ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 25 Jan 2020 05:46:45 GMT2020-01-25T05:46:45Z503711- 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
- Focusing of tandem bistatic-configuration data with range migration algorithmhttps://scholarbank.nus.edu.sg/handle/10635/56077Title: Focusing of tandem bistatic-configuration data with range migration algorithm
Authors: Wu, Q.; Liang, Y.; Xing, M.; Qiu, C.; Bao, Z.; Yeo, T.-S.
Abstract: A bistatic range migration algorithm (RMA) based on an exact analytical bistatic point-target (PT) spectrum in the tandem configuration is proposed in this letter. For the conventional geometry-based bistatic formula method, the derived spectrum is only a quasi-analytical one because a variable called half-quasi-bistatic angle (HQBA) is not exactly analytically expressed. The key step of the proposed algorithm is to deduce an analytical HQBA in the tandem configuration, and thus, an exact analytical closed-form PT spectrum is acquired. Based on this analytical spectrum, a bistatic RMA is presented. It is demonstrated that this algorithm can handle the bistatic tandem configuration with extremely large baseline/range ratio and can also be applied to wide-swath imaging. © 2010 IEEE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/560772011-01-01T00:00:00Z
- ISAR imaging in strong ground clutter using a new stepped-frequency signal formathttps://scholarbank.nus.edu.sg/handle/10635/56417Title: ISAR imaging in strong ground clutter using a new stepped-frequency signal format
Authors: Zhang, Q.; Yeo, T.S.; Du, G.
Abstract: In this paper, a new easy-to-implement variant of stepped-frequency signal format is presented for ground clutter cancellation application. A sequence of pulse-groups, where each pulse-group consists of two pulses of the same carrier frequency, is transmitted. The carrier frequency of each subsequent burst is stepped at Δf. Simple first-order cancellation of ground clutter can be carried out by comparing the returns of the two adjacent pulses, as the clutter movement (due to wind, etc.) can be assumed negligible within this interval (typically < 1 μs). A computer simulation is given to illustrate the effectiveness of the proposed method. © 2003 IEEE.
Thu, 01 May 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/564172003-05-01T00:00:00Z
- 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
- 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
- Eigenfunctional representation of dyadic Green's functions in multilayered gyrotropic chiral mediahttps://scholarbank.nus.edu.sg/handle/10635/55810Title: Eigenfunctional representation of dyadic Green's functions in multilayered gyrotropic chiral media
Authors: Qiu, C.-W.; Yao, H.-Y.; Li, L.-W.; Zouhdi, S.; Yeo, T.-S.
Abstract: Studying electromagnetic waves in complex media has been an important research topic due to its useful applications and scientific significance of its physical performance. Dyadic Green's functions (DGFs), as a mathematical kernel or a dielectric medium response, have long been a valuable tool in solving both source-free and source-incorporated electromagnetic boundary value problems for electromagnetic scattering, radiation and propagation phenomena. A complete eigenfunctional expansion of the dyadic Green's functions for an unbounded and a planar, arbitrary multilayered gyrotropic chiral media is formulated in terms of the vector wavefunctions. After a general representation of Green's dyadics is obtained, the scattering coefficients of Green's dyadics are determined from the boundary conditions at each interface and are expressed in a greatly compact form of recurrence matrices. In the formulation of Green's dyadics and their scattering coefficients, three cases are considered, i.e. the current source is immersed in (1) the first, (2) the intermediate, and (3) the last regions, respectively. Although the dyadic Green's functions for an unbounded gyroelectric medium has been reported in the literature, we here present not only unbounded but also multilayered DGFs for the gyrotropic chiral media. The explicit representation of the DGFs after reduction to the gyroelectric or isotropic case agrees well with those existing corresponding results. © 2007 IOP Publishing Ltd.
Fri, 25 May 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/558102007-05-25T00:00:00Z
- Interline coupling of ultra-high-speed pulse propagating on PCBhttps://scholarbank.nus.edu.sg/handle/10635/80622Title: Interline coupling of ultra-high-speed pulse propagating on PCB
Authors: Yeo, T.S.; Ng, C.S.; Leong, M.S.; Kooi, P.S.
