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Title: November 2006 Full Issue
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
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Title: A Hybrid Framework for Antenna/Platform Analysis
Abstract: Abstract − Hybrid combinations of numerical and asymptotic methods are utilized to evaluate in-situ antenna performance, and coupling to other systems on a shared platform such as a ship topside. This paper describes a combination of the finite element-boundary (FE-BI) method with ray techniques for evaluating antenna patterns in the presence of complex platforms. Specifically, a very complex array antenna may be modeled with FE-BI, and interfaced to the platform via the use of equivalent currents. For the case considered here, the FE-BI is accelerated with the array decomposition fast multipole method (AD-FMM) so that large arrays may be considered. A novel discrete Fourier transform method is also introduced to provide a greatly reduced representation of the fields over a planar array aperture and the uniform theory of diffraction (UTD) along with iterative physical optics (IPO) are used to characterize the platform. To tie it all together, a matrix framework is formulated to iteratively increment the higher order interactions between antennas and platform.
Author(s): R. J. Burkholder, P. H. Pathak, K. Sertel, R. J. Marhefka, J. L. Volakis , R. W. Kindt
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 2108 KB

Title: Low SAR Phased Antenna Array for Mobile Handsets
Abstract: Abstract—A two-element phased antenna array for a mobile handset is investigated using the Finite Difference Time Domain (FDTD) method. The array is designed to provide a spatial minimum in SAR in the near field zone inside the human head. The optimisation algorithms to obtain the minimum peak specific absorption rate (SAR) and minimum total absorbed power are addressed. It is found that these criteria are not seriously conflicting. The effects of the head-array spacing on the optimum array feeding voltages and the reduction in SAR are discussed. The results are compared with those from a normal single element handset, showing that the overall efficiency and azimuth coverage are improved and that peak specific absorption rate in the head can be reduced by at least 8 dB.
Author(s): J. Moustafa, N. J. McEwan, R. A. Abd-Alhameed, P. S. Excell
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 724 KB

Title: Numerical Simulation Approaches for Phased Array Design
Abstract: Abstract - This paper reviews the two well-known numerical simulation techniques that are widely used in antenna modeling; the finite-difference time-domain (FDTD) and the Method of Moments (MoM). The packages FDANT (prepared in Fortran language by using FDTD) and NEC2 (public domain code for the MoM) are used to model various types of antenna arrays, their advantages/disadvantages are discussed on characteristic design examples, and they are calibrated one against the other. Also, a simple Matlab package (ANTEN_GUI) for the visualization of radiation patterns, beam forming and beam steering capabilities of user-designed planar arrays of isotropic radiators (which can be used to test the above mentioned packages and as an educational tool, in e.g., antennas and propagation lectures) is introduced1.
Author(s): L. Sevgi
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 1360 KB

Title: Modeling Large Phased Array Antennas Using the Finite Difference Time Domain Method and the Characteristic Basis Function Approach
Abstract: Abstract −In this paper we describe an approach for solving large phased array problems, using the Characteristic Basis Function Method (CBFM) in conjunction with the Finite Difference Time Domain (FDTD) technique. The method is especially tailored for solving large arrays that may be covered with Frequency Selective Surfaces (FSSs). Several illustrative examples are provided and the results are validated for a number of test cases. This is accomplished by comparing the results derived by using the proposed technique with those obtained via a direct simulation of the entire array on a PC cluster. Of course, the direct problem places a heavy demand on the computer resources, especially as the problem size becomes large. In contrast to the direct method, the increases in the simulation time and the burden on the computer memory are incrementally small in the present approach, as the problem size is increased from moderate to large.
Author(s): Nader Farahat, Raj Mittra, Neng-Tien Huang
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 402 KB

