Le-Wei Li

A broad-band dual-polarized microstrip patch antenna with aperture coupling

In this communication, a dual-polarized aperture-coupled microstrip patch antenna with a broad-bandwidth high-isolation low cross-polarization levels, and low-backward radiation levels is designed and its features are presented. For broad bandwidth and easy integration with active circuits, it uses the aperture-coupled stacked patches. The corner feeding of square microstrip patches is applied and the coupling aperture is the H-shaped aperture. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. A dual-polarized antenna is designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of over 24.4% and the isolation is better than 30 dB over the bandwidth. 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 for S parameters and radiation patterns are presented and discussed.

A Broadband and High Gain Metamaterial Microstrip Antenna

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.

A coupled efficient and systematic full-wave time-domain macromodeling and circuit Simulation method for signal integrity analysis of high-speed interconnects

This paper presents an accurate and systematic approach for analysis of the signal integrity of the high-speed interconnects, which couples the full-wave finite difference time domain (FDTD) method with scattering (S) parameter based macromodeling by using rational function approximation and the circuit simulator. Firstly, the full-wave FDTD method is applied to characterize the interconnect subsystems, which is dedicated to extract the S parameters of the subnetwork consisting of interconnects with fairly complex geometry. Once the frequency-domain discrete data of the S parameters of the interconnect subnetwork is constructed, the rational function approximation is carried out to establish the macromodel of the interconnect subnetwork by employing the vector fitting method, which provides a more robust and accurate solution for the overall problem. Finally, the analysis of the signal integrity of the hybrid circuit can be fulfilled by using the S parameters based macromodel synthesis and simulation program with integrated circuits emphasis (SPICE) circuit simulator. Numerical experiments demonstrate that the proposed approach is accurate and efficient to address the hybrid electromagnetic (interconnect part) and circuit problems, in which the electromagnetic field effects are fully considered and the strength of SPICE circuit simulator is also exploited.

A fast volume-surface integral equation solver for scattering from composite conducting-dielectric objects

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.

A fast analysis of scattering and radiation of large microstrip antenna arrays

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.

A fast combined field volume integral equation solution to EM scattering by 3-D dielectric objects of arbitrary permittivity and permeability

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 of O(N) and a computational complexity of O(NlogN) respectively, where N denotes the number of unknowns

A Complete Set of Spatial-Domain Dyadic Green's Function Components for Cylindrically Stratified Media in Fast Computational Form

Numerical characterization of electromagnetic waves in cylindrically multilayered structures can be efficiently and rigorously performed by employing the method of moments (MoM) in spatial-domain. Thus the idea of obtaining spatial-domain Greens functions in closed form or fast computational form was proposed [1] and since then many useful results were obtained for planar layered media. For cylindrically layered media, the closed form Greens functions in spatial-domain were reported in [2], where the spatial-domain Greens function components due to z- and ø-oriented electrical and magnetic sources have been obtained using the generalized pencil of function (GPOF) method. This paper, as a further extension, presents spatial-domain Greens function components in fast computational form due to ρ-oriented electrical source embedded in cylindrically layered media. The Greens function components in approximate but fast computational form are compared with the exact Greens function components obtained from direct numerical evaluations of the corresponding integrals, and a good agreement between the fast computational form and the exact form. Furthermore, the spatial-domain Greens function components due to z- and ø-oriented electrical and magnetic sources have also been obtained but for all the possible azimuth angles.

Surface polaritons of small coated cylinders illuminated by normal incident TM and TE plane waves.

The surface polariton properties of TM or TE plane wave scattered by a coated cylinder are investigated in this paper. The coated cylinder (whose outer radius is much smaller than the wavelength) is assumed to be electrically small and low dissipative. Analytical formulas of the plasmonic resonances are derived and found to agree well with those obtained from exact expressions in the classical scattering theory. The behaviors of the scattering coefficients at resonances are also discussed and compared for different cases. While a single cylinder has the resonance at the relative permittivity of epsilon(r) = -1 (or relative permeability of mu(r) = -1) for the TE (or TM) polarization, the resonances of the coated cylinders change with different n values (where n denotes the series term or mode of the field), and also the inner and outer radii. It is shown that the scattered field in the near zone can be enhanced significantly compared to the incident wave. For the TE incident case, we take a silver coated nano-cylinder as an example to illuminate the near-field optical effect. Also, we have studied the peak values of the nth order scattered field for different n values and electrical parameter k0b (where k0 is the wavenumber of the free space and b denotes the outer radius of the cylinder) around the cylinder. The derived new formulas for total cross sections are given and they may provide us with some potential photonic applications such as surface cleaning and etching.

A Comparative Study of Radio Wave Propagation Over the Earth Due to a Vertical Electric Dipole

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 rho-1/2 in the rho direction as expected. However, the lateral wave given by does not exhibit rho-2 decay in the rho 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.

3D TSV transformer design for DC-DC/AC-DC converter

This paper presents a new concept of 3D transformer structure realized by through silicon via (TSV) technology. A set of different turn ratio transformers have been designed and analyzed. The results show that the proposed 3D TSV transformer possesses good performance with small size. Finally, an AC to DC converter circuit which based on proposed transformer has been designed. The result demonstrates that proposed 3D TSV transformer is suitable for AC to DC converter design.