Abstract: Interline coupling of ultra-high-speed pulse propagating on PCB was investigated parametrically using a formulation based on the difference in the odd-mode and even-mode propagation speeds. Results show that the coupling effect does not decrease monotonically with increasing line spacing.
Sun, 01 Aug 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/806221993-08-01T00:00:00Z
- 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
- Analysis of metallic waveguides of a large class of cross sections using polynomial approximation and superquadric functionshttps://scholarbank.nus.edu.sg/handle/10635/55086Title: Analysis of metallic waveguides of a large class of cross sections using polynomial approximation and superquadric functions
Authors: Lin, S.-L.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: By using the polynomial approximation and superquadric functions in the Rayleigh-Ritz procedure, a unified method has been proposed to analyze conducting hollow waveguides of a large class of cross sections in our previous paper. Some useful and complicated cross-sectional waveguides in the microwave system, namely, eccentric annular, pentagonal, L-shaped, single-ridged, and double-ridged waveguides are analyzed in this paper. Compared with other numerical methods, this method has the advantages of straightforward, accurate, and computational effective.
Fri, 01 Jun 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/550862001-06-01T00:00:00Z
- RCS computation of composite conducting-dielectric objects with junctions using the hybrid volume-surface integral equationhttps://scholarbank.nus.edu.sg/handle/10635/51021Title: RCS computation of composite conducting-dielectric objects with junctions using the hybrid volume-surface integral equation
Authors: Yuan, N.; Yeo, T.-S.; Nie, X.-C.; Li, L.-W.
Abstract: The hybrid volume-surface integral equation (VSIE) combined with the Method of Moments (MoM) is applied to the analysis of scattering from arbitrarily composite conducting-dielectric objects with conducting-dielectric or dielectric-dielectric junctions. The electric field volume integral equation is applied to the material region and the electric field surface integral equation is enforced over the conducting surface. Compared to the surface integral equation (SIE), the VSIE is more efficient and convenient since the formulation of the VSIE retains the same simple form regardless of the complexity of the object and materials, and no extra treatment is required when dealing with junction problems.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/510212005-01-01T00:00:00Z
- 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
- Three-dimensional ISAR imaging using a two-dimensional sparse antenna arrayhttps://scholarbank.nus.edu.sg/handle/10635/57660Title: Three-dimensional ISAR imaging using a two-dimensional sparse antenna array
Authors: Ma, C.; Yeo, T.S.; Tan, H.S.; Wang, J.; Chen, B.
Abstract: Conventional antenna array 3-D inverse synthetic aperture radar (ISAR) imaging method does imaging by first carrying out ISAR imaging for all the different antennas and then using array direction of arrival (DOA) estimation on every scatterer to get the position of that scatterer. The aperture formed by the target's motion is used to separate the scatterers, and the antenna array aperture is used for position measurement. In this letter, a 3-D imaging method based on a combination of sparse array beamforming and ISAR imaging is proposed, where 3-D images are formed by space-time match filtering. The estimation of the target's rotation parameters is also given. Simulation results have shown the effectiveness of the proposed methods. © 2008 IEEE.
Tue, 01 Jul 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576602008-07-01T00:00:00Z
- 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
- General expression of dyadic Green's functions in radially multilayered chiral mediahttps://scholarbank.nus.edu.sg/handle/10635/80491Title: General expression of dyadic Green's functions in radially multilayered chiral media
Authors: Li, Le-Wei; Kooi, Pang-Shyan; Leong, Mook-Seng; Yeo, Tat-Soon
Abstract: A general expression of spectral-domain dyadic Green's function (DGF) is presented in this paper for defining the electromagnetic radiation fields in spherically arbitrary multilayered and chiral media. Without any loss of the generality, each of the radial multilayers could be the chiral layer with different permittivity, permeability, and chirality admittance, while both distribution and location of current sources are assumed to be arbitrary. The DGF is composed of the unbounded DGF and the scattering DGF, based on the method of scattering superposition. The scattering DGF in each layer is constructed in terms of the modified and normalized spherical vector wave functions. The coefficients of the scattering DGF's are derived and expressed in terms of the equivalent reflection and transmission coefficients, by applying boundary conditions satisfied by the coefficient matrices.
