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A miniaturized dual-band power divider for microwave frequencies has been developed. The present design utilizes the two-section impedance transformers implemented by the conjugately characteristic-impedance transmission lines (CCITL) to obtain size reduction with dual-band characteristic. The properly designed CCITL can achieve shorter electrical length than the normal transmission line (TL) to provide the same impedance transformation characteristic. Approximately one-fourth size reduction has been achieved by the proposed technique with reasonable results of scattering parameters, as compared with the similar design using the two-section impedance transformers but realized by the normal TLs.

A uniform geometrical theory of diffraction (UTD) ray analysis of a 60-GHz compact-range Gigabit wireless access system in the presence of the platform and human body is presented in this paper. The field radiated by a large array antenna, which is the source of the system, is represented by a collective UTD solution consisting of just a few rays emanating from specific points in the interior and on the array aperture boundary. These UTD rays can be interpreted as the Floquet waves and their diffractions at the edges and corners of the array boundary. They are traced to interact with the platform and human body based on the UTD method for predicting scattering effects. Numerical results are presented to show the efficacy of the present UTD approach for analyzing the system.

A broadband low-noise amplifier has been developed for an active digital TV antenna to operate in the frequency range of 470 - 800 MHz in the UHF band. The amplifier employs a SiGe:C Heterojunction Bipolar Transistor (HBT) and uses shunt negative feedback to achieve relatively flat gain and low return loss over a broad bandwidth. The amplifier prototype is fabricated on the 0.4-mm FR4 substrate. The measured results show that the gain of about 24 dB, the input return loss of better than 11 dB, and the noise figure of less than 1.4 dB are achieved throughout the desired frequency band.

This paper presents the development of a flexible printed active antenna for the digital television (DTV) reception in areas having poor signal or in high-rise buildings. The antenna structure is composed of a meander line printed on a polyimide film as a radiating element. It has a thickness of 0.3 mm, highly flexible, and very lightweight. The design and analysis of the radiating element are based on a full-wave method implemented by a commercial electromagnetic simulation software. The amplifier circuit consisting of a surface-mount transistor and passive components are integrated directly on the polyimide film, residing next to the feedline, to improve the antenna performance and minimize the whole antenna dimension. The impedance matching between the radiating element, the feed line, and the active circuit are considered. The measured results show that the return loss of more than approximately 10 dB, the maximum gain of about 18 dB, and the Omni-directional radiation pattern are achieved in the operating frequency band of 510–790 MHz. Due to its flexibility, low profile, lightweight, and additional gain, the proposed antenna could be useful for various specific applications.

In this paper, the computational modeling of the 2D human breast in hyperthermia treatment at 2.45 GHz is studied. The mathematical tool used in this study for investigating the distribution of generated heat is the COMSOL software where the breast is modeled by Pennes' bioheat equation. The model simulation is conducted to investigate the effects of exposure time and power inputs on the cancerous tissue temperature field. The results show that this method can cure the breast cancer patient without damaging the breast tissue.

A flexible printed antenna has been developed for digital television (DTV) reception. The antenna is a meander line printed on a polyimide film. It is extremely thin, flexible, compact, and very light weighted. The antenna is designed to operate in the UHF band with a relatively broad bandwidth covering the DTV broadcast frequency in Thailand. Due to its thinness and flexibility, the antenna is suitable for being integrated in a television set, conformally mounted on a wall or window, laminated within a glass window, etc. A prototype antenna has been built and tested. Measurement results are shown in this paper.

This paper presents the miniaturization of a three-port power divider for microwave frequency. The size reduction is achieved by the use of a quarter-wave-like transformer (QWLT) implemented by a properly designed conjugately characteristic-impedance transmission line (CCITL). The QWLT has a significantly shorter physical length than the conventional quarter-wave transformer (QWT). A novel condition for the isolation impedance has been derived and presented in this paper. The size reduction of the power divider can consequently reduce the whole dimension of the circuit composing the divider with insignificant performance degradation, and thus decreasing the manufacturing cost.

A uniform geometrical theory of diffraction (UTD) ray solution has been developed for describing the radiation fields produced by a linear antenna array which is conformal to a cylindrical conducting structure. The fields are described collectively in terms of just a few rays which are launched from a specific critical point in the interior and from the two end points of the linear array. Numerical results are presented to demonstrate the validity and efficiency of the present collective UTD ray solution.

