhance the bandwidth. The proposed antenna achieves a 10 dB impedance bandwidth from 2.23 GHz to more than 4 GHz, which can cover the WLAN2400 and WiMAX2300/2500/3500 operation bands, and omnidirectional radiation patterns were obtained. It is suitable for application to a mobile phone with its relatively low profile. View full abstract»

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  • Multiband electromagnetic wave absorber based on reactive impedance ground planes

    Publication Year: 2010 , Page(s): 1720 - 1727
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    A novel structure able to perform multi-band absorption is presented. As is well known, the most famous and simplest radar absorbing material is the Salisbury screen. Improved solutions, aimed at a thickness reduction, have been presented in the literature, conceptually based on metamaterials and employing properly designed high-impedance surfaces (HIS) in practice. The absorber presented here combines the working principles of the previously mentioned designs in order to join the two types of absorber into a single structure. The novel design comprises a single resistive sheet mounted at a fixed distance from a reactive surface. The latter is a composite layer of a frequency selective surface printed on a grounded dielectric slab acting as an artificial magnetic conductor at lower frequencies, while responding as a perfect electric conductor at higher frequencies. The distance of the resistive sheet can therefore be dimensioned so as to recover the Salisbury functions in the upper band, while operating as a λ/10 absorber in the low-frequency regime. The structure is explained by means of a simple circuital model and measured data are reported to verify the proposed concepts. It is finally shown that low-frequency resonance can be advantageously adjusted by introducing some active elements in the HIS. View full abstract»

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  • Compact E-band planar quasi-Yagi antenna with folded dipole driver

    Publication Year: 2010 , Page(s): 1728 - 1734
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (977 KB)  

    A broadband planar quasi-Yagi antenna using a folded dipole driver is presented. The new antenna element is realised on a low dielectric constant substrate and it is suitable for millimetre-wave applications using low-cost thick-film fabrication. The advantage of the quasi-Yagi antenna with folded dipole driver compared to the standard quasi-Yagi antenna is a reduction in the length of the driver, which allows closer spacing of the elements for array applications on low dielectric constant substrates. Use of the folded dipole driver gives a 4:1 impedance range because of its extra parameters. The element was designed for E-band applications, but operates over a much wider bandwidth of approximately 1.3:1. Mutual coupling between two antenna elements in an array environment is investigated and results obtained are similar to conventional quasi-Yagi antenna elements. Four linear arrays, each containing four elements and having a different beamforming network, were fabricated to demonstrate the scanning capabilities of the folded dipole quasi-Yagi antenna, and measured reflection coefficient, radiation patterns and gain for each array are presented. View full abstract»

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  • Diversity performance of multiport dielectric resonator antennas

    Publication Year: 2010 , Page(s): 1735 - 1745
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    Single-structure dual and triple linearly polarised cylindrical dielectric resonator antennas (CDRAs) with respective excitation sets of two orthogonal modes and three degenerate modes at 120° to each other are investigated for operation as compact multiport antennas. The diversity performance of these multiport CDRAs is evaluated using theoretical expressions of envelope correlation coefficient, mean effective gain (MEG) and MEG ratio in conjunction with simulation and experimental S-parameter results. The multiport CDRAs portray low mutual coupling (<; -6.5 dB), different feed radiation pattern and polarisation directions, low envelope correlation coefficients (<;0.27) between feed points and near-equal branch MEG ratios (within ±1.8 dB). Thus, they satisfy the diversity performance benchmarks for application as compact multi-polarised diversity or multiple-input multiple-output antennas. View full abstract»

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  • Reconstruction of metal protrusion on flat ground plane

    Publication Year: 2010 , Page(s): 1746 - 1755
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (385 KB)  

    The authors present a gradient-based optimisation algorithm for the reconstruction of the shape of a metal protrusion on a flat ground plane based on the scattering matrix of an array antenna. The sensitivities are based on the continuum form of Maxwell's equations, which offers good flexibility with respect to the choice of field solver. The computational cost for the gradient is independent of the number of degrees of freedom that are used to represent the shape of the protrusion. Initial tests show that the sensitivities yield good accuracy in the 3D setting and that relatively good reconstructions of simple surfaces are feasible with a computational cost that amounts to about some ten evaluations of the scattering matrix. View full abstract»

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  • Dual-band microstrip antenna array with a combination of mushroom, modified Minkowski and Sierpinski electromagnetic band gap structures

    Publication Year: 2010 , Page(s): 1756 - 1763
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (895 KB)  

