Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
The Compact Range is becoming the method of choice for indoor testing of many types and sizes of antennas. Implementation of a compact range requires a suitable parent building structure in which to house the chamber. The chamber is located within the parent building and the compact range is then installed within the chamber. In some cases an existing building may not be available for the range and it may be difficult to acquire a new building due to local or proprietary requirements. Once a building has been located, many problems still exist with coordination installation of the chamber and compact range within this building. Overcoming these problems can be both time consuming and inefficient in terms of cost. This paper describes a Compact Antenna Range conceived and designed to be totally self contained and truck transportable. The compact range consists of a complete anechoic chamber facility with self contained electrical, lighting, HVAC and fire protection systems. The compact range provides a 3 foot test zone over the 5.8 to 94 GHz frequency range. Once completed and tested at the factory, the facility is transported and set in place at the user site. Details are presented which describe the structural requirements of the chamber, the RF performance of the completed facility, and the transport and installation process. The integrated test positioner and an automatic feed changing mechanism are also described.
Traditional Compact Range Antenna (CRA) applications are related to Antenna Pattern and RCS measurements. For these purposes, as a rule, CRA are installed within or outside of an anechoic chamber as stationary equipment. However, for some modern applications, such as Electronic Warfare development, radar tracking system testing, indoor RF environment simulation and others, where dynamic and pointing properties of an AUT are to be tested, the mobile and multi-beam CRA is of great importance, since it provides the designer with powerful simulation and testing capabilities. Such a CRA has been designed, built and tested at ORBIT ADVANCED TECHNOLOGIES, LTD. The design trade-offs, CRA analysis, test set-up and results are discussed in the presented paper.
This paper considers an electromagnetic field simulation of an anechoic chamber with experimental verification. The simulation is a Geometric Optics (Ray Tracing) mathematical model of the direct path between two antennas and interfering scattering. There are two separate models due to the frequency dependent nature of the pyramidal radar absorbing material (RAM). The model for the frequency range of 30 to 500 MHz was used to characterize the specular scattering. The specular scattering was modeled as a lossy, tapered, TEM transmission line in an inhomogeneous anisotropic tensor material. The frequency range from 500 MHz to 18 GHz was characterized by dominant tip diffraction of RAM patches and the model made use of a Uniform Theory of Diffraction code for a dielectric corner. The measurements and simulations were based on an azimuthal cylindrical scan. Diagnostic measurements were also performed by a cylindrical scan of a directional horn antenna to locate scattering sources in the chamber. A cylindrical wave, modal expansion of the diagnostic data which included a one dimensional Fast Fourier Transform with Hankel function expansions.
The U.S.Army Redstone Technical Test Center (RTTC), Test and Evaluation Command, has developed a comprehensive antenna metrology and Radar Cross Section (RCS) evaluation facility. This facility features the compact antenna test range technique for millimeter wave measurements and the near-field scanning technique for microwave measurements. This paper described RTTC's use of these measurement techniques, instrumentation with PC Windows based automation software, anechoic chambers, and types of tests performed. Planned future thrust areas are also discussed.
Anechoic chambers have difficulty in meeting the new basic standards for radiated emission and susceptibility test facilities that have come into operations by the new EMC directive of the European Economic Community. In this contribution a method first presented at the 1992 A.M.T.A. meeting is extended to compute the performance of anechoic chambers at the most critical lower MHz frequency range. Computational results are shown of a real semi-anechoic chamber with a sloped ceiling and a symmetrical reference chamber. The results are compared with measurements values obtained by scanning the chamber with a small field probe. Following this, several methods for optimizing the chamber performance are proposed and evaluated in their effectiveness. The goal of this work is to achieve an accreditation of existing as well as chambers still to be built as standardized EMC test facilities in the specified frequency range.
The simultaneous illumination of the Quiet Zone by number of beams is helpful and cost-effective for broadband antenna and RCS measurements. For an application such as, for instance, Electronic Warfare development, the use of scanning beam or multiple beams gives more extensive opportunities for designers. When the antenna-under-test is small in size, the lightweight and small single reflector Compact Range is very well suited for the above applications. Such a Compact Range being moved within the test facility (anechoic chamber or outdoor range) provides additional flexibility for the tests. This paper describes the development of a small Compact Range with a rolled edge reflector and a two-foot diameter Quiet Zone. Analysis of the Compact Range is performed for different feed positions, providing the beam scan in elevation and azimuth with respect to on-axis beam.
