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This paper describes how ANSI/NCSL standard Z- 540 [1, 2] was applied in a DoD demonstration project to organize radar cross section (RCS) range documentation for the Air Force Research Laboratory (AFRL) Advanced Compact Range (ACR) and the Naval Ai:r Warfare Center - Aircraft Division (NAWC-AD) Atlantic Test Range (ATR) Dynamic RCS measurement facility. Both parts of this paper represent a follow-up report on the DoD demonstration program introduced at AMTA 97 [3]. In June 2000, the DoD Range Commanders Council Signature Measurement and Standards Group (RCC/SMSG) certified that these two facilities met the ANSI/NCSL Z-540 documentation standards established by the DoD demonstration project. Since AFRL plans to require mandatory ANSI/NCSL Z- 540 compliance for DoD contractors performing RCS measurements with AFRL after January 1, 2004, the review process described in this paper will be the likely model for industrial compliance. Part I of this paper contained a brief summary of the ANSI/NCSL Z-540 standard, outlined the certification review process and discussed the outcomes, results, and lessons learned from the DoD demonstration program from the perspective of the AFRL range and volunteer range reviewers. Part II will discuss the review process as it applied to ATR, as well as the outcomes, results, and lessons learned.
Allgon Systems AB has put a new compact antenna test range into operation in July 2000. The investment was triggered by Allgon's planned move to a new building. An indoor facility was preferred for fast and efficient operation. The present primary application is the measurements of base station antennas. The compact range is constructed using a single reflector with serrated edges. A sophisticated feed carrousel enables automatic changing of 3 feed systems. The size of the quiet zone is 3 meters. The initial frequency range is from 800 to 6000 MHz. However, the reflector accuracy allows future extensions to 40 GHz and higher. The cha mber size is 21 x 12 x 10.5 m (L x W x H). Absorber layout comprises 24, 36 and 48 inch absorbers. An overhead crane spans the entire facility. The positioner system is configured as roll over azimuth with a lower elevation over azimuth for pick-u p and small elevation angle measurements. Different sizes of masts and roll positioners are available, depending on the AUT. Instrumentation is based on a HP 8753. Software is based on the FR-959 Plus. Antenna measurement results show the performance of the facility.
GE Aircraft Engines (GEAE) in Cincinnati, Ohio recently built a compact range facility to operate from 800 MHz to 18 GHz. The design process included visits to other :recently completed facilities so that industry best practices could be incorporated into the design of the state-of-the-art facility. The facility includes a 30 x 30-x 65-ft. chamber, corner fed blended rolled edge reflector, Chebyshev Multilevel absorbers, a 12-ft. diameter tu rntable, and rail mounted gantry crane for target mounting, Facility design, chamber, reflector, absorber, target handling and fire protection systems are discussed.
This paper presents the electromagnetic effects of low level non-random error on a compact range reflector surface. Physical optics computational analyses are presented illustrating the effect. Furthermore, actual case study results from the new GE/NT Compact Range Facility are also shown in which a non-random error of 3 mil RMS was discovered. Finally, a process is presented in which the non-random nature of the error was analyzed and removed from the surface. Before and after field probe measu rements illustrate the dramatic effect of such error.
An important source of error in a compact range antenna pattern measurement is the deviation of the quiet-zone field from the perfectly fiat amplitude and phase of a plane wave field. Although some guidelines and rules of thumb exist that relate the quiet-zone field to the error in the measured antenna patterns, the error or perturbation is dependent on the particular type of antenna that is being measured. For example, the non-ideal quiet zone field will produce very different errors for a small horn than for a large phased array. A realistic error budget or uncertainty analysis of the compact-range measurement requires knowledge of the antenna pattern uncertainty as a function of the quiet-zone field and the particular antenna of interest. A simulation method is derived using reciprocity that allows one to quantify the perturbations induced in a given antenna pattern when the quite-zone field distribution is known. This is particularly useful, since one typically has a fair estimate of the antenna pattern and has measured data of the quiet-zone field. The simulation is tested by modelling the antenna as a collection of elemental current sources and simulating the quiet-zone field as generated by elemental current sources. Using this simple simulation model, a closed-form near-field antenna pattern may be calculated for comparison with the more general computer simulation derived from reciprocity.