Wed, 01 Mar 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/804911995-03-01T00:00:00Z
- Dual-polarized slot-coupled planar antenna with wide bandwidthhttps://scholarbank.nus.edu.sg/handle/10635/55708Title: Dual-polarized slot-coupled planar antenna with wide bandwidth
Authors: Gao, S.-C.; Li, L.-W.; Leong, M.-S.; Yeo, T.-S.
Abstract: A new dual-polarized slot-coupled microstrip patch antenna is presented, which can achieve high-isolation low cross-polarization levels, a wide bandwidth, and low backward radiation levels. The coupling slot is an H-shaped slot. For wide bandwidth and easy integration with active circuits, it uses the slot-coupled stacked microstrip patches. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. First, a parametric study on the input impedance of the antenna with a single input port is presented. Based on the results, a dual-polarized microstrip antenna is designed, fabricated, and then measured. The measured return loss exhibits an impedance bandwidth of over 20.9% and the isolation between two polarization ports is better than 36 dB over the bandwidth. The cross-polarization levels in both E and H planes are better than 22 dB. The front-to-back ratio of the antenna radiation pattern is better than 21 dB. Both theoretical and experimental results of return loss, isolation, and radiation patterns are presented and discussed.
Sat, 01 Mar 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/557082003-03-01T00:00:00Z
- Multiple penetration of a TEz-polarized plane wave into multilayered cylindrical cavity-backed apertureshttps://scholarbank.nus.edu.sg/handle/10635/80763Title: Multiple penetration of a TEz-polarized plane wave into multilayered cylindrical cavity-backed apertures
Authors: Yin, W.-Y.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: A generalized mathematical procedure is developed for investigating a TEz-polarized plane wave penetration through two-dimensional (2-D) multilayered cylindrical cavity-backed apertures. The mathematical treatment is based on the direct integral equation technique combined with the Galerkin's procedure. Both the near- and far-zone field solutions to such a multiple coupling system are obtained in an analytical form. By taking the aperture edge effects into account, the magnetic currents on the surrounded multiple apertures are expanded in terms of a series of Chebyshev polynomials of the first kind. Furthermore, parametric studies are performed to show the variation of the penetrated near-zone magnetic field in various cylindrical cavity-backed apertures with the aperture number and geometrical sizes.
Wed, 01 Nov 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/807632000-11-01T00:00:00Z
- Sparse array 3-D ISAR imaging based on maximum likelihood estimation and CLEAN techniquehttps://scholarbank.nus.edu.sg/handle/10635/57455Title: Sparse array 3-D ISAR imaging based on maximum likelihood estimation and CLEAN technique
Authors: Ma, C.; Yeo, T.S.; Tan, C.S.; Tan, H.S.
Abstract: Large 2-D sparse array provides high angular resolution microwave images but artifacts are also induced by the high sidelobes of the beam pattern, thus, limiting its dynamic range. CLEAN technique has been used in the literature to extract strong scatterers for use in subsequent signal cancelation (artifacts removal). However, the performance of DFT parameters estimation based CLEAN algorithm for the estimation of the signal amplitudes is known to be poor, and this affects the signal cancelation. In this paper, DFT is used only to provide the initial estimates, and the maximum likelihood parameters estimation method with steepest descent implementation is then used to improve the precision of the calculated scatterers positions and amplitudes. Time domain information is also used to reduce the sidelobe levels. As a result, clear, artifact-free images could be obtained. The effects of multiple reflections and rotation speed estimation error are also discussed. The proposed method has been verified using numerical simulations and it has been shown to be effective. © 2006 IEEE.
Sun, 01 Aug 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/574552010-08-01T00:00:00Z
- A comparative study of radio wave propagation over the earth due to a vertical electric dipolehttps://scholarbank.nus.edu.sg/handle/10635/81847Title: A comparative study of radio wave propagation over the earth due to a vertical electric dipole
Authors: Fei, T.; Li, L.-W.; Yeo, T.-S.; Wang, H.-L.; Wu, Q.
