Shih-Chung Tuan

Transient Analysis of Scattering From a Perfectly Conducting Parabolic Reflector Illuminated by a Gaussian Beam Electromagnetic Field

In this paper we present a time domain (TD) transient analysis of electromagnetic (EM) fields scattered from a perfectly conducting parabolic reflector, when it is illuminated by EM fields of a general astigmatic Gaussian beam (GB). The analysis employs physical optics (PO) approximation and analytic time transform (ATT) to treat complex time delays that result from the GBs complex phase variations along its propagation axis in the frequency domain (FD). This work exhibits two advantages. First, within the validity of the paraxial approximation of the GB fields, this TD-PO quasi-analytic solution is highly efficient in reducing the numerical surface integration into a one-dimensional angular integration, which remains fairly independent of reflector sizes in most practical applications. Second, the nature of the PO approximation assists in avoiding ray-caustic problems encountered in most asymptotic solutions. Numerical examples are presented to illustrate the phenomena of GB scattering, as well as the uses of the described solution.

Analytic Analysis of Transient Scattering From a Finite Second-Order Surface Illuminated by an Incident Plane Wave

A closed-form analytic solution based on a time-domain (TD) physical optics (PO) approximation is developed for the scattering from a finite second-order surface when illuminated by a transient impulsive plane wave. This TD-PO solution can be applied via a convolution to derive the early time transient fields scattered from the same scatterer that is illuminated by a realistic astigmatic finite-energy pulse. The closed form TD-PO solution is obtained by inverting the corresponding frequency-domain PO solution into TD. This solution can be expressed in terms of reflection and diffraction components of the scattering mechanisms as in other conventional high-frequency asymptotic solutions. Numerical examples are presented to demonstrate its physical phenomenon of the scattering mechanisms

Analytic Analysis of Transient Radiation From Phased Array Antennas in the Near- and Far-Field Focus Applications

This paper presents an analytical transient analysis of electromagnetic field radiation from a time-delayed and finite periodic array of antennas for the near- and far-field focused applications. The elemental current moments of array are assumed with a transient impulse input for the excitations whose signals are delayed to radiate near-zone focused fields. The transient field phenomena for each of the Floquet mode expansion were analyzed. The solution reduces to the case of far-zone field radiation by moving the focus point to the far zone. The analysis shows that the radiation exhibits an impulse field at the focused point, and finite pulses at locations away from the focus point. Phenomena of partial cylindrical wave functions have been observed.

Analytic Transient Analysis of Radiation From Ellipsoidal Reflector Antennas for Impulse-Radiating Antennas Applications

A time-domain (TD) analysis of ellipsoidal reflector antennas is presented to predict the transient scattered fields when it is illuminated by a cosine-tapered and transient-step feed radiation whose phase center is located at the nearby focus. A transient-step function of the feeds radiation is considered because it will produce an impulsive response near the second focus of the reflector as interested in the applications of impulse-radiating antennas. This TD solution is in a closed form and remains valid both near and far from the reflector, and can be used via the convolution theorem to efficiently obtain the early time transient fields generated by the same ellipsoidal reflector antenna when it is illuminated by a realistic finite-energy pulse which emanates as a spherical wave from the focus. Numerical results are presented for the transient fields both near and far from the reflector.

An Analytic Solution of Transient Scattering From Perfectly Conducting Ellipsoidal Surfaces Illuminated by an Electromagnetic Plane Wave

This paper presents an analytical and closed-form solution, using a time domain (TD) physical optics (PO), for the fast analysis of transient scattering from a finite and perfectly conducting ellipsoidal surface when it is illuminated by a transient-step plane wave. The advantage of ellipsoidal shapes to resemble a variety of realistic surfaces such as spherical, parabolic or planar surfaces allows the developed solution applicable to model a realistic scattering object such as an aircraft in an effective fashion. Physical appealing interpretation of wave phenomena in terms of reflection and diffraction mechanisms is also provided in the solution. Numerical examples are presented to demonstrate its physical phenomena of scattering mechanisms.

Optimization of propagation models for the radio performance evaluation of wireless local area network

The wireless local area network (WLAN) has become very popular in recent years because of its utilization on free frequency bands and high speed of data transmission. However, due to increasing applications of wireless communications in these free bands, WLANs are facing interference from themselves and other applications, not only because the utilization of these free bands are very crowed, but also because most of the networks in these bands are not well planned. Optimizations of network planning are thus very important. Among the planning procedures, accurate propagation predictions are the most essential step. This paper optimizes the propagation models based on measurement techniques and employs the optimized models to evaluate the network performance of WLANs in an indoor environment where the WLAN is most popularly employed.

Applications of Shielding Techniques to Enhance the Antenna Performance of Mobile Communications and Reduce SAR Induction in the Human Head

Applications of shielding techniques are proposed to enhance the antenna performance of mobile communications. The shielding structures for the base station antennas are based on an implementation of resistive plates that tend to reflect the antenna radiation in the side lobes to main beam region, and hence optimize the overlapping coverage between sectors. On the other hand, magnetic materials are employed to design the shielding structures for handset antennas in order to provide good shielding effectiveness for magnetic near fields that were shown to be the major cause of a specific absorption rate (SAR) in the human head. Our studies show that with this shielding application the antenna performance can be enhanced while simultaneously reducing the SAR induction.

Floquet modes-based asymptotic analysis of scattering from FSS-type reflectarray/transmitarray for near-zone-focused radiations

This paper presents the asymptotic formulation of ray fields in the decomposition of electromagnetic (EM) scattering mechanisms from a one-dimensional, semi-infinite and periodic array when it is illuminated by a line source. This technique can be applied to analyze the passive FSS (frequency selective surface) type periodic structures with identical elements, or the reflectarray and transmitarray type antennas that are phased to radiate EM fields focused in the near zone of the array aperture. The solutions are built up based on the Floquet mode expansion of the scattering fields, and are obtained by asymptotically evaluating the resulted integrals to express the fields in terms of reflected/transmitted and edge diffracted fields as previously addressed in the framework of uniform geometrical theory of diffraction (UTD). The theoretical investigations over the scattering mechanisms and propagation phenomena are performed. Numerical examinations are presented to demonstrate the utilization of these solutions.

Investigation of electromagnetic interferences caused by the stacked I/O connectors

This paper presented the investigations of the electromagnetic interferences (EMI) caused by the noises resulted from a common mode of stacked I/O connectors, which are analyzed using both numerical simulations and experimental measurements. The structures of stacked I/O connectors popularly exist on the printed circuit board (PCB) of todays information technology equipments (ITE) for the purpose of reducing the sizes of equipments, from where it is observed that more size reduction will cause severer EMI. After the diagnosis and analysis, a strategy is presented to suppress the noise level as well as its emission, which is found to be very effective as shown in our examinations.

Analytical analysis of electromagnetic transient scattering from perfectly conducting ellipsoidal surfaces illuminated by a plane wave

A time domain (TD) analytical analysis of electromagnetic (EM) transient scattering from a perfectly conducting ellipsoidal-like surface with a finite edge contour is performed by using an approximation of TD physical optics (TD-PO). In particular, a closed-form solution has been developed in the case when the surface is illuminated by a transient-step plane wave. An ellipsoidal surface is selected in this study because it may resemble a variety of realistic surfaces such as spherical, parabolic or planar surfaces. The integration of these various finite ellipsoidal-like surfaces may be used to model a realistic scattering object such as an aircraft, which makes this solution very applicable to treat realistic problems in an effective fashion.