Some word lists have been generated with various purposes to meet the target goals market and serve needs. This research proposes the framework for analyzing high frequency of words to create a word list for academic purposes, especially in Information and Communication Technologies (ICT). All resource words in this research are collected from journal articles in ICT. To evaluate the performance of this framework, the created word list from the framework is compared to other existing word lists. The results of this study are beneficial, but not limited, to ICT students, English language students, English language instructors, and ICT instructors.

In this paper, an analysis of maritime communications between a ship at sea and a shore station using a ray-based Monte Carlo method has been proposed. A sea surface is modeled by the one-side Pierson-Moskowitz spectrum. A Monte Carlo method based on a ray tracing is employed to predict the scattering from the temporally evolving rough sea surface for each time step. The maximum of double reflections is restricted in the ray tracing for a practical purpose. The total received signal is the superposition of the direct propagating field and the scattered field by the sea surface. The statistical numerical result is finally obtained by averaging the results from many realizations. Numerical results for the link performance evaluation obtained by the proposed method are illustrated. The results show that the misalignment of transmitting and receiving antennas due to the rolling ship has relatively less impact on the communication link performance than the multipath fading due to the scattering by the temporally evolving rough sea surface.

An empirical formulation for the estimation of mutual coupling between elements in a microstrip patch array has been proposed. The formulation is expressed in closed form in terms of simple functions of element spacing and azimuthal angular separation between elements. The least square method is used to evaluate the mutual impedance values computed by the proposed formulations with sample data obtained by numerical simulation to determine the coefficients in the formulations. The formulation can be used to estimate the mutual coupling between any elements in the same array within certain ranges of element spacing and azimuthal angular separation. The validity and accuracy of the proposed formulation is examined and illustrated by numerical results.

A microstrip antenna has been developed for being integrated into a television (TV) set for digital television (DTV) reception. The proposed antenna is a meander line antenna printed on an FR-4 substrate. It has a compact size, low-profile, and light weight. The antenna has a broad bandwidth in the UHF band allocated for DTV broadcast in Thailand. A prototype antenna was built and installed as a built-in antenna in an LED television which is relatively thin and thus suitable for wallmounted installation. A television with a built-in antenna does not requires an external antenna thus providing low-profile design and the ease of installation. This work can lead to an innovation in the television and antenna industries in the future.

A discrete Fourier transform (DFT)-based asymptotic high-frequency, uniform geometrical theory of diffraction (UTD) ray solution is developed to describe, in closed form, the collective field produced by large finite phased arrays of printed antenna elements on a grounded material substrate. Such a DFT-UTD ray analysis yields useful physical insights into the large array radiation and scattering mechanisms. This is in contrast to the conventional array element-by-element summation for the radiated field which lacks the above useful properties. In the present work, any realistic arbitrary array current distribution, i.e., in the presence of array mutual coupling, is represented by a DFT expansion so that each term in the expansion becomes a simple uniform array distribution with a linear phase, which then directly facilitates the development of the asymptotic UTD ray solution. Furthermore, another significant advantage of the DFT is that for most practical array excitations, only a relatively few DFT terms remain dominant in the expansion and are sufficient to provide reasonably accurate results. Some numerical examples are presented to illustrate the utility of this collective DFT-based asymptotic UTD ray solution for large array fields.

A novel approach which utilizes a discrete Fourier transform (DFT)-based preconditioner in an iterative moment method (MoM) solution of the governing integral equation for the electromagnetic (EM) problems of the radiation and scattering from large finite periodic antenna arrays is presented. The preconditioner is primarily constructed via the block-diagonal approximation of the transformed impedance matrix in the DFT domain, in which that matrix becomes sparse and nearly diagonal due to the properties of the DFT basis functions. The preconditioner in the original spatial domain is simply obtained by the inverse DFT. This preconditioner is shown to significantly improve the convergence rate of the iterative solution. Moreover, it is rather simple to implement and requires relatively small extra computational cost. The performance of the present approach is illustrated through numerical results.