    A novel concept involving a single-port dual-band microstrip antenna array (DbMSAA) incorporated with electromagnetic band gap (EBG) structures is reported. Three types of EBG structures are used in the designs, which include the mushroom EBG, a modified Minkowski EBG and Sierpinski EBG structures. These EBG structures operate like a band rejecter, separating the branch of feed lines feeding two different groups of arrays of patch antennas, thus making them operate individually at their particular frequencies, simultaneously. Initially, with the new DbMSAA model configuration, the possibilities of having uniform and controlled radiation patterns are quite complicated to achieve because of the single-port feeding technique used and developments of grating lobes at the higher band frequency. By incorporating the EBG structures, these problems are solved. The antenna's performance improves with the radiation patterns of the dual-band antenna at both frequencies becoming more symmetrical and having increased gain. View full abstract»

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  • Comparison of frequency-selective screen-based linear to circular split-ring polarisation convertors

    Publication Year: 2010 , Page(s): 1764 - 1772
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1094 KB)  

    This study presents the use of periodic arrays of freestanding slot frequency-selective screens (FSS) as a means for generating circularly polarised signals from an incident linearly polarised signal at normal incidence to the structure. Measured and simulated results for crossed, linear and various ring slot element shapes in single and double-layer polarisation convertor structures are presented for 10 GHz operation. It is shown that 3 dB axial ratio (AR) bandwidths of 21% can be achieved with the one-layer perforated screen design and that the rate of change is lower than the double-layer structures. An insertion loss of 0.34 dB can be achieved for the split circular ring double-layer periodic array, and of the three topologies presented the hexagonal split-ring polarisation convertor gives the lowest variation of AR with angle of incidence 1.8 dB/45° and 3.6 dB/45° for the single and double-screen FSS, respectively. In addition, their tolerance to angle of incidence variation is presented. The capability of the surfaces reported here as twist polariser or spatial isolator components has been demonstrated with up to -30 dB isolation between incident and re-reflected signals for the double-layer designs being measured. View full abstract»

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  • Thru-less calibration algorithm and measurement system for on-wafer large-signal characterisation of microwave devices

    Publication Year: 2010 , Page(s): 1773 - 1781
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (441 KB)  

    A reflection-based thru-less de-embedding technique for voltage and current waveforms and absolute power flow measurements suitable for on-wafer large-signal characterisation of microwave transistors is proposed. Based on the novel calibration technique developed, which does not require any special `golden standard` for waveform calibration purposes, a comprehensive and relatively inexpensive power flow, impedance and waveform measurement system, using the microwave transition analyser as a two-channel receiver, is developed. The proposed calibration algorithm is fast, simple and accurate for power de-embedding and waveform measurements. This kind of on-wafer power de-embedding and waveform measurement is helpful in the design of switching-mode power amplifiers. The developed system was tested for both 50Ω and non-50Ω terminated passive and active devices, and the obtained results show very good agreement with those obtained with commercial instruments. View full abstract»

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  • Design and development of a conjugate matched feed for an offset parabolic reflector antenna

    Publication Year: 2010 , Page(s): 1782 - 1788
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (733 KB)  

    The design and development of a tri-mode conjugate matched feed, to suppress the unwanted high cross-polarisation and beam squinting in an offset parabolic reflector antenna, are presented. In a smooth-walled cylindrical waveguide, TE11, TM11 and TE21 modes are combined in proper amplitude and phase to configure a tri-mode conjugate matched feed. The performance of the proposed tri-mode horn was evaluated, and its simulated far-field radiation pattern is found to be in close agreement with the measured radiation pattern. This horn was then used as a primary feed device to illuminate the linearly polarised offset parabolic reflector antenna, and significant reduction in the cross-polarisation has been achieved in the secondary radiation pattern. Similarly, by illuminating the offset reflector with a circularly polarised matched feed, a squint-free radiation pattern has been achieved. View full abstract»

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  • Fully integrated 24 GHz differential active sub-harmonic mixer located in CMOS multi-layer Marchand baluns

    Publication Year: 2010 , Page(s): 1789 - 1798
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (753 KB)  