Abstract: A comparative study of the electromagnetic field excited by a vertical electric dipole on the earth is presented. Four sets of formulas for both the planar earth model and the spherical earth model (of large radius) are compared to find out their valid ranges. Numerical computations are also carried out specifically for a three-layered earth model. For the planar earth model, when both the source and observation points are on the surface, and the planar earth covered with a thick-enough dielectric layer, the method by Zhang is more accurate; while for the fields above the surface and the thin-enough dielectric layer, the method by King and Sandler is more accurate. However, the hybrid of the trapped surface wave and the lateral wave were exhibited in the curves in, but they were not shown in the curves. Numerical calculation also shows that the amplitude of the trapped surface wave attenuates as ρ-1/2 in the ρ direction as expected. However, the lateral wave given by does not exhibit ρ-1/2 decay in the direction. For the layered spherical earth model, the exact series summation, which serves as an exact solution to the classic problem, is computed and compared with the residue series. Numerical results show that the residue series gives a good approximation to the field, but the smooth curve illustrates that the hybrid effect due to the trapped surface wave and the lateral wave was ignored in literature. The field strength of the trapped surface wave decreases with the dielectric layer thickness and is affected by the curvature of the earth. The exact series shows the oscillation of the field caused by the hybrid effects, which can be considered as the dielectric resonance between the upper and lower dielectric interfaces when it is guided to propagate, but none of the other three approximations can depict the effects. © 2007 IEEE.
Mon, 01 Oct 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/818472007-10-01T00:00:00Z
- The Penetrated and Scattered Field Distributions in the Presence of a Nonuniform Cold Magnetized Plasma Column Surrounded by Multiple Apertures: TE-Wave Incidencehttps://scholarbank.nus.edu.sg/handle/10635/57631Title: The Penetrated and Scattered Field Distributions in the Presence of a Nonuniform Cold Magnetized Plasma Column Surrounded by Multiple Apertures: TE-Wave Incidence
Authors: Yin, W.-Y.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: Due to a TE-wave normal incidence, the penetrated and scattered fields in the presence of a nonuniform cold magnetized plasma column are investigated in this work. The mathematical treatment is based on the direct integral equation formulated for describing the currents on the surrounded multiple apertures of the plasma column. To formulate such an integral equation, two-dimensional magnetic dyadic Green's functions in multilayered cylindrical shells are derived in terms of the cylindrical vector wave functions. By using Galerkin's method, the magnetic currents on all apertures are expanded in the form of a series of Chebyshev polynomials of the first kind, and furthermore, parameter effect studies are performed to show the variation of the near- and far-zone fields with the changing of the operating frequency, angular width, and number of the surrounded apertures.
Tue, 01 May 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576312001-05-01T00:00:00Z
- An efficient TCS formula for rainfall microwave attenuation: T-matrix approach and 3-D fitting for oblate spheroidal raindropshttps://scholarbank.nus.edu.sg/handle/10635/61804Title: An efficient TCS formula for rainfall microwave attenuation: T-matrix approach and 3-D fitting for oblate spheroidal raindrops
Authors: Seow, Y.-L.; Li, L.-W.; Leong, M.-S.; Kooi, P.-S.; Yeo, T.-S.
