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Analysis

Easy Way to Test Flight Toroidal Antennas Pattern on the Omnidirectional Range of Alcatel Cannes
B. Agnus,A. Rosa, B. Robert, K.V. Klooster, M. Di Fausto, November 2000

When mounted on spacecraft , pattern of some antennas are perturbed by the presence of satellite body. The prediction of antenna performances including satellite structure effect is generally done at early stage of antenna design but is limited in terms of model complexity. The test on full spacecraft & in far field condition is then necessary. This solution is very expensive as it means for test at satellite level to use Compact antenna Test Range in order to satisfy cleanliness aspects. For the Meteosat Second Generation (MSG) program test on the toroidal antennas need to be performed on different model including a flight model. A good compromise was to use the external omnidirectional antenna range and a part of satellite structure representing the major contributor for the antenna pattern as identified via numerical analysis. The external range offer possibilities that cannot be reached in Compact range, e.g. low cost, full sphere pattern, low frequency range.

Architectural Framework for a Universal Microwave Measurement System, An
S.I. Tariq, November 2000

The complexity of modern antennas has resulted in the need to increase the productivity of ranges by orders of magnitude. This has been achieved by a combination of improved measurement techniques, faster instrumentation and by increased automation of the measurement process. This paper concentrates on automated measurement systems, and describes the requirements necessary to make such systems effective in production testing, and in research and development settings. The paper also describes one such implementation - the MI Technologies Model MI-3000 Acquisition and Analysis Workstation - that was designed specifically to cmnply with these requirements The paper discusses several important factors that must be considered in the design of automated measurement systems, including: (1) Enhancing range productivity; (2) Interfacing with instrumentation from a large number of suppliers; (3) Providing a uniform front-end for the measurement setup and operation that must be largely independent of the choice of the hardware configu rations or the type of range (near-field or far-field); (4) Making the test results available in a format that simplifies transition to external commercial and user­ program med applications; (5) Providing powerful scripting capability to facilitate end-user program ming and customization; (6) Using a development paradigm that allows incremental binary upgrades of new features and instruments. The paper also discusses computational hardware issues and software paradigms that help achieve the requirements.

Measured Error Terms for the Three-Antenna Gain-Measurement Technique
G.T. Park,D. Bodner, D. Kremer, D. Musser, J. Snyder, November 2000

This paper will detail the implementation and results of a gain calculation performed on standard gain horns (SGHs) in the LS and XN microwave bands. The three-antenna method was used to ensure the highest accuracy possible, and extensive efforts were made to minimize the error budget. The measurement was performed in a large anechoic chamber, with the receive and transmit antennas placed 4.6 meters high in opposing corners. The resulting fifteen meters of aperture separation (approximately 10D2/l. for LS band and 15D2/l for XN band) eliminated all measurable aperture interactions and greatly reduced multipath interference from chamber reflections. Rigorous analysis of the error terms proved this method to be both accurate and reliable. Typical values of measured error terms will be presented.

Cramer-RAO Bound System-Level Analysis for Multi-Mode Spiral Antennas; Single-Element and Arrayed
B.E. Fischer,K.M. Pasala, R.P. Penno, S.W. Schneider, November 2000

This paper considers the use of Cramer-Rao bound (CRB) to aid in providing accurate and quantitative system-level trades for antenna direction finding (DF). Past work has focussed on the use of spectral estimation techniques (e.g., MLM and MUSIC) to obtain needed DF accuracy. Here, the CRB is used to quickly assess tradeoffs in determining optimal antenna array positioning on a platform system. We develop the necessary CRB mathematical relations and demonstrate the potential advantage of using multimode spiral antennas over a standard linear phase interferometer (LPI). The standard LPI configuration is used as a baseline for comparison.

