Hsien-Kwei Ho

Implementation of a forward-backward procedure for the fast analysis of electromagnetic radiation/scattering from two-dimensional large phased arrays

Forward-backward method (FBM) was successfully developed for the analysis of electromagnetic radiation/scattering from one-dimensional (1-D) phased array in an efficiency appealing fashion. The FBM applications to treat 2-D array problems are developed in this paper. Acceleration algorithm, performing better than the novel spectrum acceleration algorithm used for 1-D FBM computation, is also developed for this 2-D FBM so the unique advantages of high efficiency and O(N/sub tot/) computational complexity as in the 1-D problems can be retained where N/sub tot/ is the total number of array element. Numerical examples are presented to demonstrate its validity.

A discrete-time uniform geometrical theory of diffraction for the fast transient analysis of scattering from curved wedges

In this paper a discrete time (DT) representation of Maxwells equations is employed to describe the time domain (TD) Maxwells equations in terms of matrix equations analogous to time harmonic Maxwells equations, which allows one to conveniently develop many TD solutions based on their frequency domain (FD) formulations. It was then employed to develop a TD version of the uniform geometrical theory of diffraction (UTD) (referred as DT-UTD) for the efficient electromagnetic transient analysis of scattering from perfectly conducting curved wedges. This DT-UTD retains the advantages of its corresponding FD UTD solution in several aspects including the form, ray physical picture and definitions of ray parameters. Furthermore, the transformation of the FD-UTD to the DT-UTD formulation can be easily achieved via a simple interpretation of notation. Numerical examples are presented to validate and illustrate the utilizations of this DT-UTD.

A hybrid discrete Fourier transform-moment method for the fast analysis of large rectangular phased arrays

The fast analysis of large antenna phased arrays remains an interesting and challenging problem. This paper presents an approach to accelerate the MOM by employing a DFT (discrete Fourier transform) representation for the unknowns of conventional MOM. Such an approach combining DFT with MOM is called DFT-MoM. The DFT-MoM employs the coefficients of the DFT representation as the new unknowns and solves for the DFT coefficients. The MOM unknowns are then obtained subsequently.

A generalized forward-backward method for the efficient analysis of large array problems

Development of novel analysis techniques to treat large array problems remains attractive due to the increasing need to employ very large array structures in practical applications. Recently, a forward-backward method (FBM), has been extended to treat large array problems; several unique advantages have been demonstrated. The previous approach of FBM requires monotonic variation on the array surface in order to set up a forward-backward procedure. This limitation is overcome by a generalization of FBM (GFBM) (see Pino, M.R. et al., 1999), which allows arbitrary array elements in general shapes. In contrast to the previous FBM (see Chou, H-T, IEE Proc.-Microw. Antennas Propag., vol.147, no.3, 2000) where the current computation sweeps cell by cell (each cell corresponding to a MoM basis of pulse function) in the forward or backward procedure, the GFBM sweeps the current computation element by element (corresponding to array elements). A simple MoM procedure with very few unknowns (usually only these unknowns to model three elements at most) is employed to obtain the forward current and its backward correction on the selected element. This modification allows arbitrary array elements to be treated accurately. Numerical results demonstrate its validity.

Radiation Discrepancy Analysis for Metallic Reflectarray Antennas With Random Manufacture Distortion at mmW Frequencies

This letter presents the numerical analysis of radiation discrepancy when metallic reflectarray antennas experience manufacturing distortion at millimeter waves (mmW). The small wavelength of mmW may transform a slight machining distortion into severe phase errors and, consequently, cause radiation distortion. A mathematical model was developed using a realistic example at 38 GHz to validate it. The probability density function of normal distribution is used to model the manufacture distortion. The impacts on the antenna characteristics, including the antenna directivities, levels of cross polarization, and sidelobes are numerically evaluated by using FEKO.

