ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 02 Jul 2020 10:32:40 GMT2020-07-02T10:32:40Z503721- Dominant lateral waves in the canopy layer of a four-layered foresthttps://scholarbank.nus.edu.sg/handle/10635/62061Title: Dominant lateral waves in the canopy layer of a four-layered forest
Authors: Koh, J.H.; Li, L.W.; Kooi, P.S.; Yeo, T.S.; Leong, M.S.
Abstract: In this paper a forest model of four-layered geometry is utilized for the theoretical analysis of radio wave propagation characteristics in the forest environment. Differing from those reported in previous publications, the current paper considers a receiving antenna that is located in the forest canopy layer instead of the trunk layer, and hence the results presented are not available elsewhere. Dyadic Green's functions in their eigenfunction expansion forms for the four-layered geometry are used at first to obtain an exact integral representation of the radiated electric field in the canopy layer. The radiated electric field components due to an arbitrarily oriented, small dipole in the trunk layer are then evaluated using the saddle point technique and the branch cut integrations, leading to closed-form expressions for the field. The total field is found to consist of the direct, the reflected, and the lateral waves. Although both the lateral waves propagating along the air-canopy and the trunk-ground interfaces play an important role in the propagation mechanism, only the lateral wave along the air-canopy upper interface dominates the total field in the far zone. Path loss of the radio waves in the forest is computed numerically for both the vertically and the horizontally oriented dipoles.
Sat, 01 May 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/620611999-05-01T00:00:00Z
- Efficient analysis of electromagnetic scattering and radiation from patches on finite, arbitrarily curved, grounded substrateshttps://scholarbank.nus.edu.sg/handle/10635/82241Title: Efficient analysis of electromagnetic scattering and radiation from patches on finite, arbitrarily curved, grounded substrates
Authors: Yuan, N.; Yeo, T.S.; Nie, X.C.; Li, L.W.; Gan, Y.B.
Abstract: A precorrected-fast Fourier transform (FFT) accelerated surface integral equation approach formulated using the homogeneous medium Green's function is presented for the analysis of patch arrays on finite, arbitrarily shaped, grounded substrate. The integral equation is solved by the method of moments, and the precorrected-FFT method is applied to reduce the memory requirement and computational complexity of the solution procedure. The memory required for this algorithm is O(N1.5), and the computational complexity is N iterW1.5log N, where N is the number of unknowns and Niter is the iteration number. Numerical results are presented to demonstrate the accuracy and capability of the method.
Sat, 01 May 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/822412004-05-01T00:00:00Z
- Stacked phased array coils for increasing the signal-to-noise ratio in magnetic resonance imaginghttps://scholarbank.nus.edu.sg/handle/10635/57513Title: Stacked phased array coils for increasing the signal-to-noise ratio in magnetic resonance imaging
Authors: Liang, D.; Hui, H.T.; Yeo, T.S.; Li, B.K.
Abstract: A new concept of using a stacked phased coil array to increase the signal-to-circuit noise ratio (SCNR) in magnetic resonance imaging (MRI) is introduced. Unlike conventional phased coil arrays, the proposed stacked phased coil array is constructed by stacking the coil elements closely together in the vertical direction. Through a proper combination of the coil terminal voltages, the SCNR is shown to increase with the square root of the number of coil elements. A prototype two-element array is constructed and an experimental method is designed to determine the combiner coefficients in a simulated MRI electromagnetic field environment. The experimental results show that the mutual coupling effect among the array coils can be totally removed and the combiner output voltage increases with the number of coil elements. This demonstrates the feasibility of the proposed method. © 2012 IEEE.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/575132013-01-01T00:00:00Z
- A Method for Designing Broad-Band Microstrip Antennas in Multilayered Planar Structureshttps://scholarbank.nus.edu.sg/handle/10635/54353Title: A Method for Designing Broad-Band Microstrip Antennas in Multilayered Planar Structures
Authors: Liu, Z.-F.; Kooi, P.-S.; Li, L.-W.; Leong, M.-S.; Yeo, T.-S.
Abstract: The narrow bandwidth of a microstrip antenna is one of the important features that restrict its wide usage. A simple and practical method for the design of broad-band microstrip antennas is presented in this paper. Utilizing this design technique, several two-layer microstrip antennas have been proposed. To confirm the applicability of the method for the designs of antennas at L-band, experiments have been carried out. The measured results show that the proposed antennas have a bandwidth of up to 25.7%. Also, the method proposed in this paper is applicable to the design of other types of multilayered planar antennas. © 1999 IEEE.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/543531999-01-01T00:00:00Z
- Radiation of an aperture antenna covered by a spherical-shell chiral radome and fed by a circular waveguidehttps://scholarbank.nus.edu.sg/handle/10635/81041Title: Radiation of an aperture antenna covered by a spherical-shell chiral radome and fed by a circular waveguide
Authors: Li, L.-W.; Leong, M.-S.; Kooi, P.-S.; Yeo, T.-S.; Qiu, Y.-L.
Abstract: This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TEi i mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically. © 1998 IEEE.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/810411998-01-01T00:00:00Z
- Integrated multibeam dual-polarised planar arrayhttps://scholarbank.nus.edu.sg/handle/10635/56349Title: Integrated multibeam dual-polarised planar array
Authors: Gao, S.-C.; Li, L.-W.; Leong, M.-S.; Yeo, T.-S.
Abstract: A novel four-beam dual-polarised microstrip antenna array at the 10GHz band is presented. By using a multilayered structure and multiport slot-coupled microstrip lines, two Butler matrix microstrip circuits corresponding to two orthogonal polarisations can be located on different substrate layers (above and below the ground plane) and integrated with a patch array. The antenna has eight input ports corresponding to two orthogonal polarisations and four beams. The theoretical design is based on the finite-difference time-domain (FDTD) method. The measured return loss and isolation characteristics exceed 10 and 23dB, respectively, in the 9.7-10.3GHz band. The radiation pattern is close to an ideal Butler pattern and the cross-polarisation level is lower than -18dB in the beams. Details of the antenna and its characteristics are presented.
Fri, 01 Jun 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/563492001-06-01T00:00:00Z
- Analysis of hollow conducting waveguides using superquadric functions-a unified representationhttps://scholarbank.nus.edu.sg/handle/10635/61829Title: Analysis of hollow conducting waveguides using superquadric functions-a unified representation
Authors: Lin, S.-L.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: Waveguides of various geometries have found many applications. The analysis of the wave modes inside these waveguides are usually subject to cross sections of the waveguides and specific, but convenient, coordinates systems have to be chosen in the analysis. In this paper, the boundary geometries of waveguides (which include rectangular, circular, elliptical, triangular, coaxial, etc.) are represented in a unified manner by a superquadric function. In this paper, with the Rayleigh-Ritz method, the wave propagation characteristics in a hollow conducting waveguide of the superquadric cross section are analyzed in a unified manner. From the analysis, it is realized that the superquadric function can be utilized to accurately model the boundary of various waveguide structures through variation of the shape parameters. The comparisons between the analytical and computational results show this method is accurate and efficient. © 2000 IEEE.
