Electromagnetic modeling and analysis of wireless communication antennas

The goal of this article is threefold: to present the basic principles of the application of method of moments (MoM), finite-difference time-domain (FDTD) and finite-element method (FEM) to analysis of antennas; to present examples of antenna simulations that show the capabilities of some modern commercially available simulators; to discuss future trends in modeling and analysis of microwave and millimeter-wave antennas for wireless communications.     

The application of scalable distributed memory computers to the finite element modeling of electromagnetic scattering

Large-scale parallel computation can be an enabling resource in many areas of engineering and science if the parallel simulation algorithm attains an appreciable fraction of the machine peak performance, and if undue cost in porting the code or in developing the code for the parallel machine is not incurred. The issue of code parallelization is especially significant when considering unstructured mesh simulations. The unstructured mesh models considered in this paper result from a finite element simulation of electromagnetic fields scattered from geometrically complex objects (either penetrable or impenetrable.) The unstructured mesh must be distributed among the processors, as must the resultant sparse system of linear equations. Since a distributed memory architecture does not allow direct access to the irregularly distributed unstructured mesh and sparse matrix data, partitioning algorithms not needed in the sequential software have traditionally been used to efficiently spread the data among the processors. This paper presents a new method for simulating electromagnetic fields scattered from complex objects; namely, an unstructured finite element code that does not use traditional mesh partitioning algorithms. © 1998 This paper was produced under the auspices of the U.S. Government and it is therfore not subject to copyright in the U.S.     

Seasonal prevalence of Vibrio species in retail shrimps with an emphasis on Vibrio parahaemolyticus

Seasonal prevalence of Vibrio species in shrimp samples from retail outlets in the South-western part of Iran was studied. A total of 300 samples were analyzed (75 samples in each season). Special attention was paid to the prevalence of total and pathogenic Vibrio parahaemolyticus. All the TCBS isolates were first identified to the genus level with PCR and then identified to the species level using a battery of biochemical reactions and tests. To investigate the pathogenicity of the isolated V. parahaemolyticus, multiplex PCR (tl, tdh and trh genes) was performed. Vibrios were detected during the whole investigation period, depending on the sampling season. They were detected in 18.6% of the winter samples, 64% of the spring samples, 70.6% of the summer samples and 41.3% of the autumn samples. Vibrio calviensis and Vibrio alginolyticus were dominant in samples of different seasons, with the average prevalence of 18.6% and 17.6%, respectively. V. parahaemolyticus was found in 4.0% of the winter samples, 13.3% of the spring samples, 18.6% of the summer samples and 8% of the autumn samples. During the period of this study, two tdh-positive strains were isolated, while no trh-positive V. parahaemolyticus strain was detected in samples of different seasons.     

A satellite-tracking K- and Ka-band mobile vehicleantenna system

This paper describes the development of the K- and K_a-band, satellite-tracking mobile-vehicular antenna system for NASA's ACTS Mobile Terminal (AMT) project. ACTS is NASA's Advanced Communications Technology Satellite, which will be launched into its geostationary orbit in September 1993. The AMT task will make the first experimental use of the satellite soon after the satellite is operational, to demonstrate mobile communications via the satellite from a van on the road. The AMT antenna system consists of a mechanically steered small reflector antenna that uses a shared aperture for both frequency bands and fits under a radome of 23 cm diameter and 10 cm height, and an antenna controller that tracks the satellite as the vehicle moves about. The RF and mechanical characteristics of the antenna and the antenna tracking control system are discussed. Laboratory measurements of the antenna performance are presented     

Modeling three-dimensional scatterers using a coupled finiteelement-integral equation formulation

Finite-element modeling has proven useful for accurately simulating scattered or radiated fields from complex three-dimensional objects whose geometry varies on the scale of a fraction of a wavelength. To practically compute a solution to exterior problems, the domain must be truncated at some finite surface where the Sommerfeld radiation condition is enforced, either approximately or exactly. This paper outlines a method that couples three-dimensional finite-element solutions interior to a bounding surface with an efficient integral equation solution that exactly enforces the Sommerfeld radiation condition. The general formulation and the main features of the discretized problem are first briefly outlined. Results for far and near fields are presented for geometries where an analytic solution exists and compared with exact solutions to establish the accuracy of the model. Results are also presented for objects that do not allow an analytic solution, and are compared with other calculations and/or measurements     

Near field of scattering by a hollow semi-infinite cylinder and its application to sensor booms

The Wiener-Hopf technique is employed to derive the near-field solution for scattering by a semi-infinite conducting tube due to an axially incident plane wave. Numerical results are included and emphasis is given to the interpretation of the results in terms of the error in the measurement of the magnetic field due to the presence of the sensor boom. It is found that at interior resonance frequencies the measurement error can be as large as 100 percent in the immediate neighborhood of the end of the boom. Guidelines for reducing such errors are suggested.     

Adaptive acquisition and tracking for deep space array feed antennas

The use of radial basis function (RBF) networks and least squares algorithms for acquisition and fine tracking of NASA's 70-m-deep space network antennas is described and evaluated. We demonstrate that such a network, trained using the computationally efficient orthogonal least squares algorithm and working in conjunction with an array feed compensation system, can point a 70-m-deep space antenna with root mean square (rms) errors of 0.1-0.5 millidegrees (mdeg) under a wide range of signal-to-noise ratios and antenna elevations. This pointing accuracy is significantly better than the 0.8 mdeg benchmark for communications at Ka-band frequencies (32 GHz). Continuous adaptation strategies for the RBF network were also implemented to compensate for antenna aging, thermal gradients, and other factors leading to time-varying changes in the antenna structure, resulting in dramatic improvements in system performance. The systems described here are currently in testing phases at NASA's Goldstone Deep Space Network (DSN) and were evaluated using Ka-band telemetry from the Cassini spacecraft.     

Radiation from an open-ended waveguide with beam equalizer--A spectral domain analysis

A septum and an impedance matching post are used as a beam equalizer in an open-ended waveguide feed for reflectors used in satellite communications systems. The performance of this design over a frequency band is evaluated using a spectral domain approach. The computed radiation patterns in theE- andH-planes, as well as the results for the impedance match are presented.