Title: Direction of Arrival Estimation in a Multipath Environment: an Overview and a New Contribution
Abstract: Abstract — This paper proposes a new computationally efficient algorithm for direction-of-arrival (DOA) estimation in a multipath environment using a uniform linear array (ULA) of equispaced sensors. The paper starts by presenting a comprehensive overview of the classical MUSIC algorithm used for DOA estimation of uncorrelated signals. The effect of different factors related to the signal environment as well as the sensor array is investigated. The concept of spatial smoothing required in the case of correlated signals encountered in multipath propagation environments is then discussed. This then leads to the development of a new computationally efficient DOA estimation algorithm that is proposed for a multipath environment with unknown correlated signals. The algorithm comprises two stages: a first stage for discriminating uncorrelated signals, and a second stage for resolving the directions of arrival of correlated signals using covariance differencing and iterative spatial smoothing. Simulation results show that the proposed algorithm operates at a much lower computational cost compared to standard methods. The proposed algorithm also offers a hardware saving by reducing the number of sensors required to detect a given number of signals.
Author(s): Ebrahim M. Al-Ardi, Raed M. Shubair, Mohammed E. Al-Mualla
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 412 KB

Title: Polarization Isolation Characteristics Between Two Center-Feed Single-Layer Waveguide Arrays Arranged Side-by-Side
Abstract: Abstract - The near field coupling between two large alternating-phase fed single-layer waveguide arrays arranged side-by-side is analyzed by the Finite Element Method (FEM) (HFSS). First, the overall reflection as well as the radiation pattern from the array (320 slots and 18.4 λ x 14.9 λ) is analyzed, and excellent agreement with measurements is observed. Next, the isolation between two arrays is computed, and remarkable polarization isolations of more than 80 dB are predicted. The isolation is verified by measurements. The influence of the relative arrangement of the arrays upon the isolation is discussed.
Author(s): Yasuhiro Tsunemitsu, Jiro Hirokawa, Makoto Ando, Yohei Miura, Yasuhiro Kazama, Naohisa Goto
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 1538 KB

Title: Radiation by a Linear Array of Half-Width Leaky-Wave Antennas
Abstract: Abstract—Leaky-wave antennas are interesting apertures for a variety of applications due to their low profile and wide bandwidth. They are inherently traveling wave antennas, and hence are best suited for end-fire applications. A new type of leaky-wave antenna, the halfwidth leaky-wave antenna (HWLW), has been recently investigated and found to have similar radiation properties as its full-width leaky-wave (FWLW) counterpart, but only requiring half the transverse dimension. In addition, the feeding mechanism for a HWLW antenna is considerably simplified compared to the FWLW antenna. This paper discusses arraying these antennas to provide both increased gain and scanning capability. It will be seen that arraying HWLW antennas is more complex than its narrowband counterpart, the patch antenna.
Author(s): Daniel Killips, Joshua Radcliffe, Leo Kempel, Stephen Schneider
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 982 KB

Title: Macro-Scale Basis Functions for the Method of Moment Analysis of Large Periodic Microstrip Arrays
Abstract: Abstract – This paper presents a hybrid numericalasymptotic technique for the analysis of large periodic microstrip arrays. In the solution of a typical array problem, both macro-scale and element-scale spatial variations of the electromagnetic quantities are encountered. For large periodic arrays, the truncated periodicity induces a macro-scale behavior that is weakly dependent on the radiating elements themselves, but strongly dependent on the array periodicity and phasing. To incorporate this global phenomena, appropriate macro-scale functions are used in the framework of a method of moment solution. These macro-functions are associated to Floquet wave induced diffracted waves and guided waves, excited at the array boundary. The properties of these functions are discussed here. The technique is applied to the simple but significant case of printed dipole array, in order to demonstrate the effectiveness of the approach.
Author(s): A. Cucini, S. Maci
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 354 KB

Title: A Serial-Parallel FDTD Approach for Modeling the Coupling problem between Two Large Arrays
Abstract: Abstract −Solution of large problems using a numerically rigorous approach is always challenging because of the heavy burden they impose on the CPU. In this paper we introduce a new serial-parallel FDTD approach to solve large electromagnetic problems, e.g., coupling between two arrays separated by a large distance, that is difficult to handle via a direct application of the FDTD algorithm because of large size. This technique is based on dividing the original problem into relatively small sub-regions, and evaluating the solution that are localized in each of these sub-regions. The excitation of the sub-regions can either be direct sources, as for instance in the aggressor array, or be derived from the fields propagating into domain–from adjacent regions through the interfaces. We show that the results obtained by using the proposed approach compare well with the direct FDTD solution for some test problems, involving coupling between two phased arrays. Of course, the advantage of using the serial-parallel approach is that it can handle very large problems, well beyond the scope of the direct methods.
Author(s): R. Mittra, H. Abd-El-Raouf, N. Huang
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 846 KB