    A fully integrated active sub-harmonic mixer (SHM) located in two Marchand baluns is presented. The proposed circuit was designed at 24 GHz for industrial, scientific and medical (ISM) band applications and fabricated in a 0.13 μm complementary metal-oxide-semiconductor (CMOS) process. The proposed circuit layout is based on allocating the active SHM into square passive baluns to reduce the chip area without degrading performance. Two design approaches, one using a multi-layer and the other using compensated capacitors, were adopted in the CMOS Marchand baluns process to increase the coupling coefficient sufficiently and to minimise the required balun size. Additionally, the conversion gain was increased by using the current-bleeding scheme in the SHM. Moreover, a conversion gain of 3.8 dB was achieved in the designed circuit at a local oscillator (LO) input power of 5 dBm. Both radio frequency-intermediate frequency (IF) and LO-IF isolations were better than 28 dB. The proposed circuit not only has a higher conversion gain than other published mixers that are operated at millimetre-wave frequencies, but also has an innovative circuit layout. View full abstract»

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  • Construction of Green's functions of parallel plates with periodic texture with application to gap waveguides - a plane-wave spectral-domain approach

    Publication Year: 2010 , Page(s): 1799 - 1810
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    This study presents Green's functions of parallel-plate structures, where one plate has a smooth conducting surface and the other an artificial surface realised by a one-dimensional or two-dimensional periodic metamaterial-type texture. The purpose of the periodic texture is to provide cut-off of the lowest order parallel-plate modes, thereby forcing electromagnetic energy to follow conducting ridges or strips, that is, to form a gap waveguide as recently introduced. The Green's functions are constructed by using the appropriate homogenised ideal or asymptotic boundary conditions in the plane-wave spectral domain, thereby avoiding the complexity of the Floquet-mode expansions. In the special case of a single ridge or strip, an additional numerical search for propagation constants is needed and performed in order to satisfy the boundary condition on the considered ridge or strip in the spatial domain. The results reveal the dispersion characteristics of the quasi-transverse electromagnetic modes that propagate along the ridges or strips, including their lower and upper cut-off frequencies, as well as the theoretical decay of the modal field in the transverse cut-off direction. This lateral decay shows values of 50-100 dB per wavelength for realisable geometries, indicating that the gap waveguide modes are extremely confined. The analytical formulas for the location of the stopband of the lowest order parallel-plate modes obtained by small-argument approximation of the dispersion equation are also shown. To verify the proposed analysis approach, the results are compared with the results obtained with a general electromagnetic solver showing very good agreement. View full abstract»

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  • Compact ultra-wideband slot antenna fed by coplanar waveguide and microstrip line with triple-band-notched frequency function

    Publication Year: 2010 , Page(s): 1811 - 1817
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (901 KB)  

    A compact ultra-wideband (UWB) printed slot antenna fed by coplanar waveguide (CPW) and microstrip line with multi-band-rejection characteristics is proposed. The small antenna fed by CPW and microstrip line has a volume of 40 × 22 × 0.8 × mm3. By adding an inverted U-shape slot on the tapered radiating patch, the antenna provides band-rejection characteristics. The centre frequencies of three notched bands at 2.4, 3.5 and 5.5 GHz can be adjusted by modifying the length of the inserted slot. Good agreement is achieved between the simulated and measured results. The measured impedance bandwidth of the proposed antenna ranges from 2 to 12 GHz for voltage standing wave ratio ≤ 2, excluding the rejection bands. The omni-directional radiation patterns of the fabricated antenna fed by CPW and microstrip line are presented, which show that the designed antenna is a good candidate for various UWB applications. The measured peak gain variation is less than 4 dB over the operating frequency band. View full abstract»

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  • Experimental approach for robust identification of radiofrequency power amplifier behavioural models using polynomial structures

    Publication Year: 2010 , Page(s): 1818 - 1828
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1013 KB)  

    Here, the robustness of polynomial model identification for radiofrequency power amplifiers (PAs) driven by wideband code division multiple access (WCDMA) signals is investigated. The ill-conditioning problem is highlighted, and the sensitivity of the model identification to disturbance is demonstrated. These issues are mainly related to the correlated character of the WCDMA signal. The identification robustness is then enhanced using, instead of the WCDMA input, a synthetic wideband signal with a parametrised probability density function (pdf) close to that of the WCDMA signal, which is of the Rayleigh type. The pdf of the synthetic signal is chosen in order to have the best conditioning values. The signal characteristics, including bandwidth and average power, are controlled to maintain the same amplifier average operating conditions during the characterisation step. Measurement results performed on a 300 W Doherty PA illustrate satisfactory modelling accuracy and significant improvement in the identification robustness achieved by using the proposed approach. View full abstract»