In this paper, we present an optimization study on multi-section dipole antenna designs for printed UHF RFID, in which the antenna structure is divided into several unequal sections of radiating areas. The optimization work is extensively performed on the thickness, the length, as well as the width of each section in order to obtain optimal-performance multi-section printed dipole antennas at the lowest possible cost. The simulation results illustrate that a four-section dipole antenna structure with each succeeding section having the width approximately equal to half the width of its prior section achieves superior antenna efficiency performance. The conductive ink consumption of this antenna design is reduced around 51% when compared with the conventional flat layer design in order to achieve the same level of antenna efficiency performance as the ideal copper-trace dipole antenna.

A uniform geometrical theory of diffraction (UTD) ray solution is obtained for describing the surface fields produced by an aperture formed by a large phased array antenna mounted conformally on a locally convex, but otherwise relatively arbitrary large metallic platform. The electromagnetic equivalence theorem is employed to obtain the equivalent sources over the array aperture. The fields on the same convex surface produced by these equivalent sources are represented collectively by the present UTD solution in terms of just a few rays emanating from specific points on the edges and the corners of the array aperture boundary. These surface rays once launched from the array aperture then interact with the rest of the platform via the UTD method. This UTD solution can be used to efficiently calculate mutual coupling between two conformal array antennas installed on the same platform.

This paper presents a hybrid combination of the generalized ray expansion (GRE) method and high-frequency methods for analyzing the scattering and radiation problems incorporating electrically large and complex structures. A dense grid of ray tubes are launched from the phase centers of the subapertures making up the equivalent surface which encloses the target in the scattering problem, or the antenna in the radiation problem. Those rays represent the equivalent incident field on the target in the former case, and the field radiated by the antenna in the latter case. The rays are then traced through interactions with the target or the nearby structure based on high-frequency methods. The main advantage of the GRE method is that only one set of rays needs to be traced and it is independent of the excitation.

The generalized ray expansion (GRE) method was originally developed for analyzing high-frequency scattering from the interior of cavities [1],[2]. We propose to combine it with physical optics (PO) to reduce the effort of the initial ray tracing of incident field for efficiently modeling scattering from electrically large and complex targets of general shape. The target is enclosed with a fictitious box which can be rectangular or spherical in shape (see Figure 1). The surface of the box is sub-divided into sub-apertures. Rays are launched from the phase centre of each sub-aperture to the target. Unlike the GRE used for cavity scattering, the rays are limited to the angle subtended by the target and the phase centre. The subsequent ray tracing from one part of the target to another part of the target follows the usual method in PO.

An efficient approach based on a hybrid combination of numerical and uniform geometrical theory of diffraction (UTD) methods for predicting the mutual coupling between conformal array antennas on a complex and electrically large metallic platform, such as an aircraft fuselage, is presented. The local fields are first obtained only within each individual array aperture by using numerical methods. Then the mutual coupling between arrays is computed by using the UTD ray method after the array aperture is decomposed into a relatively small set of subapertures. The UTD surface ray is launched from a single point located within each subaperture to couple to another array on the same platform.

An efficient approach based on a hybrid combination of numerical and uniform geometrical theory of diffraction (UTD) methods is developed to predict the performance of large conformal array antennas on a locally convex portion of an otherwise complex and electrically large metallic platform. The metallic platform is assumed to be modeled by a perfect electric conductor (PEC). Such conformal array antennas may either be a simple slot array in a convex PEC surface, or be an array of complex antenna elements slightly recessed in a cavity structure just below the skin line of a convex PEC boundary, and covered by a flush-mounted radome. Electrically large complex platforms comprising of a locally convex portion could be an aircraft, a spacecraft, an unmanned aerial vehicle (UAV), etc.

[1] A boundary diffraction wave (BDW) formulation is developed for predicting the collective radiation from large finite planar phased array antennas in a relatively efficient manner. This collective radiation is described in terms of a set of Floquet waves (FWs) arising from the array interior, together with the diffraction of these FWs by the finite array element truncation boundary; the latter is represented by a line integral of the incremental diffracted field over this boundary. In general, the BDW line integral must be evaluated numerically. The current distribution over the whole array is first obtained, for a given excitation, by full wave numerical methods. A traveling wave expansion is employed to represent the array distribution so as to facilitate the development of the BDW solution for arrays. Some numerical results based on the BDW are presented to demonstrate the utility and accuracy of the method for analyzing large planar arrays.