Mon, 01 May 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/618292000-05-01T00:00:00Z
- Three-dimensional SAR imaging of a ground moving target using the InISAR techniquehttps://scholarbank.nus.edu.sg/handle/10635/57664Title: Three-dimensional SAR imaging of a ground moving target using the InISAR technique
Authors: Zhang, Q.; Yeo, T.S.
Abstract: In this paper, a three-dimensional (3-D) interferometric synthetic aperture radar (ISAR) imaging method for moving targets is presented. This imaging method is based on the ISAR principle and the simple observation that all scatterers on a moving target move in tandem. The angular motion parameters in the cross-range directions could be estimated using the overall range profile of the moving target. Registration of the respective complex images at the two (or more) interferometric antennas can then be achieved via compensating the respective echoes at the raw data level, thus avoiding phase-unwrapping processing and image-resampling processing as required by conventional methods. Finally, a 3-D image of the moving target can then be reconstructed from the 3-D spatial coordinates of these scatterers. Furthermore, the method works well even for a target moving in heavily cluttered environments.
Wed, 01 Sep 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576642004-09-01T00:00:00Z
- Imaging of a moving target with rotating parts based on the hough transformhttps://scholarbank.nus.edu.sg/handle/10635/56253Title: Imaging of a moving target with rotating parts based on the hough transform
Authors: Zhang, Q.; Yeo, T.S.; Tan, H.S.; Luo, Y.
Abstract: The rotation of structures in a target introduces additional frequency modulations on the returned signals and also generates sidebands about the center Doppler frequency of the target. In other words, the body image will be contaminated due to the interference from the rotating parts. In this paper, an imaging method for moving targets with rotating parts is presented. The method is simple to implement and is based on the Hough transform (HT), which is widely used in image processing. Using the standard HT and an extended HT, we put forward a separation method by detecting the straight lines and the sinusoids on the spectrogram, respectively. A computer simulation is given to illustrate the effectiveness of the proposed method. © 2007 IEEE.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/562532008-01-01T00:00:00Z
- Three-dimensional imaging using colocated MIMO radar and ISAR techniquehttps://scholarbank.nus.edu.sg/handle/10635/57659Title: Three-dimensional imaging using colocated MIMO radar and ISAR technique
Authors: Ma, C.; Yeo, T.S.; Tan, C.S.; Li, J.-Y.; Shang, Y.
Abstract: A conventional inverse synthetic aperture radar image is a 2-D range-Doppler projection of a target and does not provide 3-D information. Three-dimensional imaging using an interferometric technique cannot separate scatterers that have been projected onto the same range-Doppler unit. Multiple-input-multiple-output (MIMO) radar, however, in addition to having a wide virtual aperture and a high cross-range resolution, could also obtain a target's 3-D image in one snapshot. We discuss in this paper the use of time-domain information to improve MIMO radar's imaging quality. A 3-D image alignment algorithm and a rotation vector estimation method are discussed. Simulation results show that image SNR is improved and cross-range sidelobes are mitigated. © 2012 IEEE.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576592012-01-01T00:00:00Z
- Bistatic ISAR imaging incorporating interferometric 3-D imaging techniquehttps://scholarbank.nus.edu.sg/handle/10635/55209Title: Bistatic ISAR imaging incorporating interferometric 3-D imaging technique
Authors: Ma, C.; Yeo, T.S.; Guo, Q.; Wei, P.
Abstract: Bistatic inverse synthetic aperture radar (BiISAR) imaging provides complementary information to monostatic ISAR imaging. A suggestion that the conventional bistatic ISAR can be replaced by an equivalent monostatic radar is shown to be inadequate in this paper. We prove that the BiISAR image is a sheared version of the projection of the target on the range-Doppler plane. A bistatic interferometric radar configuration is proposed to correct this distortion and to form 3-D image. Simulation results have validated our analysis and shown the viability of the proposed 3-D imaging algorithm. © 1980-2012 IEEE.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/552092012-01-01T00:00:00Z
- Indirect modelling of the scattering from two-dimensional composite uniaxial bianisotropic cylinders of arbitrary cross-sectionshttps://scholarbank.nus.edu.sg/handle/10635/56318Title: Indirect modelling of the scattering from two-dimensional composite uniaxial bianisotropic cylinders of arbitrary cross-sections
Authors: Yin, W.-Y.; Li, L.-W.; Leong, M.-S.; Yeo, T.-S.
Abstract: The indirect modelling of electromagnetic scattering from two-dimensional composite uniaxial bianisotropic cylinders of arbitrary cross-section is successfully performed according to the principle of equivolumetric model. The mathematical treatment here is based on the generalized boundary-value method combined with the technique of separate variables. The solution is obtained from a system of linear equations of infinite order which is then truncated during numerical computations. Then, numerical investigation is carried out to demonstrate hybrid effects of geometrical and constitutive parameters of guest and host cylinders on the co- and cross-polarized echo widths in the far-field zone. It is shown that under certain circumstances, the indirect modelling technique is very efficient to study the scattering characteristics of many practical complex planar structures, and has some advantages over the direct numerical method.
Tue, 01 May 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/563182001-05-01T00:00:00Z
- Improved signal-to-noise ratio performance in magnetic resonance imaging by using a multilayered surface coil array - A simulation studyhttps://scholarbank.nus.edu.sg/handle/10635/56282Title: Improved signal-to-noise ratio performance in magnetic resonance imaging by using a multilayered surface coil array - A simulation study
Authors: Liang, D.; Hui, H.T.; Yeo, T.S.
Abstract: A multilayered surface coil array for magnetic resonance imaging with an improved signal-to-noise ratio (SNR) performance is introduced and investigated by a simulation study. By using an effective decoupling method, the strong mutual coupling effect between the coil layers can be accurately removed, leading to a coherent combination of the signals of the individual coils. This results in a much stronger received signal power which increases with the number of coil layers in the array. This, together with a smaller rate of increase of noise power with the number of coil layers, leads to a net increase in the SNR of array output with the number of coil layers in the array. Rigorous numerical simulation examples have been carried out to confirm and verify the performance of the new array.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/562822013-01-01T00:00:00Z
- Corrections to "a fast analysis of scattering and radiation of large microstrip antenna arrays"https://scholarbank.nus.edu.sg/handle/10635/67881Title: Corrections to "a fast analysis of scattering and radiation of large microstrip antenna arrays"
Authors: Yuan, N.; Yeo, T.S.; Nie, X.C.; Li, L.W.