Traditional techniques for evaluating the performance of anechoic chambers, compact ranges, and far-field ranges involve scanning a field probe through the quiet zone area. Plotting the amplitude and phase ripple yields a measure of the range performance which can be used in uncertainty estimates for future antenna tests. This technique, however, provides very little insight into the causes of the quiet-zone ripple. NSI's portable near-field scanners and diagnostic software can perform quiet-zone measurements which will provide angular image maps of the chamber reflections. This data can be used by engineers to actually improve the chamber performance by identifying and suppressing the sources of high reflections which cause quiet-zone ripple. This paper will describe the technique and show typical results which can be expected.
The measurements of an antenna at FM frequencies integrated in the bodywork of a terrestrial vehicle is a extremely (sic) delicated (sic) problem that will be larger if a ground plane must be simulated. An algorithm based on two measurements (magnitude and phase of the field components E() and E (1) on a scale model made in an anechoic chamber, has been developed to solve this problem. These measurements correspond to the value of the desired conical cut (only a narrow range of angles above the horizon is significant), and the associated cut needed to measure the specular reflection on the simulated ground plane.
The anechoic chamber housing the TUD-ESA Spherical Near Field Far Field Antenna Test Facility at the Technical University of Denmark dates back to 1967 while the present RF and data collection and control systems were designed and installed in several stages between 1978 and 1985. This paper undertakes to describe the definition and realization of a refurbished and upgraded radio anechoic facility for antenna measurements given as a starting point the already existing facility. In a parallel effort, both the RF and data collection and control subsystems are being renewed and upgraded.
As many institutions and companies have constructed anechoic chambers in the past few years, there has been little work done to codify the specification requirements. Often chambers have been constructed from woefully inadequate specifications resulting in chambers that may be too costly, unable to meet the performance criteria, and in some cases, be unsafe. This paper shall present various model specifications and guidelines to properly specify a chamber complex. Compact ranges, tapered chambers, as well as traditional rectangular chambers will all be examined. How to specify absorbing materials and quiet zone sizes, as well as tradeoffs associated with them, will be discussed. Finally, a guide for coping with facility concerns such as civil, structural, RF shielding, HVAC, electrical, and fire protection will be presented. Examples of good specifications and inadequate specifications will be demonstrated and reviewed.
Most of the present available pyramid absorber lined anechoic chambers do not meet the new stringent requirements (plus or minus 4 dB criterion of CISPR) for EMC measurements at lower frequencies, say below 100 MHz, due to poor absorber efficiency. In this paper the actual field configuration in those chambers at these critical frequencies is numerically computed for extracting frequency dependent correcting relations for EMC measurements. To this end a finite difference formulation in frequency domain is used. The absorbers are modeled as planar dielectric layers. Examples of computed field configurations are presented and compared with measurement values. The results show the frequency response of the electrical field configuration with respect to the position of device under test, the test antenna, as well as the effect of chamber asymmetries.
A method for measuring G/T of small gain active antennas has been developed. The measurement can be carried out inside an anechoic chamber with well controlled environment. The method has been validated by measurement of a simulated active antenna, whose G/T has been computed from the parameters measured by classical procedures.
Two measurement systems for Radar Cross Section (RCS) measurements are described. One system employs propagation over a ground plane whereas the other system employs free space propagation in an anechoic chamber for target illumination. A comparison of measured data for different targets over a wide range of frequencies is presented. The measured data is also compared to RCS data computed using the Numerical Electromagnetics Code (NEC) computer program. The results may be useful for evaluating radar systems operating in the HF band of frequencies.
Recently, the theory and computer programs on the Periodic Moment Method (PMM) for scattering from both singly and doubly periodic arrays of lossy dielectric bodies have been developed. The purpose is to design microwave wedge and pyramid absorber for low reflectivity so that one can improve measurements and/or reduce the size of the anechoic chamber. With PMM, the reflection and transmission coefficients of periodically distributed bodies illuminated by a plane wave have been accurately calculated on the Cray Y-MP supercomputer at the Ohio Supercomputer Center. Through these studies, some wedge and pyramid absorber configurations have been designed, fabricated and tested in the OSU/ESL Anechoic Chamber. Very good agreement between calculations and measurements has been obtained. In the 1990 AMTA meeting, several wedge absorber designs and results for the TM case and normal incidence were presented. In this paper, the measured and calculated frequency responses of some experimental wedge designs, as well as an 8” and 18” commercial wedge and pyramid absorber panels will be reported for both TM and TE polarizations. Time domain responses will also be shown for both measurements and calculations.