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  • Near-field to far-field transformation utilising multilevel plane wave representation for planar and quasi-planar measurement contours

    Publication Year: 2010 , Page(s): 1829 - 1837
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (566 KB)  

    A fully probe-corrected near-field far-field transformation employing plane wave expansion and diagonal translation operators has recently been presented, which is able to efficiently carry out transformations for arbitrary measurement point locations. Here, the algorithm is discussed in its multilevel version for the application to planar and quasi-planar measurement contours. The measurement points are grouped in a multilevel box structure and translations of the plane waves, representing the antenna under test, are only carried out to the box centres on the highest level. The plane waves are further processed through the different levels towards the measurement points with a decreasing sampling rate using a disaggregation and anterpolation procedure. This reduces the overall complexity to O(N q log N), N being the total number of measurement points, which is comparable to the classical fast Fourier transform-based algorithms for planar measurements. The proposed algorithm includes a full correction of arbitrary near-field probes and is able to cope with irregular measurement grids and is further optimised for highly directive antennas within this contribution. View full abstract»

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  • Near-field radiation characteristics of shaped electrically large apertures in the spatial and angular domains

    Publication Year: 2010 , Page(s): 1838 - 1846
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (634 KB)  

    According to the equivalence principle, the aperture near-field can be expressed as the convolution of the aperture field and the spatial network response function. Therefore the aperture near-field angular spectrum can be expressed as the product of the angular-domain spectrum of the aperture field and the angular-domain spectrum of the spatial network response function. The spatial network function acts as an angular spectrum filter. Based on the aperture field convolution method, the near-field radiation of several electrically large apertures has been computed and compared in the spatial and angular domains, including a circular aperture, a square aperture and a well-designed serrated edge aperture. The following facts have been demonstrated by the numerical results: The serrated edge aperture has the most uniform near-field amplitude and phase distribution, both in the transverse plane and in the central axis. The plane-wave spectrum components received by a certain observation plane are related to its position, size and shape. The direct wave and edge diffraction waves can be observed qualitatively and quantitatively in the angular domain. The edge diffraction waves cannot be distinguished when the transverse size of the observation plane is less than a certain value. Finally, based on general rules of compact antenna test range design, the angular-domain analysis applications for the evaluation of the aperture shape design and the diagnosis of the aperture deformation are presented. All the three aperture diameters are limited to 150 wavelengths in free space. Inverse Fourier transform with a Hamming window has been adopted for the spatial-angular transform. View full abstract»

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  • Ring-balun-bandpass filter with harmonic suppression

    Publication Year: 2010 , Page(s): 1847 - 1854
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (615 KB)  

    The Y-matrix of a three-port dual-mode ring resonator for a balun-bandpass filter (BPF) application is derived. Using Y parameters, it is verified that the structure theoretically satisfies the general balun conditions. The admittance slope parameters of the dual-mode ring resonator with one terminated port are derived so that one can design balun-BPFs using the conventional standard BPF design procedure. The proposed equations are validated by designing a balun-BPF. Inverters are then substituted with low-pass filter unit cells of λ/4 electrical length to suppress harmonics from the second to the fourth. The experimental measurements show good agreement with theoretical and electromagnetic-simulated predictions and suppressed harmonics below λ30λdB up to fourth-order harmonics. View full abstract»

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  • Perfect plane wave injection for Crank-Nicholson time-domain method

    Publication Year: 2010 , Page(s): 1855 - 1862
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (403 KB)  

    The authors derive a 1D multipoint auxiliary source propagator for perfect plane wave injection (PWI) with the Crank-Nicholson time-domain scheme for the first time. By projecting the 2D dispersion equation onto the 1D case, the identical dispersion relation can be realised between the 1D case and the 2D case, which leads to a perfect PWI at any angle forming an integer grid cell ratio. Several numerical experiments are conducted, which show leakage errors on the order of finite precision (-300-dB for double precision) when -t is around the Courant-Friedrichs-Levy (CFL) limit. Beyond the CFL limit, the leakage error is still kept low even though it deteriorates with increasing time-step increments. Good agreement is observed between the proposed method and analytic solution for scattering of a 2D perfect electric conductor circular scatterer. View full abstract»

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  • Modelling perfect electric conductor thin-wires that penetrate finite-size dielectric interfaces