Thu, 01 Jan 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/678812004-01-01T00:00:00Z
- A fast volume-surface integral equation solver for scattering from composite conducting-dielectric objectshttps://scholarbank.nus.edu.sg/handle/10635/54139Title: A fast volume-surface integral equation solver for scattering from composite conducting-dielectric objects
Authors: Nie, X.-C.; Yuan, N.; Li, L.-W.; Gan, Y.-B.; Yeo, T.S.
Abstract: This paper presents a fast hybrid volume-surface integral equation approach for the computation of electromagnetic scattering from objects comprising both conductors and dielectric materials. The volume electric field integral equation is applied to the material region and the surface electric field integral equation is applied on the conducting surface. The method of moments (MoM) is used to convert the integral equation into a matrix equation and the precorrected-FFT (P-FFT) method is employed to reduce the memory requirement and CPU time for the matrix solution. The present approach is sufficiently versatile in handling problems with either open or closed conductors, and dielectric materials of arbitrary inhomogeneity, due to the combination of the surface and volume electric field integral equations. The application of the precorrected-FFT method facilitates the solving of much larger problems than can be handled by the conventional MoM. © 2005 IEEE.
Tue, 01 Feb 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/541392005-02-01T00:00:00Z
- Cylindrical vector wave function representation of Green's dyadics for uniaxial bianisotropic mediahttps://scholarbank.nus.edu.sg/handle/10635/55493Title: Cylindrical vector wave function representation of Green's dyadics for uniaxial bianisotropic media
Authors: Li, L.-W.; Lim, N.-H.; Leong, M.-S.; Yeo, T.-S.; Jin Au Kong
Abstract: This paper presents a novel and rigorous eigenfunction expansion of electric-type dyadic Green's function for an unbounded uniaxial bianisotropic medium in terms of the cylindrical vector wave functions. The Green's dyadic is obtained on the basis of the well-known Ohm-Rayleigh method together with some newly developed vector and tensor identities formed by the differential, curl, and dot product of the constitutive dyadics and the cylindrical vector wave functions. The above identities greatly simplify the process of finding the vector expansion coefficients of the dyadic Green's function of the uniaxial bianisotropic media. The dyadic Green's function derived is expressed in terms of the contribution from the irrotational solenoidal types of vector wave functions, with the λ integrals removed using the residue theorem.
Sun, 01 Jul 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/554932001-07-01T00:00:00Z
- Scattering by rotationally symmetric anisotropic spheres: Potential formulation and parametric studieshttps://scholarbank.nus.edu.sg/handle/10635/57335Title: Scattering by rotationally symmetric anisotropic spheres: Potential formulation and parametric studies
Authors: Qiu, C.-W.; Li, L.-W.; Yeo, T.-S.; Zouhdi, S.
Abstract: Vector potential formulation and parametric studies of electromagnetic scattering problems of a sphere characterized by the rotationally symmetric anisotropy are studied. Both ̄ and μ̄ tensors are considered herein, and four elementary parameters are utilized to specify the material properties in the structure. The field representations can be obtained in terms of two potentials, and both TE (TM) modes (with respect to r) inside (outside) the sphere can be derived and expressed in terms of a series of fractional-order (in a real or complex number) Ricatti-Bessel functions. The effects due to either electric anisotropy ratio (Ae = t r) or magnetic anisotropy ratio (Am = μt μr) on the radar cross section (RCS) are considered, and the hybrid effects due to both Ae and Am are also examined extensively. It is found that the material anisotropy affects significantly the scattering behaviors of three-dimensional dielectric objects. For absorbing spheres, however, the Ae or Am no longer plays a significant role as in lossless dielectric spheres and the anisotropic dependence of RCS values is found to be predictable. The hybrid effects of Ae and Am are considered for absorbing spheres as well, but it is found that the RCS can be greatly reduced by controlling the material parameters. Details of the theoretical treatment and numerical results are presented. © 2007 The American Physical Society.
Tue, 13 Feb 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/573352007-02-13T00:00:00Z
- Motion parameter estimation in the SAR system with low PRF samplinghttps://scholarbank.nus.edu.sg/handle/10635/56697Title: Motion parameter estimation in the SAR system with low PRF sampling
Authors: Wu, Q.; Xing, M.; Qiu, C.; Liu, B.; Bao, Z.; Yeo, T.-S.
Abstract: A novel approach to motion parameter estimation with low pulse repetition frequency (PRF) sampling based on compressed sensing (CS) theory is introduced. As is known to us, when PRF is less than the Doppler spectrum bandwidth, moving targets suffer both Doppler centroid frequency ambiguity and Doppler spectrum ambiguity. Under this condition, the traditional parameter estimation method in the Doppler domain is out of action. The key of this letter converts motion parameter estimation in the synthetic aperture radar system with low PRF sampling into solving an optimization equation based on CS theory. Because moving targets in the scene can be regarded as sparse signals after clutter cancellation, an optimization algorithm based on CS theory is proposed to reconstruct sparse signals and meanwhile estimate the along-track velocities and azimuth positions of moving targets. Considering the fact that range cell migration of moving targets is not subject to PRF limitations, Radon transform is adopted to obtain unambiguous across-track velocities and range positions. Results on simulation and real data are provided to show the effectiveness of this method. © 2010 IEEE.
Thu, 01 Jul 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/566972010-07-01T00:00:00Z
- Cylindrical vector eigenfunction expansion of Green dyadics for multilayered anisotropic media and its application to four-layered foresthttps://scholarbank.nus.edu.sg/handle/10635/55491Title: Cylindrical vector eigenfunction expansion of Green dyadics for multilayered anisotropic media and its application to four-layered forest
Authors: Li, L.-W.; Koh, J.-H.; Yeo, T.-S.; Leong, M.-S.; Kooi, P.-S.
Abstract: A complete eigenfunction expansion of the dyadic Green's functions (DGFs) for planar, arbitrary multilayered anisotropic media using cylindrical vector wave functions is presented. These formulations are constructed based on the principle of scattering superposition. For the scattering dyadic Green's function in each layer, the scattering coefficients of TE and TM modes are determined from the boundary conditions matched at the planar interfaces. The explicit representation of the DGFs after reduction to the isotropic case agrees well with the existing results corresponding to the isotropic media. The general DGFs for multilayered anisotropic media are then reduced to those for a four-layered forest where the trunk layer is modeled as anisotropic medium. Application is further made for radio-wave propagation through forests of a four-layered geometry, whereas it is shown how these Green dyadic formulations are used in a practical way and how the field distributions due to a dipole can be obtained.