Many aircraft radome structures are designed to operate simultaneously over multiple RF bands and incident polarizations. Critical parameters must be measured over the electrical apertures of the radome and across each operating band. Automated measurement techniques are required to efficiently collect the large volume of test data required. A modular broadband feed assembly has been developed to allow the simultaneous collection of multi-band, multi-polarization data on a compact range without the need to mechanically change feeds. The feed assembly utilizes a sinuous antenna as the radiating element and is capable of operation from 2-18 GHz with electronically selectable polarization states. Feed design criteria as they relate to compact range antenna and radome measurements are discussed. Of primary importance are reflector illumination pattern, linear polarization cross-polarization level, and circular polarization axial ratio. Polarization switching requirements for a specific test application are defined and the physical implementation of the integrated feed assembly is described. Measured feed and quiet zone performance data is presented for this application. The polarization switching configuration can be readily modified to support other applications.
Nowadays, highly accurate antenna pattern and RCS measurements are performed in compensated compact range test facilities, which fulfil the stringent space requirements for measurements up to 500 GHz and more. As the suppression of diffracted fields from the reflectors mainly determine the quiet zone field performance, the reflector edge treatment is an important design parameter for this type of test facilities. Within the present paper a novel serration design wm be shown. The analyses as well as measurement results exhibit a clear improvement of the quiet zone field performance when compared to previous solutions. The new serration design was implemented and proved with the CCR 20/17 of Astrium GmbH at the Munich University of Applied Sciences.
Compact ranges have found wide use in the pa rametric characterization of high performance radomes such as those found on modern military aircraft. A properly designed compact range facility provides a stable, repeatable test environment suitable for the measurement of small variations in antenna boresight position (beam deflection), antenna pattern distortion, and transmission loss. Radomes have increased in complexity from small structures housing a single antenna to multi-band, multi-system structures large enough to stand inside. Similarly, compact range reflectors have increased in commercial units available today provide quiet zone extents of 12 feet or larger. This paper describes the system design and performance of a compact range test facility designed to test a C-130 Combat Talon II nose radome measuring 7 feet in length and diameter. The facility was constructed at Robins AFB, GA, and is in operation. A description of the facility and its major subsystems is given. Sizing of the chamber and layout of equipment is described. Chamber electromagnetic design considerations are discussed. Electromagnetic design was complicated by the physical size of the structure required to mount the radome, by the fact that multiple antennas and gimbals are present inside the radome during testing, and by the need to use a broad band feed to eliminate mechanical feed changes. Absorber layout and control of spurious reflections is discussed. Electromagnetic performance data is presented.
TRW, working with several subcontractors, is building a Compact Antenna Test Range (CATR) in one of its existing buildings. This range will replace the function of a two mile long far-field range. Lehman Chambers Corp. provided the CATR Anechoic Chamber with Cuming Corp. Microwave Absorber. Mission Research Corp. provided the CATR Rolled Edge Reflector and feeds. M.I. Technologies is configuring TRW supplied positioners with new translators for AUT positioning. The system will operate with both the M.I. Technologies 3000 System software and TRW software. We will be using an existing S/A 1795 receiver for the RF portion of the system with HP sources. Completion of the range is scheduled by the beginning of the 4th quarter 2000. This paper will provide an overview of the system design and constraints. Individual portions of the CATR will be described in detail including decisions made to reduce the overall cost of the system and fit into an existing budget.
This paper summarizes a joint NIST-Industry measurement effort. The purpose of this effort was to use a NIST developed ultrawideband measurement system to assess the performance improvement of ferrite tile anechoic chamber after a partial retrofit. Measurements were performed in the 30-1200 MHz frequency range before and after treatments were applied and excellent results were obtained. The system exhibited good sensitivity and the results highlight the effects of various retrofitting treatments. The effort also demonstrates that the NIST ultra wideband system is an efficient tool for the evaluation for both current and proposed anechoic EMC compliance test chambers.