A relatively fast and efficient preconditioned iterative method of moments solution is developed for solving an integral equation governing the array element currents on large, planar, periodic arrays of printed elements/slots in a grounded multilayered medium. This solution is highly suitable for calculations on a personal computer (PC). The large finite arrays are assumed to be embedded in a grounded multilayered medium of infinite extent. Hence, a Green's function for the latter geometry is utilized as the kernel of the governing array integral equation to restrict the number of unknowns to be solved to only the element currents; this Green's function is evaluated asymptotically in closed form for source and observation points which are separated laterally over a distance of one free space wavelength or larger. The latter provides an additional, significant speed up of this solution. Also, a ray method is developed to rapidly evaluate the fields radiated/scattered by the array currents found via the above numerical method of moments solution of the corresponding array radiation/transmitting or scattering/receiving problem. These ray fields describe the collective radiation / scattering from the whole array at once, and provide a physical picture for the array radiation /scattering. Next, a hybrid combination of ray and method of moments is developed to drastically reduce the number of unknowns to be solved as compared to the conventional method of moments. The moment method matrix equation can be treated by a direct solver in this hybrid approach because of the presence of the relatively very few unknowns (of the order of hundred) irrespective of the array size. This is in contrast to the iterative solver for the array currents based on the preconditioned moment method approach mentioned in the beginning, which solves for the conventional number of unknowns (that are greater than or equal to the number of array elements; e.g. the number of unknowns in the iterative approach is of the order of hundreds of thousands for an array of tens of thousands of elements, as compared to only in the hundreds for the hybrid direct solver approach). Finally, the ideas which are developed and utilized in the hybrid ray-numerical approach for large planar arrays are significantly modified and extended to potentially treat realistic doubly curved large finite conformal arrays of complex elements embedded in multilayered media, including a radome that is flush with the skin line of an even larger metallic platform (such as an aircraft) in which the array is placed. Numerical results will be presented to illustrate the accuracy of all the above approaches.

Two efficient high-frequency (HF) methods, namely, a uniform geometrical theory of diffraction (UTD) and a boundary diffraction wave (BDW) method, for predicting the collective radiation from large finite planar antenna phased arrays are reviewed. The current distribution over the whole array for a given excitation is first obtained from a moment method (MoM) solution of the governing array integral equation. A traveling wave (TW) basis set is then used to represent the MoM based array distribution to facilitate an asymptotic HF analysis based on the UTD and BDW, respectively, to predict the "collective" radiation (or scattering) from the whole array at once. An asymptotic reduction of the BDW leads to the UTD. Both the UTD and BDW solutions provide a physical picture for the array radiation mechanisms.

A collective description of the radiation fields, as well as surface fields, that are excited by a large array conformal to a very large smooth, arbitrary convex metallic surface is obtained in terms of just a few uniform geometrical theory of diffraction (UTD) rays emanating from some interior and boundary points on the entire array aperture. The present solution provides efficient representation of the array fields, as well as useful physical insights into the array radiation and surface fields excitation mechanisms.

In this paper, a new and improved traveling wave (TW) expansion is introduced for the efficient uniform geometrical theory of diffraction (UTD) analysis of the collective radiation from large finite planar arrays. The array distribution which can be obtained by using the method of moments (MoM) solution of the governing array integral equation was represented, in the recent past, in terms of a discrete Fourier transform (DFT) based TW expansion because it was found to be highly compact. The DFT is superseded in this paper by the new TW expansion in which a highly compact sequence of TWs adequately represents the array distribution. It is seen that the TW expansion requires a total number of terms which are typically less than 1% of the total number of array elements, which is far less than the required DFT terms for the same accuracy.

A number of techniques and algorithms have been developed in the literature to reduce the computational time and also to overcome the memory storage limitations for solving large problems. In this work, a hybrid DFT-MoM approach has been developed to reduce the number of unknowns in the treatment of large finite arrays by using the DFT for representing the global array distribution. Due to the compactness of the DFT spectrum of global array current distribution for most typical array excitations, the number of unknowns can be reduced; hence reducing the computational time and memory storage requirements for the analysis of large finite arrays.