Sun, 01 Feb 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/554912004-02-01T00:00:00Z
- Three-dimensional imaging of targets using colocated MIMO radarhttps://scholarbank.nus.edu.sg/handle/10635/57658Title: Three-dimensional imaging of targets using colocated MIMO radar
Authors: Ma, C.; Yeo, T.S.; Tan, C.S.; Liu, Z.
Abstract: Conventional inverse synthetic aperture radar image is a 2-D range-Doppler projection of a target and does not provide 3-D information. Its formation also requires complex motion compensation when the target is uncooperative and maneuvering. On the other hand, multiple-input and multiple-output (MIMO) radar, in addition to having a wide virtual aperture and high cross-range resolution, could also obtain a target's 3-D image in one snapshot and thus have avoided the complex motion compensation needed. In this paper, we propose a 3-D imaging algorithm using three MIMO configurations. The signal model is derived based on a modified zero correlation zone code. A strong scatterer selection criterion is also proposed for the construction of the target profile. © 2011 IEEE.
Mon, 01 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576582011-08-01T00:00:00Z
- Analysis of scattering from composite conducting and dielectric targets using the precorrected-FFT algorithmhttps://scholarbank.nus.edu.sg/handle/10635/68126Title: Analysis of scattering from composite conducting and dielectric targets using the precorrected-FFT algorithm
Authors: Yuan, N.; Yeo, T.S.; Nie, X.C.; Li, L.W.; Gan, Y.B.
Abstract: A precorrected-FFT algorithm is presented for the calculation of electromagnetic scattering from conducting objects coated with lossy materials. The problem is formulated using an EFIE-PMCHW formulation, which employs the electric field integral equation (EFIE) for conducting objects and the PMCHW formulation for dielectric objects. The integral equations are then discretized by the method of moments (MoM). in which the conducting and dielectric surfaces are represented by triangular patches and the unknown equivalent electric and magnetic currents are expanded using the RWG basis functions. The resultant matrix equation is solved iteratively and the precorrected-FFT method is used to speed up the matrix-vector products in iterations as well as to reduce the memory requirement. Numerical examples are presented to validate the implementation and to demonstrate the accuracy of the method.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/681262003-01-01T00:00:00Z
- Novel unified mode matching analysis of concentric waveguide junctionshttps://scholarbank.nus.edu.sg/handle/10635/56842Title: Novel unified mode matching analysis of concentric waveguide junctions
Authors: Lin, S.L.; Li, L.W.; Yeo, T.S.; Leong, M.S.
Abstract: A novel unified mode matching technique is proposed for the calculation of the modal scattering matrix of concentric waveguide junctions. The TE and TM modal fields in both waveguides which are connected to form the junction are expressed in the Cartesian coordinate system, so that the coupling coefficients of all the modes can be evaluated effectively. All types of waveguide junction are dealt with in a similar manner and no special function is required. As examples, scattering parameters of nine types of waveguide junction are calculated and compared with other methods or measurements in the literature. Very good agreement in all these cases demonstrates the efficiency, accuracy and flexibility of this technique.
Sat, 01 Dec 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/568422001-12-01T00:00:00Z
- Field representations in general gyrotropic media in spherical coordinateshttps://scholarbank.nus.edu.sg/handle/10635/56055Title: Field representations in general gyrotropic media in spherical coordinates
Authors: Qiu, C.-W.; Li, L.-W.; Wu, Q.; Yeo, T.-S.
Abstract: This letter presents a field expansion of the solution to three-dimensional electromagnetic problems in a material characterized by the general gyrotropic media. Both ε̄ and μ̄ tensors are gyrotropic, specified by six components and considered in the present analysis under spherial coordinates. Electromagnetic fields in general gyrotropic media are solved by using the method of separation of variables. Much effort is paid to the solution of a coupled set of second-order differential equations. Some specific situations of the parameters are investigated in detail. By properly grouping some terms, the electromagnetic fields are represented in a compact form. Compared to the existing results in the spherical coordinate system, the material properties investigated in this letter are more general. The general expressions of the fields are found to be reducible to those existing results for simplier cases. © 2005 IEEE.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/560552005-01-01T00:00:00Z
- Wave mode and path characteristics in a four-layered anisotropic forest environmenthttps://scholarbank.nus.edu.sg/handle/10635/57794Title: Wave mode and path characteristics in a four-layered anisotropic forest environment
Authors: Li, L.-W.; Lee, C.-K.; Yeo, T.-S.; Leong, M.-S.
Abstract: A four-layered forest geometry with two anisotropic slabs representing canopy and trunk is used for the investigation of wave characteristics in forest environment. Propagation of radio waves is examined in which the transmitter is embedded inside the forest, while the receiving point is located either inside the forest or above the vegetation. Dyadic Green's functions in their eigen-function expansion forms for planarly layered anisotropic media are applied to analyze this problem. The analytical close forms of these electric fields are then obtained by using the saddle point techniques, and branch cut integrations in the complex plane and, hence, expressed in terms of quasidirect wave, multiply reflected waves, and lateral waves. Propagation mechanisms of these waves are studied and radio losses in a typical forest are calculated numerically. © 2004 IEEE.
Wed, 01 Sep 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/577942004-09-01T00:00:00Z
- Electromagnetic Dyadic green's functions for multilayered spheroidal structures - I: Formulationhttps://scholarbank.nus.edu.sg/handle/10635/50553Title: Electromagnetic Dyadic green's functions for multilayered spheroidal structures - I: Formulation
Authors: Li, L.-W.; Kang, X.-K.; Leong, M.-S.; Kooi, P.-S.; Yeo, T.-S.
Abstract: Dyadic Green's functions (DGFs) and their scattering coefficients are formulated in this paper for defining the electromagnetic fields in multilayered spheroidal structures. The principle of scattering superposition is applied. In a similar form of the DGF in an unbounded medium under spheroidal coordinates, the scattering DGFs due to multiple spheroidal interfaces are expanded in terms of the spheroidal vector wave functions. For the lack of general orthogonality of the spheroidal radial and angular functions, the Green's dyadics are expressed in a different way where the coordinate unit vectors are also combined in the construction, as compared with the conventional form of vector wave eigenfunction expansion. The matrix equation systems satisfied by the coupled scattering (i.e., reflection and transmission) coefficients of the DGFs are obtained so that these coefficients can be solved uniquely. The DGFs can be employed to investigate effects of spheroidal radomes used to protect the air-borne or satellite antenna systems and of handy phone radiation near the spheroid-shaped human head, and so forth. Numerical calculations about the applications of the formulated multilayered DGFs will he presented in part II of this paper.
