Mook-Seng Leong

Dual-polarized slot-coupled planar antenna with wide bandwidth

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 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.

Electromagnetic dyadic Green's function in cylindrically multilayered media

A spectral-domain dyadic Greens function for electromagnetic fields in cylindrically multilayered media with circular cross section is derived in terms of matrices of the cylindrical vector wave functions. Some useful concepts, such as the effective plane wave reflection and transmission coefficients, are extended in the present spectral domain eigenfunction expansion. The coupling coefficient matrices of the scattering dyadic Greens functions are given by applying the principle of scattering superposition. The general solution has been applied to the case of axial symmetry (n=0, n is eigenvalue parameter in /spl phi/ direction) where the scattering coefficients are decoupled between TM and TE waves. Two specific geometries, i.e., two- and three-layered media that are frequently employed to model the practical problems are considered in detail, and the coupling coefficient matrices of their dyadic Greens functions are given, respectively.

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 method for designing broad-band microstrip antennas in multilayered planar structures

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.

Novel design of broad-band stacked patch antenna

A novel broadband stacked E-shaped patch antenna is proposed in this paper. The proposed antenna has an input impedance bandwidth of about 38.41%, better than the conventional E-shaped microstrip patch antenna, which has an input impedance bandwidth of 33.8%. Through the use of the washer on the probe of the stacked patch antenna, the input impedance bandwidth is improved further to 44.9%. The radiation patterns are found to be relatively constant throughout the whole band. Comparisons of these antennas are presented in this paper.

A miniaturized dual-mode ring bandpass filter with a new perturbation

A miniaturized dual-mode ring bandpass filter at 1.45 GHz with a bandwidth of 6% is demonstrated. The perturbation of the dual modes is realized by a pair of local ground defects. The miniaturization is achieved by loading the peripheral of the ring with the butterfly radial stub structure. A 41% loading factor has been achieved using this method. The simulated and measured results are in good agreement.

Fast solution of mixed dielectric/conducting scattering problem using volume-surface adaptive Integral method

This paper presents the adaptive integral method utilized to solve scattering problems of mixed dielectric and conducting objects using volume-surface integral equation. The scattering problem is formulated using volume integral equation and surface integral equation for dielectric material object and conducting object, respectively. The combined field integral equation is formulated to treat closed conducting surfaces. The method of moments is applied to discretize the integral equations. The resultant matrix system is solved by an iterative solver where the adaptive integral method is employed to accelerate the matrix-vector multiplication. The block diagonal preconditioner is implemented to further accelerate the convergence of the present solution. Numerical results are presented to demonstrate the accuracy and efficiency of the technique.

Radio wave propagation along mixed paths through a four-layered model of rain forest: an analytic approach

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 Greens 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. The 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.

Further improvement for fast computation of mixed potential Green's functions for cylindrically stratified media

A method of fast computation of the mixed potential Greens functions (MPGFs) in spatial domain for cylindrically stratified media has been developed. Based on the convergence behavior of the MPGFs in spectral domain, the discrete complex image method (DCIM) and the extrapolation technique are employed to perform the inverse Fourier transform, which is different from that of planarly stratified media. In order to evaluate the summation of cylindrical eigenmode from order of negative infinity to order of positive infinity, the Greens functions in spectral domain are rearranged so that acceleration technique can be well applied to speed up the convergence of summation process. For the integral along the deformed Sommerfeld integral path with respect to k/sub z/, DCIM is used to speed up the computation. After the quasistatic components are completely subtracted from the spectral domain Greens functions, the inverse transform of the remaining parts has an approximated analytical form. The proposed method can be used to accurately and efficiently calculate the spatial domain MPGFs, which are useful for characterizing conformal patch structures mounted on cylindrically stratified media.

Microwave attenuation by realistically distorted raindrops: Part I. Theory

By using a new raindrop model developed earlier and applying the first-order perturbation-expansion technique, the effects of realistic and nonaxisymmetric distortion of varying raindrop shapes on microwave attenuation are re-investigated in this paper. Under the assumption of nonaxisymmetric raindrop scatterers, a system of general equations satisfied by the scattering and transmission coefficients of the electromagnetic (EM) fields are derived under the zeroth-order and the first order approximations. Both the horizontal and the vertical polarizations are discussed. The scattered and transmitted EM fields are obtained by means of expansion of spherical vector wave functions. Under the first-order perturbation approximation, the total cross section is calculated and discussed. Compared with the previous formulas presented for the axisymmetric raindrop scattering, the new results of total cross section obtained here consist of two additional terms resulting from the nonaxisymmetric distortion. These additional terms due to the raindrops nonaxisymmetry are represented analytically and discussed numerically. Part II of this paper will present an application of the analysis to the specific microwave attenuation due to rain in the moderate climatic region and in Singapores tropical region. >