Implementation of an Advanced User-Interface to Enhance Efficiency in Antenna Measurement and Analysis, The
E. Blasberg,R. Braun, S. Dreizin, November 2000

A software's user-interface design determines how productive someone will be in a accomplishing a given task. This is particularly true in the area of antenna measurement and analysis. The MiDAS software package is used as an example of how software can be specifically designed to focus on enhancing efficiency by implementing an advanced human-machine interlace. Simple yet critical aspects such as minimized menu access, integrated, user friendly error checking and help, and clear, consistent, and integrated features help to improve productivity, reduce errors and save time. In addition, design principles such as having only one interface for all antenna measurement disciplines (e.g., near-field and far-field), reduces the time needed for training which, in turn, lowers costs. This paper explores how the implementation of such a user­ interface can be used as a paradigm for increasing efficiency in the field of antenna measurement and analysis.

Assessment of the NIST DoD RCS Demonstration Project, An
L.A. Muth, November 2000

During the last 6 years scientists at NIST have been focusing on radar cross section (RCS) measurements to improve RCS uncertainty analysis, and to develop new measurement and calibration artifacts and procedures. In addition, NIST has been asked to provide technical support to the DoD RCS self-certification effort. In this talk I review the technical accomplishments of the program, and will make suggestions for future research to improve RCS calibration and measurement technology. I will also present the structure of the certi­ fication process, and discuss NIST's role in the ongoing certification activities.

Progress in Characterizing Measurement Uncertainty for the National RCS Test Facility
E.I. LeBaron,B.E. Fischer, I.J. LaHaie, R.F. Fahlsing, R.J. Jost, November 2000

As a result of Government and Industry RCS Teaming, initial RCS range certification exercises are underway. One critical element of certification exercises is the modeling and characterization of error terms according to the unique properties and requirements of individual RCS ranges, and the development of a method for propagating these errors into overall RCS measurement uncertainty. Previously, we presented the statistical model for the case where errors are grouped into multiplicative and additive classes, as well as a robust methodology for the propagation of errors in both the signal space and RCS (dBsm) domains [1-3]. Initial data at the National RCS Test Facility (NRTF) RAMS site located in the White Sands Missile Range near Holloman AFB, NM, have been collected for range certification exercises. Preliminary analysis has been accomplished on certain dominant error terms for calibration uncertainty characterization only. A general approach [7] has been followed here, with the exception that multiplicative and additive error terms are treated separately. In addition, only variance effects are treated (not bias). This paper is a status of work in progress. The ultimate goal of this work is the full implementation of previously described concepts [1-3]. We plan to demonstrate an improved ability to capture the effects of both error bias and variance (as has been demonstrated mathematically to date) using a more complete set of data collections.

RCS Uncertainty Analysis & Calibration Report for AFRL RCS Calibration Cylinders, An
B.M. Welsh,A.L. Buterbaugh, B.M. Kent, W.G. Forster, November 2000

In order to have definitive measurement traceability according to, ANSI-Z-540, a radar cross section measurement facility must have solid traceability to a known and accepted measurement standard. The Air Force Research Laboratory choose short right circular cylinders as calibration standards for their facilities. We describe a general RCS uncertainty analysis technique, and apply the method to our calibration standards to establish absolute traceability to a known standard. Though applied to cylinders in the current paper, the uncertainty method is general enough for any arbitrary target

Uncertainty Analysis of the Boeing 9-77 VHF RCS Range
I.J. LaHaie,A.M. Gillespie, D.P. Morgan, E.I. LeBaron, November 2000

Boeing is currently pursuing certification of their 9-77 indoor compact range facility as a voluntary industrial participant in the ongoing DoD/NIST RCS certification demonstration program. In support of that process, V­ EI has applied a novel statistical method for analysis to VHF measurements of a canonical target from the Boeing 9-77 range. The dominant error sources in the range were identified and categorized according to their dependence on frequency, aspect angle, and the target under test. Range characterization data were collected on canonical targets and then used to estimate the statistical parameters of each of the errors. Finally, these were incorporated into expressions for the combined RCS measurement uncertainty for a test body whose RCS exhibits many of the characteristics of modern, high-value targets. The results clearly demonstrate the importance of accounting for the target-dependence of the errors and the bias they introduce into the overall uncertainty.