Thu, 01 Mar 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/505532001-03-01T00:00:00Z
- A broadband and high-gain metamaterial microstrip antennahttps://scholarbank.nus.edu.sg/handle/10635/53916Title: A broadband and high-gain metamaterial microstrip antenna
Authors: Li, L.-W.; Li, Y.-N.; Yeo, T.S.; Mosig, J.R.; Martin, O.J.F.
Abstract: A broad bandwidth and high gain rectangular patch antenna was specifically designed in this paper using planar-patterned metamaterial concepts. Based on an ordinary patch antenna, the antenna has isolated triangle gaps and crossed strip-line gaps etched on the metal patch and ground plane, respectively. Demonstrated to have left-handed characteristics, the patterned metal patch and finite ground plane form a coupled capacitive-inductive circuit of negative index metamaterial. It is shown to have great impact on the antenna performance enhancement in terms of the bandwidth significantly broadened from a few hundred megahertz to a few gigahertz, and also in terms of high efficiency, low loss, and low voltage standing wave ratio. Experimental data show a reasonably good agreement between the simulation and measured results. This antenna has strong radiation in the horizontal direction for some specific applications within the entire band. © 2010 American Institute of Physics.
Mon, 19 Apr 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/539162010-04-19T00:00:00Z
- A Fast Analysis of Scattering and Radiation of Large Microstrip Antenna Arrayshttps://scholarbank.nus.edu.sg/handle/10635/54125Title: A Fast Analysis of Scattering and Radiation of Large Microstrip Antenna Arrays
Authors: Yuan, N.; Yeo, T.S.; Nie, X.-C.; Li, L.W.
Abstract: An accurate and efficient method that combines the precorrected fast Fourier transform (FFT) method and the discrete complex image method (DCIM) is presented to characterize the scattering and radiation properties of arbitrarily shaped microstrip patch antennas. In this method, the mixed potential integral equation (MPIE) is discretized in the spatial domain by means of the discrete complex image method. The resultant system is solved iteratively using the generalized conjugate residual method (GCR) and the precorrected-FFT technique is used to speed up the matrix-vector multiplication. The precorrected-FFT eliminates the need to generate and store the usual square Impedance matrix and thus leads to a significant reduction in memory requirement and computational cost. Numerical results are presented for arbitrarily shaped microstrip antenna arrays to demonstrate the accuracy and efficiency of this technique.
Mon, 01 Sep 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/541252003-09-01T00:00:00Z
- Wideband bandpass filters with SAW-filter-like selectivity using chip SAW resonatorshttps://scholarbank.nus.edu.sg/handle/10635/83269Title: Wideband bandpass filters with SAW-filter-like selectivity using chip SAW resonators
Authors: Lu, X.; Mouthaan, K.; Soon, Y.T.
Abstract: Bandpass filters with surface acoustic wave (SAW)-filter-like selectivity and much wider bandwidth compared to conventional SAW filters are presented. The proposed topology consists of SAW resonator networks and parallel coupled lines. Each ladder type resonator network has a series resonator and two shunt resonators to define the upper and lower cutoff frequencies and realize the sharp passband selectivity. Analysis of the proposed SAW resonator network and a comparison with a traditional ladder type SAW filter is provided. Two filters are designed, fabricated, and measured using chip SAW resonators and microstrip coupled lines on Rogers RO4003C. As the available SAW resonators are discrete, they are connected together using 1-mil bond wires to form the SAW resonator network. The resonators are also wire bonded to the coupled lines and ground patch. The bandwidth of the two filters is 10.5% and 17%, respectively, which is much wider than conventional SAW filters with a bandwidth of a few percent. An analysis is provided for the bulk wave effects, ripples due to finite transducer, gratings of resonators, and second-order effects from series and parallel resonators, which cause deterioration of the passband performance. The impact of bond wire inductance and parasitic coupling, which cause spurious responses at the stopbands, are also discussed. © 2013 IEEE.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/832692014-01-01T00:00:00Z
- A fast combined field volume integral equation solution to EM scattering by 3-D dielectric objects of arbitrary permittivity and permeabilityhttps://scholarbank.nus.edu.sg/handle/10635/54129Title: A fast combined field volume integral equation solution to EM scattering by 3-D dielectric objects of arbitrary permittivity and permeability
Authors: Nie, X.-C.; Yuan, N.; Li, L.-W.; Gan, Y.-B.; Yeo, T.S.
Abstract: A fast solution to the combined field volume integral equation (CFVIE) for electromagnetic scattering by large three-dimensional dielectric bodies of arbitrary permittivity and permeability is presented. The CFVIE is formulated in the region of the scatterers by expressing the total fields as the sum of the incident wave and the radiated wave due to both the electric and magnetic polarization currents. The resultant integral equation is solved using the method of moments (MoM). Then the precorrected fast Fourier transform (P-FFT) method is applied to reduce the memory requirement and accelerate the matrix-vector multiplication in the MoM solution. In the implementation of the P-FFT method, two sets of projection operators are constructed respectively for the projections of the electric sources and magnetic sources. In addition, two sets of interpolation operators are also applied respectively for the computation of the vector/scalar potentials and the curl of the vector potentials in the support of the testing functions. The resultant method has a memory requirement O(N) and a computational complexity of O(Nlog N) respectively, where N denotes the number of unknowns. © 2006 IEEE.
Wed, 01 Mar 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/541292006-03-01T00:00:00Z
- Analysis of radiowave propagation in a four-layered anisotropie forest environmenthttps://scholarbank.nus.edu.sg/handle/10635/61834Title: Analysis of radiowave propagation in a four-layered anisotropie forest environment
Authors: Li, L.-W.; Koh, J.-H.; Yeo, T.-S.; Leong, M.-S.
Abstract: Propagation of electromagnetic waves in forest environments is examined in which both the transmitting and receiving points are located in the trunk layer of a four-layered anisotropic forest model. This propagation model considers the forest as a horizontally stratified, anisotropic media of canopy and trunk, bounded by ground below and air above. The electromagnetic fields are obtained using dyadic Green's functions in their eigenfunction expansion forms for an anisotropic four-layered geometry. Analytical results are found for the fields, which consist primarily of three wave modes: a direct wave, multiply reflected waves, and lateral waves. These field constituents are compared, and their domains of preponderance are calculated; it is found that the lateral wave plays a major role in communication at large distances. Radio losses for typical forest are calculated to illustrate numerical application of the forest model. Index Terms-Anisotropic media, dipole antennas, electromagnetic propagation, Green function, nonhomogeneous media. © 1999 IEEE.