Abstract: The T-Matrix approach toward the computation of total cross sections of spheroidal raindrops due to electromagnetic scattering is considered numerically exact, and has therefore been used in this paper for the analysis of the total cross section (TCS) of the spheroidal raindrops. A more accurate computer programme based on the T-Matrix method has been developed in MATHEMATICA™ so as to evaluate the TCS's of the spheroidal raindrop scatterers. With the checked programme after comparison, a large amount of TCS data has been obtained and plotted in a three-dimensional (3-D) graphic in this paper. Utilizing these exact data points, a 3-D (or two-step) nonlinear least squares fitting procedure has been proposed and implemented successfully. As a result, an efficient formula of the TCS as a function of both raindrop mean radius and operating frequency has been obtained. In the analysis, four cases (both parallel and perpendicular polarizations, and outdoor temperatures of 10 and 20 °C) are considered. Covering a very large validity range for practical useful problems, this formula is very compact, easy to use, and very much faster (by about two orders of magnitude) than the conventional algorithm. © 1998 IEEE.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/618041998-01-01T00:00:00Z
- 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
- 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
- Transient interference excision in over-the-horizon radar using adaptive time-frequency analysishttps://scholarbank.nus.edu.sg/handle/10635/57699Title: Transient interference excision in over-the-horizon radar using adaptive time-frequency analysis
Authors: Guo, X.; Sun, H.; Yeo, T.S.
Abstract: The performance of over-the-horizon radars (OTHRs) degrades significantly due to transient interferences such as lightnings, meteor echoes, and man-made impulse bursts. The conventional techniques used to suppress these transient interferences generally follow a simple time-domain procedure which first localizes the transient, sets the corrupted time samples to zero, and follows by data reconstruction via interpolations. However, for an OTHR operation with a short coherent integration time (CIT) of a few seconds, the transient interference may corrupt a significant portion of the received data such that data interpolation can become erroneous. In this paper, a new transient interference excision technique is proposed. It utilizes the adaptive time-frequency analysis technique to parameterize the radar signal. The transient interference can then be identified and subsequently removed via their characteristic parameters. No data interpolation is needed. The performance of the proposed technique is illustrated by simulated and experimental OTHR data. © 2005 IEEE.
Fri, 01 Apr 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/576992005-04-01T00:00:00Z
- 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
- 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
- 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
- A unified modal analysis of off-centered waveguide junctions with thick irishttps://scholarbank.nus.edu.sg/handle/10635/54838Title: A unified modal analysis of off-centered waveguide junctions with thick iris
Authors: Lin, S.-L.; Li, L.-W.; Yeo, T.-S.; Leong, M.-S.
Abstract: In this paper, the unified mode-matching technique for concentric waveguide junction analysis is extended to calculate the scattering parameters at off-centered step discontinuities in waveguides. Because the modal fields in both waveguides are expressed accurately by polynomials in mono coordinate system, the analytical expressions of the coupling coefficients are easily obtained. Furthermore, all waveguides are tacked with in a unified manner. Comparison with the data available in literature demonstrates the accuracy and flexibility of the present method.
Sat, 01 Sep 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/548382001-09-01T00:00:00Z
- 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
- 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
- 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
- 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
- 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
- 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
- Radio wave propagation along mixed paths through a four-layered model of rain forest: an analytic approachhttps://scholarbank.nus.edu.sg/handle/10635/62671Title: Radio wave propagation along mixed paths through a four-layered model of rain forest: an analytic approach
Authors: Li, L.-W.; Yeo, T.-S.; Kooi, P.-S.; Leong, M.-S.
Abstract: This paper presents a novel full-wave analysis of the radio waves that are excited from a dipole antenna located in the trunk layer and propagate inside a four-layered forest medium. The dyadic Green's functions for the four-layered geometry are applied first to derive the integral expression of the electric fields. The closed form of the electric fields is then obtained by using the quasi-static approximation, saddle-point technique, and branch-cut integrations in the complex plane and, hence, expressed in terms of direct waves, multiple reflected waves, and lateral waves. Two kinds of images, i.e., the quasi-dynamic and complex images, are considered in the integration in the complex plane. Among those waves excited by a dipole antenna in the four-layered medium, it is shown theoretically and numerically that the lateral wave along the upper-side air-canopy interface plays a role of dominant modes. Propagation mechanism of other lateral waves due to the air-canopy, canopy-trunk, and trunk-ground interfaces is also discussed and analyzed so as to gain an insight into the wave characteristics. Transmission losses of the lateral waves are calculated numerically.