Sidelobe suppression of reflector antennas by embedding non-resonant periodic metal cells along the reflector edge boundary

This paper presents an useful technique to reduce the edge diffractions of reflector antennas to improve its radiation characteristics and antenna efficiency. In contrast to conventional design by synthesizing the reflector surfaces, the proposed method introduces periodic metal cells along the reflectors edge boundary to alter the phases of induced currents. Based on the optimization of the phases, the sidelobes of antenna radiations can be suppressed in the field regions of particular interest. In this paper, the non-resonant periodic cell structure is presented, and optimized by using Genetic algorithm (GA) to optimize the phases of edge current and its radiation efficiency.

Local Area Radiation Sidelobe Suppression of Reflector Antennas by Embedding Periodic Metallic Elements Along the Edge Boundary

This communication presents a simple and useful technique to suppress the radiation sidelobe levels (SLLs) of reflector antennas by embedding reflecting elements around the edge boundary. Due to the fact that sidelobes mainly arise from the edge diffractions, the reflecting elements can alter the phase distribution of induced currents along the edge boundary, and therefore reduce the sidelobes through the destructive cancellation of fields radiated from these elements. The desired phases are found through the implementation of pattern synthesis technique such as genetic algorithm to optimize the SLLs. This technique of edge current phase alternation may be employed, in conjunction with using a tapered feed radiation to illuminate the reflector, to control both amplitudes and phases of edge currents. Thus, the edge diffraction mechanism may be better controlled to optimize SLLs. In this communication, both resonant and nonresonant types of metallic elements are implemented and compared to illustrate their characteristics of radiations in SLL suppression. This technique is particularly useful to suppress the SLLs within a local angular region. Numerical results based on the method of moment analysis are presented to validate the feasibility.

Numerical estimation of electromagnetic backscattering from near-zone vehicles for the side-look vehicle-detection radar applications at millimeter waves

The development of vehicle-detection radar system has attracted much attention in recent years due to the increasing interest of smart car and traffic control applications [1, 2]. The success of such radar applications highly depend on reliable estimation of signal echo from the targets, which provide the information of target detection, vehicle identification, and the estimation of locations and speeds. In contrast to the conventional radar applications, where the targets are very far away from the antennas, the vehicles under detection are in the near zone. The detection highly depends on a proper use of antennas, in particular a proper radiation beamwidth for the target illumination. Since the radar detection is directly related to the electromagnetic (EM) backscattering, the estimation of various vehicles is apparently helpful to the radar system design. In this paper, we will present a full-wave numerical simulation over popular vehicle types including sedan and trucks, where the multi-level fast multipole method (MLFMM) of method of moment (MoM) is applied. The vehicles are assumed to be in the near zone of antennas, where the phased array antennas with various beamwidths are used to estimate the EM backscattering fields. To improve the detection accuracy, we also developed a moving signal average technique of signal estimation such that the influence of structure variation in a vehicle on the radar signals can be reduced. Thus in the presentation, the moving signal average method is also applied to the estimation of backscattering fields to exhibit their characteristics.

Design of metallic reflectarray antenna and its radiation discrepancy due to the manufacture distortion at mmW

This paper presents the numerical design of a metallic reflectarray antenna at millimeter waves and investigates the radiation discrepancy due to the manufacture distortion. The metallic elements are convex and exhibit linear phase variation with respect to its height and frequency, and may provide a broader bandwidth in the composition of reflectarray antenna. The antenna is investigated at mmW. The radiation discrepancy due to the manufacture distortion is also studied and presented in this paper.

A discrete-time UTD formulation for the transient analysis of scattering from curved wedges

A discrete-time (DT) UTD formulation is proposed. It utilizes a time discretization to represent the time variation by simple basis functions, which may transform the scalar time Maxwells equations into a set of matrix-type equations that are analog to the Maxwell equations of harmonic time dependence. As a result, the DT-UTD can be formulated from the FD-UTD via a simple notation transformation. The advantages are that it retains a form similar to FD solutions and translates the time convolutions into a simple matrix multiplication without going through complicate and difficult studies of special transition function behaviors. Numerical examples are presented to validate the DT-UTD solution.