Thu, 01 Jul 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/618341999-07-01T00:00:00Z
- Real-time three-dimensional modular SAR preprocessor designhttps://scholarbank.nus.edu.sg/handle/10635/57206Title: Real-time three-dimensional modular SAR preprocessor design
Authors: Chan, H.L.; Yeo, T.S.
Abstract: The architecture design for a high-speed front-end video pre-filtering is described, this being part of an effort to develop a real-time range-doppler digital SAR processor to produce image maps of the scanned area immediately as raw data are collected. The evolved architecture consists of three-dimensionally interconnected planes of modified transverse FIR parallel tapped elements. Both the range and azimuth prefilterings are performed simultaneously in a continuous input-output flow without the need to consider corner turning. The computation load has been reduced to one complex multiplication and two complex additions.
Thu, 21 Jun 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/572062001-06-21T00:00:00Z
- Improved analysis of antenna radiation from a circular aperture covered by a dielectric hemispherical radome shellhttps://scholarbank.nus.edu.sg/handle/10635/80567Title: Improved analysis of antenna radiation from a circular aperture covered by a dielectric hemispherical radome shell
Authors: Li, L.-W.; Leong, M.-S.; Zhou, L.; Yeo, T.-S.; Kooi, P.-S.
Abstract: A novel full-wave analysis of the antenna radiation due to an aperture flush-mounted on a ground plane and excited by a circular waveguide TE11 wave is presented. The aperture is further covered by a dielectric hemispherical radome. Huygens' equivalence principle and image theory are utilized to simplify the problem, and magnetic dyadic Green's functions are employed to formulate both the reactional magnetic current distribution around the aperture and the inner near-zone and outer far-zone electromagnetic fields. The idea of reactional iteration is implemented in this work, and, hence, the final equivalent source is obtained in quite a compact form. Comparison between the results obtained and those published elsewhere in the literature shows the additional contributions to the equivalent magnetic source distribution and the near- and far-zone field patterns from the feedback of the electromagnetic fields reflected from the dielectric radome. Although applied only for a simple-layer dielectric radome, the method itself is not restricted by the number of layers and can easily be extended to a multi-layered radome or dielectric inhomogeneous radome.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/805672000-01-01T00:00:00Z
- Fast analysis of electromagnetic transmission through arbitrarily shaped airborne radomes using precorrected-fft methodhttps://scholarbank.nus.edu.sg/handle/10635/82345Title: Fast analysis of electromagnetic transmission through arbitrarily shaped airborne radomes using precorrected-fft method
Authors: Nie, X.-C.; Yuan, N.; Li, L.-W.; Yeo, T.-S.; Gan, Y.-B.
Abstract: A fast technique based on the Poggio, Miller, Chang, Harrington and Wu (PMCHW) formulation and the precorrected- FFT method is presented for accurate and efficient analysis of electromagnetic transmission through dielectric radomes of arbitrary shape (including airborne radomes). The method of moments is applied to solve the integral equations in which the surfaces of the radomes are modeled using surface triangular patches and the integral equations are converted into a linear system in terms of the equivalent electric and magnetic surface currents. Next, the precorrected- FFT method, a fast approach associated with O(N1.5 logN) or less complexity, is used to eliminate the requirement of generating and storing the square impedance matrix and to speed up the matrix-vector product in each iteration of the iterative solution. Numerical results are presented to validate the implementation and illustrate the accuracy of the method.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/823452005-01-01T00:00:00Z
- Micro-motion feature extraction of target in inverse synthetic aperture radar imaging with sparse aperturehttps://scholarbank.nus.edu.sg/handle/10635/56624Title: Micro-motion feature extraction of target in inverse synthetic aperture radar imaging with sparse aperture
Authors: Luo, Y.; Zhang, Q.; Qiu, C.; Yeo, T.S.
Abstract: Micro-motion features are very useful for target recognition in inverse synthetic aperture radar (ISAR). In this paper, we propose an effective algorithm for micro-motion feature extraction in ISAR imaging with sparse aperture. The micro-Doppler effect induced by rotational micro-motion in ISAR with sparse aperture is analysed first, and then an improved four-parameter Hough transform and an Orthogonal matching pursuit decomposition method are proposed to extract the micro-motion parameters, such as rotation rate and radius. Simulations are given to demonstrate the effectiveness of the proposed algorithm. © 2013 Taylor and Francis Group, LLC.
Sun, 01 Sep 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/566242013-09-01T00:00:00Z
- Extraction of constitutive relation tensor parameters of SRR structures using transmission line theoryhttps://scholarbank.nus.edu.sg/handle/10635/55980Title: Extraction of constitutive relation tensor parameters of SRR structures using transmission line theory
Authors: Xu, W.; Li, L.-W.; Yao, H.-Y.; Yeo, T.-S.; Wu, Q.
Abstract: In this paper, the transmission line theory is utilized to characterize the metamaterials comprising of microscopic elements of a periodic array, specifically, the traditional split-ring resonators (SRRs), as an example. The bianisotropic property of the metamaterials is characterized in a new way different from the existing wave methods. As evident from both simulations and experiments, the SRR array structure is found to be quite lossy even though it is made of very good conductor or even perfect conductor as in simulation. With the present characterization, we are able to explain physically very well on how or why the energy gets lost in this structure. Finally, the theoretical result is compared with numerical simulation data obtained based on quasi-static Lorentz theory to further verify our analysis.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/559802006-01-01T00:00:00Z
- Complete scattering parameter characterisation by FDTD method of Y-junction power dividers with small output angleshttps://scholarbank.nus.edu.sg/handle/10635/61954Title: Complete scattering parameter characterisation by FDTD method of Y-junction power dividers with small output angles
Authors: Hum, P.J.; Leong, M.S.; Kooi, P.S.; Yeo, T.S.
Abstract: The finite difference time-domain method is applied to calculate the complete frequency dependent scattering matrix of microstrip Y-junctions with increasingly narrow angles between their output ports. The results of the junctions' port isolations are presented. Numerical results obtained compare favourably with experiment and published results over a wide frequency range. These results show that the angle between the output ports significantly influences the matching, transmission and isolation characteristics of the junctions. It is shown how the stability criterion can be used to calculate a suitable size of the computational domain for accurate results. Transient spatial distribution of the electric fields of the Y-junction vividly reveals the complex mechanism of substrate surface-wave generation.