Wed, 01 Jul 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/626711998-07-01T00:00:00Z
- 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
- Calculation of spatial-domain Green functions for multilayered media using DCIM with automatic handling of surface wave poleshttps://scholarbank.nus.edu.sg/handle/10635/55247Title: Calculation of spatial-domain Green functions for multilayered media using DCIM with automatic handling of surface wave poles
Authors: Liu, Y.; Li, L.-W.; Yeo, T.-S.; Kooi, P.-S.; Leong, M.-S.
Abstract: The discrete complex image method (DCIM) has been used extensively for the calculation of spatial-domain Green functions for one-layer or two-layer media. However, one difficulty in applying DCIM to general multilayered media is the lack of a reliable procedure for the extraction of surface wave components. In the paper, the spectral-domain potential Green functions for a general multilayered medium are reformulated so that their denominators are obtained in an iterative form. A two-stage root-searching procedure is proposed for seeking the roots of these denominators. The residuals associated with the surface wave poles are calculated through contour integration. Special methods for handling the branch cuts close to the surface wave poles are discussed. Numerical examples of different geometries are given to reveal the behaviour of the surface wave poles and verify the method.
Tue, 01 Jun 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/552472004-06-01T00:00:00Z
- 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
- 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
- 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
- Circular cylindrical waveguide filled with uniaxial anisotropic media - Electromagnetic fields and dyadic Green's functionshttps://scholarbank.nus.edu.sg/handle/10635/55294Title: Circular cylindrical waveguide filled with uniaxial anisotropic media - Electromagnetic fields and dyadic Green's functions
Authors: Li, L.-W.; Liu, S.; Leong, M.-S.; Yeo, T.-S.
Abstract: Electromagnetic fields in a circular cylindrical conducting waveguide filled with uniaxial anisotropic media are formulated in this paper by using Fourier transformations. These fields are obtained as a superposition of the TE (or ordinary) and TM (or extraordinary) modes satisfying, respectively, different characteristic equations. Lastly, the dyadic Green's function is derived using the Ohm-Rayleigh method and represented by vector wave functions expansion.
Sun, 01 Jul 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/552942001-07-01T00:00:00Z
- Two-dimensional transient model for prediction of arteriolar NO/O2 modulation by spatiotemporal variations in cell-free layer widthhttps://scholarbank.nus.edu.sg/handle/10635/127638Title: Two-dimensional transient model for prediction of arteriolar NO/O2 modulation by spatiotemporal variations in cell-free layer width
Authors: Huang G.-L.; Chio T.-H.; Hui H.-T.; Yeo T.-S.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1276382015-01-01T00:00:00Z
- Radio wave propagation along earth-space paths in the presence of a multilayered anisotropic foresthttps://scholarbank.nus.edu.sg/handle/10635/57187Title: Radio wave propagation along earth-space paths in the presence of a multilayered anisotropic forest
Authors: Li, L.-W.; Lee, C.-K.; Yeo, T.-S.; Leong, M.-S.
Abstract: Propagation of electromagnetic waves along earth-space paths in forest environments is analyzed in this paper, where the transmitter is placed in the air region above the vegetation, while the receiver may be in the air region or within the vegetation. This propagation model considers the forest as a horizontally stratified, anisotropic medium of canopy and trunk, bounded by ground below and air above. Dyadic Green's functions in their eigenfunction 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 direct wave, multiply reflected waves, and lateral waves. Propagation mechanisms of these waves are studied and radio losses in a typical forest are calculated numerically.
Mon, 01 Apr 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/571872002-04-01T00:00:00Z
- Development of a SAR digital systemhttps://scholarbank.nus.edu.sg/handle/10635/62034Title: Development of a SAR digital system
Authors: Yeo, T.S.; Zhang, C.B.; Lu, Y.H.; Ren, T.
Abstract: A data acquisition system for an airborne SAR (Synthetic Aperture Radar) was designed and implemented. DSP is used for the first time in the implementation of a SAR data acquisition system. A novel precision programmable timer using the DDS (Direct Digital Synthesis) technique was designed, built, and successfully tested to provide increased flexibility, reliability and stability.
