-
[show abstract]
[hide abstract]
ABSTRACT: A new method named fast directional multilevel algorithm is proposed for analyzing wave scattering. Similar to a fast multipole method, an oct-tree structure is used in the new method. Unlike the conventional MLFMA, the kernel is evaluated by a new method, instead of approximating the Green's function by multipole expansion. The fast directional multilevel algorithm is first used to solve the wave scattering problem via combined field integral equation (CFIE) using Rao-Wilton-Glisson (RWG) basis functions. The low rank representations are extended to apply in the low frequency regime which is proved efficient and stable. The numerical results demonstrate that the computational complexity of this new multilevel algorithm can achieve the complexity of O(N log N). This algorithm is robust and performs well on other oscillatory kernels because of its not depending on the explicit form of kernels.
IEEE Transactions on Antennas and Propagation 08/2011; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A backfire-to-broadside beam-scanning antenna with a periodic structure is described. The proposed antenna consists of the offset double-sided parallel-strip lines (DSPSL). The characteristics of the offset DSPSL have been studied, and then a series of offset DSPSL have been applied as the periodic antenna with a backfire-to-broadside symmetrical beam scanning capability. Both in plane and plane, main beams symmetrically steer from the backfire direction to the broadside direction with the increase of the operating frequency. The fractional impedance bandwidth has been broadened to nearly 50% by using the offset DSPSL structure.
IEEE Transactions on Antennas and Propagation 12/2010; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new method is presented to locate the poles of the Green's functions for a general multilayered medium, whether lossy or lossless. The problem associated with the pole extraction is reduced to solve the contour integrals in the complex plane that are represented in terms of the spectral-domain transmission coefficients. With the help of Cauchy's theorem, the proposed method can accurately and rapidly find all surface wave poles with a few contour integrals. The numerical examples are performed to show the efficiency of the method.
IEEE Transactions on Antennas and Propagation 08/2010; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this study, the finite-element boundary integral (FE-BI) method is applied to analyse the electromagnetic scattering from arbitrary objects in the half-space environment. Combined with the real image method to approximate the half-space Green's function, the half-space FE-BI can be extended for electrically large problems by the fast multipole method. An efficient preconditioner is constructed with both the finite-element matrix and the near-field part of the boundary integral equation operator for the FE-BI analysis. The numerical examples demonstrate that this preconditioner is efficient for electromagnetic scattering in the half space.
IET Microwaves Antennas & Propagation 04/2010; · 0.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The periodic half-width microstrip leaky wave antenna (MLWA) with a backward to forward scanning capability is presented in this paper. The proposed antenna consists of a series of half-width MLWA. The radiating periods place on the different sides of the transmission line. The radiating period works in cutoff region of the first higher order mode, the periodic construction radiates the slow wave out along the edge. The experimental results show the main lobe scans electronically and continuously from 149?? to 28?? in H-plane ( y - z plane) toward end fire (+ z direction) when the operating frequency increases from 4.2-.9 GHz.
IEEE Transactions on Antennas and Propagation 04/2010; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A quasi microstrip leaky-wave antenna (QMLWA) with a two-dimensional (2-D) beam-scanning capability is presented in this paper. QMLWA consists of two half-width microstrip leaky-wave antennas with a phase-shifter. This new type of microstrip leaky-wave antenna has the advantages of reducing size, 2-D beam-scanning and suppressing back lobes. The main lobe scanning in H-plane ( y - z plane) is achieved through varying the operating frequency. When the operating frequency increases from 4.4-6 GHz, the main lobe scans from 84deg to 26deg in H-plane continuously. The main lobe steers in quasi-E-plane with varying the phase difference between two half-width microstrip leaky-wave antennas. The lobe scans from 78deg to 103deg in quasi-E-plane at 5.4 GHz. The experimental results show this short QMLWA (about 2 wavelengths) leaks power effectively. The back lobe in H-plane of QMLWA is suppressed 13 dB as compared with the conventional whole width MLWA at 5.4 GHz as example. The H-plane radiation characteristics of QMLWA are mainly determined by the width s of half-width MLWA and the distance D between two half-width MLWA together. This size-reduced QMLWA is useful in the automotive radar system and air traffic control.
IEEE Transactions on Antennas and Propagation 03/2009; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In the paper, a new method based on the integral equation is presented for the solution of electromagnetic problems associated with complex-media bodies. The new method offers an important advantage that the difficulty in deriving the relevant dyadic Green's function is effectively addressed through reformatting the Maxwell equations and then constructing a pair of coupled equivalent polarized electric and magnetic flux densities. Using this method, only free-space Green's function is needed not matter what materials of the body are involved. Without any loss of generality, the method of moments combined with three-dimensional vector basis functions can be conventionally used to reduce the obtained integral equations into the corresponding matrix equations. In the end, the efficiency of the new method is demonstrated by a representative example of an antenna nearby a bi-isotropic material body.
