Marco Terada

Optimization of gain, impedance and bandwidth in Yagi-Uda antennas using genetic algorithm

A new application for genetic algorithms (GA) is introduced. After the use of this kind of algorithm in electromagnetic problems, especially those related with antennas, the present work proposes bandwidth optimization in Yagi-Uda antennas. In design of an antenna, there is more then one parameter that must be fit. Gain is just one of them, but impedance and bandwidth must also be fit. That is the main reason why a GA is often chosen; it can optimize more then one parameter at the same time and, as a stochastic method, it will not be stuck in a local minimum.

A New Procedure for Assessing the Sensitivity of Antennas Using the Unscented Transform

In this communication, we introduce a new procedure to analyze the sensitivity of antennas. The procedure is based on the method of unscented transform (UT) developed by Julier and Uhlman in 1997. Although the UT is used in control engineering, the method has only recently been applied to electromagnetic (EM) problems. This work describes the application of the UT both for single and multiple random variables cases. The UT method is applied to problems using examples involving different types of antennas. In each example, the UT method is combined with different numerical methods to perform the sensitivity analysis of wire or reflector antennas. In the first example, the results were validated with results from the Monte Carlo technique. The second example investigated the convergence of the UT procedure, and the final example compared UT results with measured data. The main conclusion is that UT is a feasible alternative to the popular Monte Carlo technique, with the advantage of being far less computationally expensive.

Assessment of the sensitivity of the South African KAT-7 and MeerKAT/SKA radio telescope reflector antennas

This paper assesses and compares the sensitivities of the antenna gain, cross-polarization and sidelobe levels with respect to feed and/or subreflector displacements due to estimated operational conditions as well as manufacturing tolerances. The probabilistic assessment is evaluated with the Unscented Transform, deemed computationally more efficient than other similar techniques, and employs physical optics computer simulations performed with the WebPRAC and GRASP computer codes. The procedure is applied to the KAT-7 prime focus parabolic reflector antenna, and to a proposed design for the MeerKAT offset Gregorian reflector antenna.

A novel reconfigurable UWB log-periodic antenna

A reconfigurable ultra wideband log-periodic dipole array (LPDA) antenna is herein introduced. Built utilizing low cost and/or recyclable materials it can cover frequencies from 74 MHz to 2 Ghz, through the discrete adjustment of its elements. The antennas gain in a given frequency band of operation can also be changed by the reconfiguration of its elements. The design, construction and testing processes are discussed and a performance analysis is made based on computer simulations. This antenna can be widely used in developing countries where scarce resources limit both the use of antennas in educational laboratory experiments and their use in industrial applications

Analysis of reflector antennas through the World Wide Web [EM Programmer's Notebook]

This article describes the software WebPRAC (parabolic reflector analysis code for the web). The Internet version was written as a Java applet of PRAC for DOS [1] and PRAC for Windows [2]. PRAC is a user-friendly code designed for analyzing offset parabolic reflector antennas with high precision and accuracy. It has been extensively used over the past decade in teaching (currently, distributed with [3]), research, and industrial development. WebPRAC is intentionally designed for the Internet, running directly from within the Web browser on all usual operating systems (Windows, Linux, Macintosh, Solaris, etc.).

Determination of Measurement Points in Urban Environments for Assessment of Maximum Exposure to EMF Associated with a Base Station

A base station (BS) antenna operates in accordance with the established exposure limits if the values of electromagnetic fields (EMF) measured in points of maximum exposure are below these limits. In the case of BS in open areas, the maximum exposure to EMF probably occurs in the antenna’s boresight direction, from a few tens to a few hundred meters away. This is not a typical scenery for urban environments. However, in the line of sight (LOS) situation, the region of maximum exposure can still be analytically estimated with good results. This paper presents a methodology for the choice of measurement points in urban areas in order to assess compliance with the limits for exposure to EMF.

Estimating the Location of Maximum Exposure to Electromagnetic Fields Associated with a Radiocommunication Station

This paper proposes an approach to estimate the probable location of maximum exposure to electromagnetic fields associated with a radiocommunication station, based only on information of antennas height, half-power angle and tilt. This approach can be implemented when simulation tools are absent, or/and few basic information on radiating system is available. The proposed analytical expression is compared with simulated and real measured data, showing the good accuracy of the proposed technique. The focus of the work are base stations, however the results may be applicable to any radiocommunication station. As far as the authors know, this is the first study to present a mathematical formulation in closed form under the considered constraints.

Computer-aided design of reflector antennas: the Green Bank Radio Telescope

This paper presents an evaluation of the electrical performance of the Green Bank Telescope (GBT) reflector antenna, operating as single- and dual-offset configurations, as well as a general overview of the GBT system. The GBT dual-offset Gregorian configuration is designed for low cross polarization (XPOL) using the dual-offset reflector antenna (DORA) synthesis package code developed by the authors. The procedure implemented in DORA to upgrade an existing main reflector to a low cross-polarized dual-offset Gregorian reflector antenna is also described in this paper. All computed patterns were obtained with the parabolic reflector analysis code (PRAC) program, also developed by the authors, and with the commercial code GRASP7. The GBT radiation patterns and performance values, which include original data not available anywhere else as far as the authors know, indicate that low XPOL performance can be achieved with a dual-offset configuration, provided that a low XPOL feed is used. The GBT configuration is employed as a case example for the aforementioned procedure. However, an effort is made to present the main conclusions as generically as possible.

New method for optimum design of pyramidal horn antennas

This article introduces a procedure for determining the optimum design of pyramidal horn antennas. The efficiencies and phase errors in the optimum design are variables and depend on the design requirements. New equations are proposed for the optimum design, which can be solved numerically or analytically.

Side lobes from radio base station antenna in the evaluation of human exposure to EMF

Maximum human exposure to electromagnetic field associated to a base station is, usually, due to the main lobe of the antenna and is located in the range of some tens to a few hundred meters from its mast. In this paper, we discuss practical situations in which the side lobes of the antenna is responsible for the maximum exposure in distances closer to the base station, even transporting less energy than the main lobe. It will also be presented guidelines to estimate what portions of the pattern of the antenna contributes to the highest field strength. This guidance may be used when few radiating system information is available, like gain, height, tilt and vertical half-power angle, and side lobe level.