The problem of electromagnetic radiation and receiving by large finite periodic microstrip patch antenna arrays on a grounded slab together with a feed network is analyzed. In general, the more the number of elements in an antenna array, the larger the size of the corresponding feed network and the more computational resources required to solve this problem using full-wave or MoM analysis. Furthermore, since feed networks have to be designed such that they can operate well with corresponding antenna arrays in order to achieve desirable performance, in most cases their design process may require many iterations, which can result in a highly inefficient and time-consuming process and can be intractable for large antenna arrays. To improve the efficiency of the analysis of such problems, an approximate hybrid method is developed; it decomposes the problem into two major parts, one dealing with antenna arrays alone and the other dealing with feed networks alone; then, a generalized Thevenin's theorem is applied to combine the two parts systematically. The approximation in this hybrid approach results from the circuit solver that does not provide any contribution to the radiation by the feed lines. It is assumed that the feed lines are designed so that their radiation is negligible.

The DFT-based approximate of the impedance matrix is employed as a preconditioner in the iterative method to provide an efficient and accurate solution of integral equations for solving electromagnetic scattering and radiation problems of large finite periodic antenna arrays in grounded layered media. The DFT-based preconditioner is shown to effectively improve the convergence of the iterative solutions. The complexity of the preconditioner implementation is O(KlogK) in computational cost and O(K) in memory requirement for problem size of O(K).

The presence of surface waves different from the conventional grounded dielectric substrate surface wave modes, which can be excited on a finite periodic radiating array of printed dipoles, at frequencies for which the spacing between dipoles is typically less than half a wavelength is studied. The effects of such array guided surface waves on the array radiation characteristics are investigated. Techniques to suppress these surface waves are also discussed.

Munk et al. (2002) and Janning et al. (2002) have demonstrated the excitation of surface waves, which can exist under certain conditions, on a planar periodic finite /spl times/ infinite planar array of dipoles in free space when a plane wave is incident on the array. In this paper, the above work is extended to study the excitation of such surface waves on a completely finite, or finite /spl times/ finite, planar rectangular array of dipoles which is excited by an external plane wave. It is noted that these surface waves are guided by the perfectly conducting dipole elements of the array, and they should be distinguished from the more conventional surface waves of a printed dipole array on a grounded substrate which essentially correspond to the modes of the grounded substrate. Here, such surface waves are clearly isolated via a numerical moment method (MoM) solution of an exact governing array integral equation for the element currents. It is interesting to note that most array designs keep the array interelement spacing small enough to avoid the excitation of array grating lobes; it is precisely for such spacings that the present surface waves can be excited.

The radar scattering from 2D and 3D targets on a rough sea surface is investigated using computational techniques developed specifically for this problem. Numerical simulations and Monte Carlo studies yield insight into the scatter phenomenology. It is found that the scattering from a target on a random rough sea surface becomes more coherent as the incident field becomes more coherent, ie, for low wind speeds or low elevation angles. For the less coherent case, the average. and peak scattering levels of a target on a rough surface may be significantly higher or lower than for a flat surface, depending on the target geometry. A tilted plan model is proposed for predicting the variations in the RCS of a target on a rough sea surface by mounting the target on a locally planar surface which can tilt, similar to the two-scale composite model of ocean scattering. It is found that tilting the plane, or equivalent, rolling the target on a horizontal plane fields as much or more variation in the RCS than caused by the rough surface. However, the cross polarization introduced by the rough surface in 3D is not well predicted by the tilted plane model, nor is the unexplained behavior near the Brewster angle for vertical polarization.

A hybrid method, which combines the UTD ray technique with the numerical MoM approach was introduced to provide a relatively efficient analysis of the EM radiation/scattering from an electrically large, planar, periodic, finite array (see Aydin Civi, O. et al., Radio Science, vol.35, no.2, p.607-20, 2000). That hybrid approach is extended to deal with arrays on grounded dielectric slabs. This work is of interest in the analysis of many practical arrays such as dielectric covered slot arrays, printed dipole and microstrip patch arrays, etc. It is well known that surface waves which are present in the grounded dielectric slabs can affect array mutual coupling, and can lead to effects of scan blindness in such arrays.