Method to Simulate the Antenna Radiation Patterns Measured in a Compact Range
P.R. Rousseau, November 2000

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.

Time Domain Processing of Range Probe Data for Stray Signal Analysis
I.J. Gupta,T.D. Moore, November 1999

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.

Compact Antenna Test Range Built to Meet the Unique Testing Requirements for Active Phased Array Antennas, A
R. Sauerman,C. Stoffels, November 1999

Microwave Instrumentation Technologies (MI Technologies) in cooperation with Hollandse Signaalapparaten B.V. (Signaal) and the Royal Netherlands Navy has designed and produced a compact antenna test range to specifically address the unique testing requirements imposed in the testing of active phased array antennas. The compact range was built specifically to test Signaal's new Active Phased Array Radar (APAR) prior to introduction into various naval fleets throughout the world. This reversible Compact Antenna Test Range (CATR) allows antenna testing in both transmit and receive modes. The measurement hardware is capable of testing both CW and pulsed waveforms with high dynamic range. In addition to conventional antenna pattern measurements the system is capable of measuring EIRP, Gff and G/NF, as well as providing analysis software to provide aperture reconstruction. A special Antenna Interface Unit (AIU) was designed and built to communicate with the Beam Steering Computer which controls the thousands of T/R modules which make up the APAR antenna system. A special high power absorber fence and other safeguards were installed to handle the transmit energy capable of being delivered from the APAR antenna system.

Calibration and Error Budget in RCS Measurements
L. Oldfield,C. Brewitt-Taylor, T. Elliott, November 1999

Uncertainty analysis for fundamental standards is mature, but the cost overhead has, until recently, prevented much of this work being taken up by the UK RCS measurement community. The requirement to verify the radar signature of new equipment has made it necessary to examine in detail the RCS measurement process and to create a methodology for error budgeting. The paper reviews some basic concepts in estimating uncertainties, and describes work on 'squat' cylinder calibration standards that have been manufactured following designs proposed at previous AMTA conferences. The moment method code CLASP has provided the basic theoretical solutions which have been verified on a compact range through reference to a precise 100mm spherical standard. The concept of multiple standard calibrations is discussed, and recommendations are made for overall error budgeting and the intercomparison of range types.

Interlaboratory Comparison Between the RCS Ranges at FOA Defence Research Establishment and Saab Dynamics, An
J. Lothegard,C. Larsson, C-G Svensson, J. Rahm, J. Rasmusson, J-O. Olsson, K. Brange, M. Andersson, N. Gustafsoon, O. Lunden, November 1999

An interlaboratory comparison is made between radar cross section (RCS) measurements at the test ranges at FOA Defence Research Establishment and SAAB Dynamics, Sweden. The comparison is made in order to increase the measurement and calibration quality at the ranges. An analysis of the deviations in the measured RCS data from the ranges provides a better understanding of the sources of errors. The RCS of two generic targets are measured at the X-band. The targets are simple airplane models, length and width are approximately 1.0 m, with no cavities. A brief comparison between some theoretical results and experimental RCS data are also presented.

Radar Cross Section Calibration Errors and Uncertainties
L.A. Muth, November 1999

To develop standards for radar cross section measurements a complete uncertainty analysis is needed. We derive the radar cross section error equation and examine sources of measurement errors that contribute to the overall uncertainty in calibrations and measurements. We obtain expressions for upper- and lower-bound errors and uncertainties that are generally valid for monostatic measurements on any unknown target using any standard calibration artifact. The general procedure can be extended to bistatic measurements. Some experimental procedures to determine the uncertainty due to background subtraction are presented and discussed.