    Publication Year: 2010 , Page(s): 1863 - 1869
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    The modelling of finite-size dielectric (and/or magnetic) material via surface integral equation (SIE) formulations and the method of moments (MoM) in the resonance region is dominated by a triangular-mesh description of the surfaces and supported by Rao-Wilton-Glisson basis functions. Previous formulations allow perfect electric conductor (PEC) thin-wires to be included in the modelling domain when the wires are external or internal to the dielectric surfaces. This study discusses the adjustments to be made in an SIE formulation and MoM to enable the modelling of PEC thin-wires that penetrate one or more dielectric surfaces of finite size and shows that the results are in excellent agreement with the other methods. View full abstract»

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  • Several theorems for reflection and transmission coefficients of plane wave incidence on planar multilayer metamaterial structures

    Publication Year: 2010 , Page(s): 1870 - 1879
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    Consider an arbitrarily polarised plane wave obliquely incident on a planar multilayer structure composed of a combination of natural materials and metamaterials, then the following three new theorems are proved in this paper. Theorem 1: Consider a planar multilayer structure made of a combination of common materials and metamaterials situated between two half spaces composed of lossless media. Now each layer is filled by its dual media according to the interchanges DPS ↔ DNG and ENG ↔ MNG. Then, the reflection (R) and transmission (T) coefficients from the structure become the complex conjugates of their counterparts. Consequently, the reflected power and transmitted power from the structure are the same for the two dual cases. Theorem 2: If the interchanges DPS ↔ DNG and ENG ↔ MNG are made in all the layers except in the half spaces on the two sides of the multilayer structure, then the reflection coefficients become complex conjugates and the reflected power remains the same. Theorem 3: If a planar multilayer structure is backed by a perfect electric conductor and the media interchanges DPS ↔ DNG and ENG ↔ MNG are made in the layers, then the reflection coefficients of the two dual structures become complex conjugates of each other, and the reflected powers are equal. Finally, several examples and applications with dispersion are included. View full abstract»

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  • Internal mirrors for time-reversal optimisation

    Publication Year: 2010 , Page(s): 1880 - 1885
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (302 KB)  

    This study reports on the use of time-reversal techniques for the design and optimisation of microwave components. Loss of spatial resolution due to evanescent mode decay in the presence of finite machine precision restricts the scope for optimising large complex devices. This serious problem is addressed by introducing internal time-reversal mirrors for the first time. In conjunction with an explicit local modal decomposition, these mirrors ensure that the evanescent fields scattered from a component are correctly captured. Although equally applicable to any time-domain simulation technique, in this work the transmission-line modelling method is used to implement the necessary forward and reverse-time simulations. View full abstract»

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  • Improved band-notch technique for ultra-wideband antenna

    Publication Year: 2010 , Page(s): 1886 - 1891
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    This study describes a compact ultra-wideband (UWB) antenna that exhibits desirable band-notch and gain characteristics. The antenna consists of a rectangular aperture etched on a printed circuit board's ground plane that is excited by a taper shaped patch. The antenna's broadband matching impedance is enhanced by inserting periodic open-end stubs (POES) on the inside edge of the rectangular aperture. A band-notch function to eliminate the WLAN interfering signals between 5 and 6'GHz is created on the proposed antenna using three different techniques. It is shown that the frequency of the band-notch characteristic can be tuned by varying the parameters of the notching structure. The antenna was fabricated and its performance measured to validate its feasibility and the band-notch techniques. A compact aperture area of 12'23'mm2 is realised which exhibits an excellent voltage standing wave ratio (VSWR) performance and stable radiation patterns over the UWB spectrum. View full abstract»

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  • Rapid design optimisation of microwave structures through automated tuning space mapping

    Publication Year: 2010 , Page(s): 1892 - 1902
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1171 KB)  

    Tuning space mapping (TSM) is one of the latest developments in space mapping technology. TSM algorithms offer a remarkably fast design optimisation with satisfactory results obtained after one or two iterations, which amounts to just a few electromagnetic simulations of the optimised microwave structure. The TSM algorithms (as exemplified by `Type-1` tuning) could be simply implemented manually. The approach may require interaction between various electromagnetic-based and circuit models, as well as handling different sets of design variables and control parameters. As a result, certain TSM algorithms (especially so-called `Type-0` tuning) may be tedious, thus, error-prone to implement. Here, we present a fully automated tuning space mapping implementation that exploits the functionality of our user-friendly space mapping software, the SMF system. The operation and performance of our new implementation is illustrated through the design of a box-section Chebyshev bandpass filter and a capacitively coupled dual-behaviour resonator filter. View full abstract»

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