Sun, 01 Oct 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/619541995-10-01T00:00:00Z
- Left-handed material effects on waves modes and resonant frequencies: Filled waveguide structures and substrate-loaded patch antennashttps://scholarbank.nus.edu.sg/handle/10635/56486Title: Left-handed material effects on waves modes and resonant frequencies: Filled waveguide structures and substrate-loaded patch antennas
Authors: Xu, W.; Li, L.-W.; Yao, H.-Y.; Yeo, T.-S.; Wu, Q.
Abstract: In this paper, we apply the Double Negative Material in some basic applications, including waveguide, rectangular patch antenna and disc patch antenna. By analyzing theoretically we find that the sizes of these equipments can be greatly reduced by using multi-block (which may include both double positive and double negative material) dielectric materials. In addition, the sizes of patch antennas are no longer proportional to the working frequency but roughly to the ratio of the thicknesses of dielectric slabs. Still some new modes in both waveguide and patch antennas are found, and by working at the new modes the bandwidth of the patch antenna can be dramatically increased.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/564862005-01-01T00:00:00Z
- FDTD analysis of a slot-loaded meandered rectangular patch antenna for dual-frequency operationhttps://scholarbank.nus.edu.sg/handle/10635/56031Title: FDTD analysis of a slot-loaded meandered rectangular patch antenna for dual-frequency operation
Authors: Gao, S.-C.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: The characteristics of a compact, dual-frequency antenna using the slot-loaded meandered rectangular microstrip patch are analysed. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. The FDTD programs are developed and validated by available measurement results. Three different dual-frequency antennas, which include the slot-loaded rectangular patch, the slot-loaded meandered rectangular patch with five slits, the slot-loaded meandered rectangular patch with 10 slits, are analysed and compared. It is shown that more slits and longer slits could lead to a smaller size of the dual-frequency antenna. The effects of slit lengths on the resonant frequencies and the frequency ratio of the slot-loaded meandered rectangular patch with 10 slits are shown. Several design curves are presented. The electric current distributions on the patch at two resonant frequencies are described, together with the results illustrating the electric field distributions under the patch. The radiation patterns of three dual-frequency antennas are also presented and compared.
Thu, 01 Feb 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/560312001-02-01T00:00:00Z
- ISAR imaging of targets with moving parts using micro-doppler detection on the range profile imagehttps://scholarbank.nus.edu.sg/handle/10635/70701Title: ISAR imaging of targets with moving parts using micro-doppler detection on the range profile image
Authors: Tan, H.S.; Changzheng, M.; Yeo, T.S.; Zhang, Q.; Ng, C.S.; Zou, B.
Abstract: In ISAR imaging, most works have assumed the target to be a rigid body, a body without any rotating, vibrating or moving parts. The rotation of structures in a target, such as the rotor of a helicopter or the turret of a tank target, may induce frequency modulation on the returned signals and generate side-bands about the center frequency of the target's body doppler frequency, known as the micro-doppler phenomenon. In this paper we present a new method based on range grouping of the target's range profile for the separation of the rotating or moving parts from the target's body. The method is carried out on the Range Profile Image, different from other methods that do the separation at the signal level. © 2007 IEEE.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/707012007-01-01T00:00:00Z
- Comments on "non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery"https://scholarbank.nus.edu.sg/handle/10635/55337Title: Comments on "non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery"
Authors: Chan, H.L.; Yeo, T.S.
Abstract: The non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight synthetic aperture radar (SAR) is discussed. QPGA speed up the estimation convergence by selectively increasing the pool of quality synchronization sources. QPGA is capable of functioning in an environment with stationary and moving targets. It focuses stationary targets even in the presence of moving targets, but also the moving targets to some extent.
Fri, 01 Nov 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/553372002-11-01T00:00:00Z
- A novel technique for the processing of short-dwell spotlight SAR datahttps://scholarbank.nus.edu.sg/handle/10635/50521Title: A novel technique for the processing of short-dwell spotlight SAR data
Authors: Wong, F.H.; Yeo, T.S.
Abstract: The range migration algorithm (RMA) is an accurate algorithm to process spotlight synthetic aperture radar (SAR) data. However, in applying the RMA to process the SAR data, especially for short-dwell data, the data length has to be extended in azimuth by zero-padding it to the length of the azimuth filter. On the other hand, the spectral analysis (SPECAN, which is a deramp followed by a fast Fourier transform) algorithm is efficient, since the data extension is unnecessary, but an assumption is made that all targets have the same FM rate and the same range cell migration. A novel algorithm is introduced here to combine the accuracy of the RMA and the efficiency of SPECAN. It involves bulk azimuth uncompressing the RMA processed data with a single linear FM filter, and then refocusing the data using SPECAN, all done without the azimuth extension in the RMA. Localized artifacts generated can be removed easily. Point target simulations, including one with a high squint angle of 60°, were successfully performed to verify the algorithm. © 2003 IEEE.
Thu, 01 May 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/505212003-05-01T00:00:00Z
- High-Resolution Bistatic ISAR Imaging Based on Two-Dimensional Compressed Sensinghttps://scholarbank.nus.edu.sg/handle/10635/123458Title: High-Resolution Bistatic ISAR Imaging Based on Two-Dimensional Compressed Sensing
Authors: Zhang, Shunsheng; Zhang, Wei; Zong, Zhulin; Tian, Zhong; Yeo, Tat Soon
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1234582015-01-01T00:00:00Z
- Accurate analysis of conformal antenna arrays with finite and curved frequency selective surfaceshttps://scholarbank.nus.edu.sg/handle/10635/54862Title: Accurate analysis of conformal antenna arrays with finite and curved frequency selective surfaces
Authors: Yuan, N.; Nie, X.-C.; Gan, Y.-B.; Yeo, T.-S.; Li, L.-W.
Abstract: In this paper, a full-wave volume-surface integral equation approach is presented for the analysis of conformal microstrip antenna arrays with finite curved frequency selective surface (FSS) radomes. The volume integral equation is applied to the dielectric region of the composite structure, while the surface integral equation is used on the conductive surface. The integral equations are solved using the method of moments (MoM), with the precorrected-FFT (P-FFT) method used to reduce the memory requirement and accelerate the matrix-vector products in the iterative solution of the equation. With this method, FSSs and antennas of arbitrary shape and finite size can be modelled and the effects of the FSS on the characteristics of the antenna can be accurately investigated. © 2007 VSP.
Mon, 01 Oct 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/548622007-10-01T00:00:00Z
- Propagation property analysis of metamaterial constructed by conductive SRRs and wires using the MGS-based algorithmhttps://scholarbank.nus.edu.sg/handle/10635/82938Title: Propagation property analysis of metamaterial constructed by conductive SRRs and wires using the MGS-based algorithm
Authors: Yao, H.-Y.; Xu, W.; Li, L.-W.; Wu, Q.; Yeo, T.-S.