Technique for Error Analysis of Near-Field Measurement, A
T. Pellerin,G. Seguin, November 1999

The objective of this study is to develop a new techniq ue to compensate the instrumentation errors of an antenna near-field test range. The methodology presented demonstrates that it is feasible to calculate the far-field radiation from near-field measurement with one deconvolution that will include all the errors introduced by the instrmentation. Measrements were performed on a standard gain horn as a reference and the analysis includes a theoretical comparison with a computer model of the standard gain horn, simulated using WIPL. Furthermore, four scenarios of error in the system flatness were analyzed, to verify that the technique is capable of correcting planarity errors.

New DASA Measurement Facility -- RaSigma
D. Bringmann,H. Deisel, November 1999

RCS measurements at in service aircraft often require fast RCS - analysis capabilities. DaimlerChrysler Aerospace therefore extended its RaSigma facilities with a turntable and elevation system especially designed for RCS measurements at aircrafts. The designer and supplier of the turntable and elevation system was the German company HD GmbH. Aircraft with a maximum weight of 75 t can be raised to a height of approximately 13 m. The aircraft is supported by three girders at its landing gears or other hard points. The test range ist 300m long (today) and can increase up to 3000m . RCS measurement are performed in the gated CW mode. The RaSigma outdoor range operates in elevation range mode, with a special antenna design for a homogeneous field distribution over object height and frequency.

Wholebody RCS Estimates from Zone Measurements
G. Fliss,M. Blischke, November 1999

Operationally active hangers are not well suited for making wholebody RCS measurements for aircraft signature diagnostics. While it is much more feasible to make localized regional or zone measurements in a hanger, the utility of such data for determining overall signature growth has significant limitations. The most obvious limitation is not having all the information necessary to re-assemble the wholebody signature. In this paper we present some discussion and experimental results which explore the limiting factors associated with estimating an entire aircraft signature from localized regional (zone) measurements. An example will be shown where zonal measurement data is inserted into a reference image and then reconstructed to form two-dimensional frequency vs aspect angle RCS. It is shown that a precise coherent alignment of the zone image with the reference wholebody image is not necessary and that only a coarse incoherent alignment is needed if only RCS statistics are desired. This is an important finding which leads to conclusion that it is logistically feasible to make zonal measurements and reconstruct a wholebody RCS estimate for impact analysis.

Performance Requirements for a Microwave Cable to be Used in a Near-Field Antenna Range
H.W. Banning, November 1999

A near-field antenna range will often utilize a flexible microwave cable assembly as a means to transport the sampled signal from the moving sample antenna to a receiver as part of the measurement system. The performance of that cable directly impacts the quality of the final far-field pattern. It has been observed that the cable had been exhibiting a flex life much shorter than anticipated. Analysis of a failed cable revealed that the problem was the result of non-uniformities in the extruded jacket, which produced sites of high stress. These sites ultimately caused the cable conductors to work harden and fracture. A cable which utiized a woven expanded Polytetrafluoroethylene (ePTFE) fiber as an outer jacket was substituted, resulting in a threefold improvement in flex life to date, with the cable still in operation at this writing.

Cellular Handset Testing with a Simplified Head Mockup and an Internal Antenna
J.B. Winter,G.R. Kadambi, J.L. Sullivan, M.D. Rhode, T.F. Masek, November 1999

Two types of cellular handset testing are presented. The first studies models of a cellular handset near the human head. A comparative analysis is done between simulation and measurement of an inexpensive head mockup compared to a more expensive head mockup. Peak gain values have good agreement within about 1 dB. The second type of cellular handset testing is for a PCS band PIFA antenna integrated to a cellular handset. This paper describes the design and experimental study of the radiation patterns of a PCS band (1850-1990MHz) cellular handset with an internal PIFA. The PIFA described in this paper has good gain, impedance matching, and reduced sensitivity to human body interaction. This PIFA is a good cellular internal antenna.







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