Sat, 01 May 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/620341999-05-01T00:00:00Z
- 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
- 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
- Input Impedance of a Coaxial Probe Located Inside a Rectangular Cavity: Theory and Experimenthttps://scholarbank.nus.edu.sg/handle/10635/50568Title: Input Impedance of a Coaxial Probe Located Inside a Rectangular Cavity: Theory and Experiment
Authors: Leong, M.S.; Li, L.W.; Kooi, P.S.; Yeo, T.S.; Ho, S.L.
Abstract: In this work, theoretical and experizmental analyzes of input impedance of a coaxial probe located in a rectangular cavity are presented. The technique of dyadic Green function (DGF) and the method of moments (MM) are applied in the theoretical analysis. For the magnetic equivalent source with a ŷ-dirccted discontinuity, two alternative representations of magnetic DGF for a rectangular cavity are derived in this paper. Numerical input reactance and phase of the reflection coefficient at the base of the probe obtained using both the conventional form and the alternative representations of the DGF are compared with the experimental data collected. It is found that the computed results obtained utilizing alternative DGF's agree better with the measured data. © 1996 IEEE.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/505681996-01-01T00:00:00Z
- Precorrected-FFT solution of the volume integral equation for 3-D inhomogeneous dielectric objectshttps://scholarbank.nus.edu.sg/handle/10635/57109Title: Precorrected-FFT solution of the volume integral equation for 3-D inhomogeneous dielectric objects
Authors: Nie, X.-C.; Li, L.-W.; Yuan, N.; Yeo, T.S.; Gan, Y.-B.
Abstract: This paper presents a fast solution to the volume integral equation for electromagnetic scattering from three-dimensional inhomogeneous dielectric bodies by using the precorrected-fast Fourier transform (FFT) method. The object is modeled using tetrahedral volume elements and the basis functions proposed by Schaubert et al. are employed to expand the unknown electric flux density. The basis functions are then projected onto a fictitious uniform grid surrounding the nouniform mesh, enabling the FFT to be used to speed up the matrix-vector multiplies in the iterative solution of the matrix equation. The resultant method greatly reduces the memory requirement to O(N) and the computational complexity to O(N log N), where N is the number of unknowns. As a result, this method is capable of computing electromagnetic scattering from large complex dielectric objects. © 2005 IEEE.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/571092005-01-01T00:00:00Z
- Interference cancellation for high-frequency surface wave radarhttps://scholarbank.nus.edu.sg/handle/10635/56373Title: Interference cancellation for high-frequency surface wave radar
Authors: Guo, X.; Sun, H.; Yeo, T.S.
Abstract: The performance of high-frequency surface wave radar (HFSWR) is known to suffer from external environmental interference and noise, such as cochannel radio-frequency interference from other radiating source, ionospheric clutter, lightning impulsive noise, etc. This paper experimentally evaluates the interference cancellation performance of various adaptive beamforming schemes with respect to the aforementioned three types of interferences in an attempt to find the most promising adaptive cancellation scheme in practical HFSWR environment. © 2008 IEEE.
Tue, 01 Jul 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/563732008-07-01T00:00:00Z
- 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
- Electromagnetic dyadic Green's function in spherically multilayered mediahttps://scholarbank.nus.edu.sg/handle/10635/62118Title: Electromagnetic dyadic Green's function in spherically multilayered media
Authors: Li, Le-Wei; Kooi, Pang-Shyan; Leong, Mook-Seng; Yeo, Tat-Soon
Abstract: A spectral-domain dyadic Green's function constructed for defining the electromagnetic fields in spherically multilayered media is considered by assuming that distribution and location of current sources are arbitrary. The scattering dyadic Green's function in each layer is constructed in terms of the spherical vector wave functions by applying the method of scattering superposition. The coefficients of the scattering dyadic Green's functions, based on the coupling recurrence equations satisfied by the coefficient matrix, are derived and expressed in terms of the equivalent reflection and transmission coefficients. The general solution has been applied to specific geometries, e.g., two-, three- and four-layered media that are frequently employed to model the practical problems, and the coefficients of the scattering dyadic Green's functions are presented.
Thu, 01 Dec 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/621181994-12-01T00:00:00Z