A reconstruction method that calculates bi-dimensional equivalent magnetic currents from the tangential electric field components over a hemispherical region is presented. The method is applied for diagnosis as well as for near field to far Field (NF-FF) transformation. The method is well suited for antenna radiation pattern measurement using a near-field spherical acquisition system in anechoic chamber.
An efficient algorithm for the RCS evaluation of the Monostatic Radar Cross Section (RCS) from a reduced set of bistatic near-field data is proposed. The algorithm allows to evaluate the monostatic RCS from near field data collected in an angular region centered on the direction of interest, whose amplitude depends on the size of the scatter and the distance of the measurement zone. Numerical examples on two dimensional elliptical cylinders show the effectiveness of the proposed technique.
This paper presents the theoretical derivation of the G/F parameter, a simple method for measuring this parameter in a Compact Anechoic Antenna Range, a study case, and the error associated with the G/F approximation as a function of antenna temperature and system noise figure.
Time domain processing (TDP) is used to analyze the quiet zone fields of antenna/RCS ranges. To carry out the time domain analysis, the quiet zone fields are probed over a band of frequencies. It is shown that TDP is a very effective tool for analyzing probe data. One can not only estimate the time and direction of arrival of various signals present in the quiet zone, but can also estimate their frequency dependence and quiet zone variations.
Error budget projections of measurement accuracy require statistical descriptions of the individual error sources. Thermal noise errors are well known and commonly used. Such statistics, however, have a zero mean Gaussian distribution and sadly are misapplied to the distributions of other error sources. The class of coherent RF errors, for example, has non-zero mean values and variances that differ from Gaussian values. Such statistics are described.
A method for implementing and/or improving background subtraction performance in wideband outdoor RCS range measurements is described. The method estimates and corrects for systematic changes that have occurred between a test and back ground measurement. Results from the application of a phase-only version of the techniques to background measurements from the RATSCAT RAMS facility are presented. Background subtraction performance improvements of as much as 20 dB are demonstrated.
This paper examines candidate configurations for a smart radar absorber or reflector which is capable of self-tuning and perform while scan operation. The discussion is supported by both modelled and measurement data.
In early 1999 a number of broadband absorbers were tested to evaluate their high power performance. In this paper the procedure for the tests is described and some results are presented. Later this year some additional tests were done to see effects of cooling by forced air. A conclusion is drawn that a standard procedure for verification of the high power capabilities of absorbers is needed in industry and that existing high power absorber does not necessarily meet specification as stated.
This paper describes the alignment procedure for using a spherical near-field measurement facility to determine incident fields throughout a spherical volume. This information can be used, for example, to characterize an anechoic chamber or the quiet zone of a compact range. A probe is mounted on a standard roll-over-azimuth positioner and aligned looking out of the sphere so its aperture maps out the surface of a sphere. The probe measures the amplitude and phase of the fields incident on the sphere. This method differs from the standard spherical near-field measurement where the source antenna serves as the probe and is looking into a sphere containing the test antenna.
In this paper we discuss the experimental issues encountered in the measurement of the local electromagnetic fields in the reactive region of a scattering or radiating body using the NRL Near-Field Facility. Our investigations require high-resolution measurements, reaching spatial resolutions of small fractions of wavelength, high polarization sensitivity, and broad bandwidth. We present techniques currently successfully being used in these investigations. The complexity of the reactive zone fields imposes difficult requirements on probe designs. Currently, the NRL probes include coaxial and coplanar configurations. We will discuss their properties and characterization. Design trade-offs to reach spatial resolutions of one-tenth of a wavelength, bandwidths of several giga-hertz and limitations on polarization sensitivity will be addressed. We will correlate these observations with the results of the back-propagation algorithms being developed at the Naval Postgraduate School.