Microwave Conference, 2008. APMC 2008. Asia-Pacific; 01/2009
-
[show abstract]
[hide abstract]
ABSTRACT: A new multiresolution (MR) preconditioner is presented in this paper, and it is combined with the multilevel fast multipole algorithm (MLFMA) for the analysis of electromagnetic scatters; Furthermore, the MR preconditioner is modified to be more effective by including a perturbation which is constructed from the principle value term of the magnetic field integral equation (MFIE) operator for solving the electric field integral equation (EFIE), and the modified MR preconditioner is named perturbed MR preconditioner. The MR preconditioner is a physics-based preconditioning scheme for the Method-of- Moments (MoM) methods, which is derives from the generation of a MR basis. And the MR basis functions are constructed as linear combinations of Rao-Wilton-Glisson (RWG) basis functions. Unlike other preconditioners, the perturbed MR preconditioner requires a low memory occupation and computational cost for its generation and application. The use of the perturbed MR preconditioner combined with the MLFMA can speeds up the convergence rate of the iterative solvers effectively.
Microwave and Millimeter Wave Technology, 2008. ICMMT 2008. International Conference on; 05/2008
-
[show abstract]
[hide abstract]
ABSTRACT: A new set of higher order hierarchical basis functions is proposed for expansion of the current in electrical field integral equations (EFIE) solved by multilevel fast multipole algorithm (MLFMA) for the cavity scattering problem. The hierarchical two-level spectral preconditioning technique is developed to solve EFIE with multiple right-hand sides arising in monostatic radar cross section (RCS) calculations. The sparse approximate inverse (SAI) preconditioner based on the higher order hierarchical basis functions is used to damp the high frequencies of the error and the low frequencies is eliminated by a spectral preconditioner in a two-level manner defined on the lower order basis functions. The spectral preconditioner is combined with SAI preconditioner to obtain a hierarchical two-level spectral preconditioner. This newly constructed hierarchical two-level spectral preconditioner is used to speed up the restarted GMRES iterative algorithm. Numerical experiments indicate that the new preconditioner is efficient for the MLFMA and can significantly reduce both the iteration number and computational time.
Microwave and Millimeter Wave Technology, 2008. ICMMT 2008. International Conference on; 05/2008
-
[show abstract]
[hide abstract]
ABSTRACT: A new dual band printed inverted-F antenna (PIFA) for the 1.8 GHz digital communication system (DCS) and 2.4 GHz wireless local area network (WLAN) application is presented. The proposed antenna is based on a conventional PIFA, where the shorting strip is modified into a meandering shape such that the antenna can have a double resonance. The antenna finds an impedance bandwidth of 10.85% and 3.61% for SlK-10 dB at 1.8 GHz and 2.45 GHz, respectively. The maximum antenna gains are 2.83 dBi and 3.31 dBi correspondingly.
Antennas and Propagation Conference, 2008. LAPC 2008. Loughborough; 04/2008
-
[show abstract]
[hide abstract]
ABSTRACT: A fixed-frequency dual-beam steering microstrip leaky-wave antenna is presented in this paper. A novel equation with finite-difference time-domain method is proposed to calculate the complex propagation constant of microstrip leaky-wave antenna. The microstrip leaky-wave antenna is excited by multiterminals. By control the novel feeding configuration, the microstrip leaky-wave antenna has the advantage of main lobe's dual-beam and steering at fixed-frequency. The main lobe steers from 41 to 63 for right beam and from 117 to 139 for left beam symmetrically when operating frequency fixes at 7 GHz. This new microstrip leaky-wave antenna can easily be used as collision avoidance or automobile radar system.
IEEE Transactions on Antennas and Propagation 02/2008; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new wideband planar inverted-F antenna (PIFA) is introduced. The proposed antenna is based on a simple PIFA, where the shorting strip is modified into a meandering shape such that the antenna can have wideband characteristics. The antenna finds an impedance bandwidth of 45.2% for S11 < -10 dB from 1.565 to 2.48 GHz which can cover the GPS, DCS, IMT-2000, 2.4 GHz WLAN applications. The maximum antenna gains are 1.68, 1.83, 1.90 and 1.78 dBi correspondingly.
Electronics Letters 02/2008; · 0.96 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A novel two-dimensional beam-scanning microstrip leaky-wave antenna (MLWA) is presented. The proposed antenna consists of two half-width MLWA with a phase-shifter. This new type of MLWA has the advantages of two-dimensional beam-scanning and suppressing back lobes. This reduced size MLWA is useful in automotive radar systems and air traffic control.