The accuracy of antenna measurements can be improved by compensating for the effects of extraneous fields present in an antenna range using analytical compensation techniques. Range field compensation is a new technique to provide increased measurement accuracy by compensating for extraneous fields created by refection and scattering of the range antenna field from fixed objects in the range and by leakage of the range antenna RF system from a fixed location in the range. The range antenna field must be the dominant field in the range, and the range field cannot change for different AUTs. Existing compensation techniques are limited in the amount of compensation they can provide. The range field is measured over a spherical surface encompassing the test zone using a low gain probe. The measured range field is used in subsequent antenna measurements to compensate for the effects of extraneous fields. This technique is demonstrated using measurements simulated for an anechoic chamber far-field range.
A procedure for the calculation of the effect of backwall reflections in a compact antenna test range (CATR) is shown. In the calculation, the magnitude of the backwall reflections known from previous work and the angular spectrum of the reflections measured in this work are used. The angular spectrum of the scattered reflections from the back part of an anechoic chamber was found to be very wide (>±45º), and the effect of backwall reflections was found insignificant, especially in a CATR with a long effective focal length.
The RAFAEL general purpose radome measurement range has been modernized and refurbished, maintaining its capability to accommodate all range of radome sizes up to 1.2 meters in diameter. It is based on a 3-axis positioner placed in an open anechoic chamber with a null seeker placed 20 meters away and about 10 meters above the ground. All the positioner’s axes are controlled by an automatic positioner controller. The receiver and source are based on a HP-8510B system. The X-Y null seeker serves for boresight error measurements. It has a 0.7m x 0.7m total motion span, which is about 2º. It is controlled by a dual-motor controller, so that the scanning antenna can be moved in any kind of motion. Instrumentation control and data acquisition and analysis is performed using a HP-330 UNIX controller. Present software handles monopulse antennas with or without a comparator, and can implement the comparator in software. There are two major measurement modes: One for BSE measurements and the other for radiation patterns.
The prototype of the March Microwave Single-Plane Collimating Range (SPCR) has been in operation at Arizona State University’s ElectroMagnetic Anechoic Chamber (EMAC) facility for approximately three years. The unique SPCR produces a cylindrical-wave test region by bouncing spherical wavefronts off a parabolic cylindrical reflector. Consequently, a simplified algorithm can be applied to determine antenna far-field patterns. Both computation and acquisition times can be reduced considerably when compared to classical NF/FF cylindrical scanning techniques. To date, this is the only SPCR in operation. Some of the fundamental quantities which characterize an antenna/RCS measurement range are the size and quality of the “quiet zone”, usually expressed in terms of ripple and taper of the illuminating fields relative to an ideal planar wavefront. Direct one-way probing of the quiet zone fields in the vertical and horizontal planes has been recently completed at ASU. An overview of the range geometry, the field probing methodology, and the data processing will be presented. The results of the quiet zone scan will be presented as amplitude ripple, amplitude taper, and phase ripple versus frequency from 4 GHz to 18 GHz in four bands. The vertical-scan phase deviations are relative to an ideal planar wavefront, while those of the horizontal scan are relative to an ideal cylindrical wavefront.
Portable near-field measurement systems can provide significant flexibility to both large companies seeking to increase their antenna test capabilities, and small companies looking for their first investment in a test range. There are many unique applications for portable near-field antenna measurement systems in addition to their use for standard antenna performance measurements. Some additional applications include flight-line testing, anechoic chamber quiet zone imaging, and EMI testing. Many of NSI’s near-field systems have been portable designs, capable of being set up in a small lab or office and easily relocated. Key features required for use of a portable system are rapid setup, simplicity of use, low cost, and accuracy. This paper will be focused on practical experience with installing, calibrating, and operating portable near-field measurement systems. It will also cover tradeoffs in their design, and usage in a variety of applications.
A panelized 56 by 50 foot compact range reflector with a wrap-around rolled edge treatment was installed in an anechoic chamber. Good quiet zone performance required that the as-built surface precisely follow the theoretical cosine blended contour. Commercially available CAD/CAM software served as the design platform for development of the overall system layout, rolled edge panel designs and the CNC milling machine source code for contour machining the rolled edge panels. Formed aluminum and machined composite panel fabrication techniques are described, and resulting aggregate surface accuracies as good as 1.0mil rms are presented. The use of multiple triangulating theodolites, photogrammetric measurements with peak accuracies of 0.5 mils, and custom bestfitting software used in surface alignment are described.