Title: Preconditioned GIFFT: A Fast MoM Solver for Large Arrays of Printed Antennas
Abstract: Abstract— A new type of fast method of moments (MoM) solution scheme using standard basis functions for large arrays with arbitrary contours and/or missing elements is applied to array antennas in a layered configuration. The efficiency of the method relies on use of the FFT along with approximating the Green’s function as a separable sum of interpolation functions defined on a relatively sparse, uniform grid. The method is ideally suited for solving array problems, and its effectiveness is demonstrated here for planar arrays of printed antennas. Both fill and solve times, as well as memory requirements, are dramatically improved with respect to standard MoM solvers.
Author(s): B. J. Fasenfest, F. Capolino, D. R. Wilton
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 398 KB

Title: Generalized Scattering Matrix (GSM) Approach for Multilayer Finite Array Analysis
Abstract: Abstract — The paper presents the Generalized Scattering Matrix (GSM) approach for analyzing multilayer printed array structures. The analysis involves computation of the overall GSM of an infinite array structure, Floquet modal based analysis of mutual coupling between array elements followed by estimation of finite array characteristics. A slot-fed patch array of 225 elements is used as an example for numerical results. It is found that the input match of the edge elements significantly differs from that of the elements in the center region of the array. The advantages and disadvantages of the approach are discussed at the end.
Author(s): A. Bhattacharyya
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 312 KB

Title: Modeling the RF Performance of a Small Array
Abstract: ABSTRACT - Large phased arrays can be reasonably accurately modelled in finite element programs, such as HFSS using an infinite array model of the embedded element. This approximation is not applicable to small arrays, where each element is in a different electromagnetic environment. Very small arrays of simple elements (of about 10 elements or less) can be modelled as a complete unit, but slightly larger or more complex arrays require additional techniques to be modelled accurately. The predicted performance of several versions of a small array has been compared using HFSS V9.5. The arrays contained either waveguide or printed dipole elements and, within the limits of available computing resources, solutions were generated for (1) complete array models, (2) half and quarter array models with symmetry planes, and (3) infinite array models.
Author(s): P. Foster, A. Wicks
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 366 KB

Title: A Critical Examination of Receive and Transmit Scan Element Pattern for Phased Arrays
Abstract: Abstract — The measurement of Scan Element Pattern by exciting only the center element is evaluated, both for gain at broadside and for behavior versus scan (normalized at broadside). A large dipole array of 50 × 50 elements is used in a 64 bit computer test bed, for calculations including mutual impedance. These results are compared with those where all elements are properly excited. A simple rigorous derivation of SEP including impedance mismatch is presented.
Author(s): R. C. Hansen
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 249 KB

Title: Modeling Conformal Array Antennas of Various Shapes Using Uniform Theory of Diffraction (UTD)
Abstract: Abstract - Traditionally, antennas have been designed as separate components, mounted on e.g. masts, buildings, and vehicles. Modern systems, however, require antennas to be integrated with existing structures. This paper discusses the analysis of conformally integrated array antennas using the hybrid UTD-MoM method, in particular arrays on doubly curved surfaces. Computed results are shown including singly and doubly curved surfaces. Most of the results are verified by measured results and calculated results obtained with a modal solution.
Author(s): P. Persson
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 491 KB