Electronics Letters 02/2008; · 0.96 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, several Krylov subspace iterative algorithms are proposed as the solvers for the unconditionally stable three-dimensional Crank-Nicolson finite-difference time- domain (3D CN-FDTD) method. To demonstrate features of this method, a resonant cavity is analyzed. Numerical results indicate that the GMRES method is the most efficient solver for the dielectric cavity. And while the time step size excessively larger than the Courant-Friedrich-Levy (CFL) limit, the CN-FDTD maintained accuracy compared with the exact solutions.
Microwave Conference, 2007. APMC 2007. Asia-Pacific; 01/2008
-
[show abstract]
[hide abstract]
ABSTRACT: A novel two-element fixed-frequency beam-scanning microstrip leaky wave antenna (MLWA) array is presented in this letter. By controlling the phase shifter, the mainlobe of the microstrip leaky wave antenna array is steered at the fixed frequency. The measured H-plane radiation patterns and the simulated results show that the mainlobe can be scanned from 41 $^{circ}$ to 62 $^{circ}$ continuously when the operating frequency fixes at 7 GHz. This new MLWA array can be used as a collision avoidance system or automotive radar system.
IEEE Antennas and Wireless Propagation Letters 01/2008; · 1.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new spectral two-step preconditioning of multilevel fast multipole algorithm (MLFMA) is proposed to solve large dense linear systems with multiple right-hand sides arising in monostatic radar cross section (RCS) calculations. The first system is solved with a deflated generalized minimal residual (GMRES) method and the eigenvector information is generated at the same time. Based on this eigenvector information, a spectral preconditioner is defined and combined with a previously constructed sparse approximate inverse (SAI) preconditioner in a two-step manner, resulting in the proposed spectral two-step preconditioner. Restarted GMRES with the newly constructed spectral two-step preconditioner is considered as the iterative method for solving subsequent systems and the MLFMA is used to speed up the matrix-vector product operations. Numerical experiments indicate that the new preconditioner is very effective with the MLFMA and can reduce both the iteration number and the computational time significantly.
IEEE Transactions on Antennas and Propagation 09/2007; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Elliptical helical antenna using parasitic helix to enhance the axial ratio (AR) bandwidth is presented. The parasitic wire increases the AR bandwidth (AR < 3 dB) from 13.6 to 25%, and enhances the directivity by 2 dB in the frequency band interested, while maintaining the simple single feeding system. The simulated results and experimental results including AR, impedance and radiation patterns are given, and some good agreements are observed.
IET Microwaves Antennas & Propagation 09/2007; · 0.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An unconditionally stable Crank-Nicolson finite-difference time-domain (CN-FDTD) algorithm is presented for three-dimensional microwave circuit analysis. First, Mur's first-order absorbing boundary condition is applied this CN-FDTD algorithm. A symmetric successive over relaxation-preconditioned biconjugate-gradient algorithm is also proposed to solve the large sparse matrix equation obtained in the CN-FDTD method. Resonant cavity and several planar microstrip circuits are presented to illustrate the versatility of this technique. Numerical results indicate that with a time-step size excessively larger than the Courant-Friedrich-Levy limit, the accuracy of CN-FDTD is still much higher than that of the alternating-direction implicit FDTD.
IET Microwaves Antennas & Propagation 09/2007; · 0.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A generalized volume integral equation method is formulated for electromagnetic scattering by arbitrarily shaped complex bodies with inhomogeneous bi-isotropy. Based on the volume equivalence principle, the integral equations are represented in terms of a pair of coupled bi-isotropic polarized volume electric and magnetic flux densities. Reduction of the integral equations into the corresponding matrix equations is obtained using the method of moments (MoM) combined with the tetrahedral mesh. In the MoM solution, the three-dimensional solenoidal function is incorporated as the basis function defined over each tetrahedral element and the details of implementation, particularly the treatment of integral singularities, will be elucidated. The efficiency and accuracy of the proposed method are validated by illustratively supported examples.
IEEE Transactions on Antennas and Propagation 08/2007; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A spiral antenna with a helix loaded is investigated in this paper. Through combining the spiral with a helix together, circular polarization can be achieved in dual bands. Since the helix is loaded in the lower part of the spiral, this technique doesn't increase the antenna's volume but at the same time introduces another CP band. The experimental result shows that the lower band and upper band are 4.0% and 62.07% respectively. The characteristics of impedance, current distribution and radiation pattern will also be presented. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1939–1942, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22596
Microwave and Optical Technology Letters 05/2007; 49(8):1939 - 1942. · 0.62 Impact Factor