Abstract: An efficient numerical algorithm based on the modified Gram-Schmidt (MGS) procedure is developed in this paper to solve the electrical-field integral equation for characterizing metamaterials. The method of moments (MoM) with rooftop basis functions is implemented in the integral-equation solver. The MGS-based algorithm is implemented into the solver for decomposing the local MoM dense matrix without prior knowledge of the matrix elements. Although each element of the metamaterials is electrically small in size, the number of elements is very large so that the number of unknowns for characterizing the metamaterials is very large. Even so, this algorithm in the MoM solver has demonstrated via examples to be efficient and accurate. Numerical results on the number N of unknowns show that the CPU time per iteration and the memory requirements are both reduced from O(N 2) to O(N 1.5). After implementing this algorithm in the solver, propagation characteristics are finally presented when electromagnetic waves pass through a metamaterial prism that is synthesized using square split-ring resonators and wires in free space. © 2005 IEEE.
Fri, 01 Apr 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/829382005-04-01T00:00:00Z
- On the eigenfunction expansion of electromagnetic dyadic green's functions in rectangular cavities and waveguideshttps://scholarbank.nus.edu.sg/handle/10635/80875Title: On the eigenfunction expansion of electromagnetic dyadic green's functions in rectangular cavities and waveguides
Authors: Li, L.W.; Kooi, P.S.; Leong, M.S.; Yeo, T.S.; Ho, S.L.
Abstract: The electric dyadic Green's functions of both the first and the second kinds due to the presence of electric and equivalent magnetic sources in rectangular cavities are obtained. A method for directly reducing the dyadic Green's functions for a rectangular cavity to those for a semi-infinite and an infinite rectangular waveguides is presented. The Green dyads of the second kind for an infinite and a semi-infinite rectangular waveguides, and a rectangular cavity are obtained.
Wed, 01 Mar 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/808751995-03-01T00:00:00Z
- Small dual-frequency microstrip antennashttps://scholarbank.nus.edu.sg/handle/10635/57431Title: Small dual-frequency microstrip antennas
Authors: Gao, S.-C.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: The characteristics of a dual-frequency compact antenna, which uses a rectangular microstrip patch with a shorting pin, are studied. Compared with the conventional rectangular patch antenna, this antenna can achieve both a significant reduction of antenna size and a dual-frequency operation with a single feed. A detailed parameter study is performed. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. The FDTD codes are developed and validated by measurement results. One antenna has designed and fabricated, and the comparisons between the measured results and the calculated results are provided. The effects of several antenna parameters on two resonant frequencies, frequency ratio, and radiation pattern characteristics of the antenna have been analyzed and compared. Results of the return loss are also presented. It is shown that various frequency ratios (2.82-4.23) can be obtained by varying the design parameters of this antenna. Several design curves are also presented.
Tue, 01 Jan 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/574312002-01-01T00:00:00Z
- On the integral identities consisting of two spherical Bessel functionshttps://scholarbank.nus.edu.sg/handle/10635/82815Title: On the integral identities consisting of two spherical Bessel functions
Authors: Qiu, C.-W.; Li, L.-W.; Zouhdi, S.; Yeo, T.-S.; Wu, Q.
Abstract: When deriving dyadic Green's functions for the spherical structures with gyrotropic or bianisotropic materials, an integral whose integrand function consists of two spherical Bessel functions and a power function needs to be evaluated. Therefore, this paper revisits thoroughly the evaluation of the integral of Il,l′(K,K′). Starting from pointing out an error, it provides the correct solution to the integral in spherical coordinates in terms of distribution, in particular, step functions and delta functions. The formulation is further extended to a more generalized integral Hl,l′ lambda;(K,K′). and it is newly found that the solution to the generalized integral varies differently in the cases of even and odd values of l - l′. The mistakes that we found in the previous literature can also be proved easily by some of our intermediate solutions. © 2007 IEEE.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/828152007-01-01T00:00:00Z
- Wide-band microstrip antenna with an H-shaped coupling aperturehttps://scholarbank.nus.edu.sg/handle/10635/57816Title: Wide-band microstrip antenna with an H-shaped coupling aperture
Authors: Gao, S.-C.; Li, L.-W.; Leong, M.-S.; Yeo, T.-S.
Abstract: Theoretical and experimental results of a wide-band planar antenna are presented. This antenna can achieve a wide bandwidth, low cross-polarization levels, and low backward radiation levels. For wide bandwidth and easy integration with active circuits, it uses aperture-coupled stacked square patches. The coupling aperture is an H-shaped aperture. Based on the finite difference time-domain method, a parametric study of the input impedance of the antenna is presented, and effects of each parameter on the antenna impedance are illustrated. One antenna is also designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of 21.7%. The cross-polarization levels in both E and H planes are better than -23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results of S parameters and radiation patterns are presented and discussed.
Tue, 01 Jan 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/578162002-01-01T00:00:00Z
- Time-frequency imaging algorithm for high-speed spinning targets in two dimensionshttps://scholarbank.nus.edu.sg/handle/10635/57673Title: Time-frequency imaging algorithm for high-speed spinning targets in two dimensions
Authors: Li, J.; Qiu, C.-W.; Zhang, L.; Xing, M.; Bao, Z.; Yeo, T.-S.
Abstract: This study focuses on the narrow-band radar imaging for high-speed spinning targets. Based on the time-frequency characteristic of the echoed signal, a novel coherent spectrogram redistribution method, coherent single range Doppler interferometry (CSRDI), is proposed, which is capable of generating high-resolution imagery by applying a phase matched processing. Furthermore, the approach performs well at low signal-to-noise ratio. The spinning rate error is also taken into consideration and an estimation approach based on the focal entropy is proposed. The validity is confirmed by real data and numerical simulations. © 2010 © The Institution of Engineering and Technology.
Wed, 01 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576732010-12-01T00:00:00Z
- A novel multifractal estimation method and its application to remote image segmentationhttps://scholarbank.nus.edu.sg/handle/10635/54633Title: A novel multifractal estimation method and its application to remote image segmentation
Authors: Du, G.; Yeo, T.S.
Abstract: Based on the gliding-box and relative differential box-counting algorithms, a novel method that estimates accurately the multifractal exponents, a distinct characteristics of gray-scale digital images, is proposed. Four natural texture images are used to test the performance of the novel multifractal measure. Comparisons with published methods show that the proposed method can efficiently describe texture images and can provide accurate classification results.
Mon, 01 Apr 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/546332002-04-01T00:00:00Z