Title: Efficient Wideband Power Divider for Planar Antenna Arrays
Abstract: Abstract — Power dividers with a good match over a wideband of frequencies are designed using Klopfenstein impedance taper for use with wideband antenna arrays. To validate the proposed design procedure a 2-way stripline, and a 2-way microstrip power divider are designed, fabricated, and measured. The measured return loss reveals better than –24 dB (from 4.3 GHz to 19.5 GHz) match for the 2-way stripline, and –27 dB (from 2.2 GHz to 12 GHz) match for the 2-way microstrip. Then a single Klopfenstein taper is used in the design of a 4-way stripline power divider. Measurements reveal return loss better than –22 dB (from 2.3 GHz to 19 GHz) for the 4-way stripline power divider. Furthermore, use of a single taper resulted in a shorter feed network compared to the traditional 4-way feed network using 2-way power dividers at two stages.
Author(s): V. Demir, D. Elsherbeni, D. Kajfez, A. Z. Elsherbeni
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 359 KB

Title: Genetic Algorithm Applications for Phased Arrays
Abstract: Abstract—Analytical approaches to phased array optimization started in the mid 1940s and transitioned to numerical techniques that can find a local minimum. Computers spurred the development of many different local optimization algorithms that worked well for a few variables and a cost function with a single minimum. In the 1990s, the genetic algorithm (GA) emerged as a competent optimization algorithm for a wide range of complex cost functions. This paper reviews phased array optimization and lays the foundation for the use of the GA. An extensive reference list is provided and some future research areas are discussed.
Author(s): R. L. Haupt
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 340 KB

Title: Genetic Algorithm Optimization of a Traveling Wave Array of Longitudinal Slots in a Rectangular Waveguide
Abstract: Abstract — Genetic Algorithm is used to optimize the performance characteristics of a traveling wave array consisting of longitudinal slots cut in the broad wall of a rectangular waveguide. An analysis method employing a loaded transmission line to model the slot arrays is employed. External mutual coupling is considered. The self admittance of the radiating slots is computed using the method-of-moments technique applied to the pertinent integral equations. Numerical results indicate typical performance improvements possible using the genetic algorithm optimization.
Author(s): Anders Jensen, Sembiam R. Rengarajan
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 496 KB

Title: Approximate Compensation for Mutual Coupling in a Direct Data Domain Least Squares Approach using the In-situ Measured Element Patterns
Abstract: Abstract —This paper presents a new technique for an approximate compensation of the effects of mutual coupling among the elements of an array using the measured in-situ element patterns in a direct data domain least squares algorithm. In this paper, we consider the antenna elements in the phased array to have finite dimensions, i.e., they are not omni-directional radiators. Hence, the antenna elements sample and re-radiate the incident fields resulting in mutual coupling between the antenna elements. Mutual coupling not only destroys the linear wavefront assumption for the signal of interest but also for all the interferers impinging on the array. Thus, we propose a new direct data domain approach that partly compensates for effect of mutual coupling, specifically when the jammer strengths are comparable to that of the signal. For strong interferers, a more accurate compensation for the mutual coupling is necessary using the transformation matrix through the formation of a uniform liner virtual array.
Author(s): W. Choi, T. K. Sarkar, O. Allen, J. Asvestas
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 378 KB

Title: Multiple Beam Antenna Technology for Satellite Communications Payloads
Abstract: Abstract—This paper reviews multiple beam antenna (MBA) technologies that are applicable for satellite communications payloads. It provides design, performance analysis, and hardware implementation aspects of various types of MBAs that include reflector MBAs, phased array MBAs, and lens MBAs. Parametric design of these MBAs and RF analysis for coverage gain and inter-beam isolation are given. Recent advances and trends in MBA technologies for space applications are discussed.
Author(s): S. Rao, M. Tang, C. Hsu
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 1464 KB

Title: A Survey of Phased Arrays for Medical Applications
Abstract: Abstract—This paper presents a survey of phased arrays for a wide variety of medical applications. Medical imaging modalities including tomography, confocal imaging, thermography, and MRI are covered, as well as hyperthermia for treatment of cancer. Arrays include planar, cylindrical, and conformal configurations of many types of antennas including monopoles, dipoles, microstrips, horns, bowties, loops, etc.
Author(s): C. Furse
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 550 KB

Title: November 2006 Journal Front/Back Matter
Abstract:
Author(s):
File Type: Journal Paper
Issue:Volume: 21      Number: 3      Year: 2006
Download Link:Click here to download PDF     File Size: 512 KB