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The accuracy of near field measurements have in the past largely been judged by inspection however the authors have developed an objective measure of the accuracy and repeatability of such measurements. This paper illustrates the measurement process and the techniques associated with statistical image classification used to confirm its accuracy and repeatability. The technique will be illustrated via the correlation of data sets acquired over a variety of different frequencies and scan plane areas. The examination of these measurements will demonstrate the applicability and sensitivity of the technique when the accurate assessment of highly correlated patterns is required.
The angular coverage of planar near-field measurements is limited by the size of the scan plane, and the "region of validity" is defined by the angle between the edge of the AUT and the edge of the scan plane. In some applications, results are required over a larger angular region than is possible with the available scanner. The angular coverage can be increased by rotating the antenna and repeating the measurement. The results of the two measurements are then combined. Successful combination depends on using both the coordinate system and vector components that are appropriate for the antenna rotation. In general for a single antenna orientation, any coordinate system can be used with any vector components, but when combining or comparing patterns for two antenna rotations, the axis of rotation must be the polar axis and the vector components must correspond to that coordinate system. Measurements results will be used to demonstrate the proper choice of coordinates and components and to illustrate potential problems that may arise.
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.
In order to reduce the cost of building compact range reflectors, a combination of a circular rim reflector and R-card fence can be used. Circular rim reflectors are commercially available at reasonable prices. The R-card sheets are also inexpensive. Since the R-card works as a fence to block/reduce the reflector edge diffraction from degrading the plane wave in the test zone, the manufacturing cost is very low. However, the design is much more difficult since the convex nature of the circular reflector rim diffracts more stray signal into the test zone. Thus, the R-card fence should be carefully designed all around the reflector rim. The optimum continuous resistance distribution is replaced by a discretized one to result in lower cost. The R-card design, that reduces the variations in the test zone for a reflector with a circular rim, will be presented in this paper. Calculated and measured results will be shown for the proposed design.
This paper is focused on a recent installation of a probe array for direct far-field. measurement. Such an array has been installed in a well-established compact antenna test range at CNES called BCMA in Toulouse, France. It describes the interests of using such multi-sensor approach for characterizing directive antennas within far-field conditions without any mechanical movements. The paper shows how this facility has been dimensioned for operating over frequencies ranging from 7 GHz up to 15 GHz. Performances and general descriptions of both the probe array and its associated instrumentation will be given. A specific calibration procedure that has been studied and implemented is discussed and finally preliminary results are shown.
Modern Satellite Antennas and Payloads are characterized by a lot of physical parameters like e.g. Radiation Pattern, Gain, EIRP, Flux Density, Gff and PIM, whereas the available time frame for measurements is getting shorter and shorter. The DSS Compensated Compact Range (CCR) allows a time efficient measurement of all payload parameters with high accuracy under controlled environmental conditions. The CCR consists of two doubly curved reflectors, which prevent inherent cross-polarization and create a very high constant amplitude and phase distribution in the quiet zone with a very good scanning performance. Most of the payload parameters can be measured directly or have to be calculated from a set of measurement values. For the G/T measurement of active antennas a new method for the noise power measurement was established. This paper describes the principle test set-ups with the corresponding measurement techniques to improve the measurement accuracy. Error budgets will be presented for pattern and gain measurement.
A compact range based measurement system for automotive radars is presented. The design driver for the system was production testing. Key characteristics of the system are: compact size, short test times, no need for an anechoic chamber, ease of operation, mobility and ruggedness. The measurement system is based on electronic equipment from Dornier GmbH, the company who developed the automotive radar for the new Mercedes S-Class. It uses a small rolled edge millimeter wave compact range from ORBIT/FR Europe GmbH. Some general characteristics of automotive radars are presented, followed by a more detailed description of the key subsystems of the measurement system: Simulator, Compact Range and Processing Control Unit. Finally some measurement results are presented and discussed.
A network model derived from a moment method solution can be used to form a physically meaningful basis set for an adaptive decomposition of measured scattering data. In recent years, EI has presented techniques for using the network model decompositions for several applications [1,2] including data interpolation, and multipath removal. However, for some applications such as target editing (analogous to image editing) and defect localization, the minimum norm solution, typically used with the network model, does not adequately localize scattering sources to be effective. The reweighted minimum norm (RMN) method [3] is a nonparametric approach by which the localization of the minimum norm solution can be improved by iteratively constraining the solution space in which the minimum norm is computed. In this paper, we will describe how the RMN method can be used in conjunction with the network model decomposition and demonstrate the improved localization properties.
Theory and experiments for a ground wave UWB radar system for human and vehicle detection will be shown. We will consider the case where the radar uses a low gain VP antenna located 20 to 40 cm above the ground and the radar target is a moving vehicle or moving humans out to 200 meters. The nominal frequency for these tests was from 1.0 to 3.8 GHz in a step frequency scan. We will show SIN predictions using the free space radar range equation, then add ground wave attenuation effects. We will then compare these predictions with experimental measurement data for various vehicles and humans. An application using a noise radar as a UWB spread spectrum radar system in this application is our final goal.
RATSCAT has been heavily involved, as part of the DoD Range Certification Demonstration Program, in examining and documenting the underlying principles of all aspects of the outdoor measurement process. Our goal is to replace historical or "anecdotal" measurement approaches with processes founded on validated and documented procedures. This paper reports on the results of two areas of study. These are the effects on measurements caused by wind and calculation of target rotation rates. When RCS targets are measured outdoors on pylons or columns, some uncertainty will be introduced due to the effect of wind on the target and target support structure. This paper will present the results of an investigation into the errors introduced by wind motion on targets mounted on pylons or columns. When rotation rates are determined for target collection, the usual procedure is to employ a rule of thumb like "collecting three points per lobe" or "meeting the Nyquist criterion." This paper examines these common methods to determining rotation rates, and their impact on the measurement of the peak values of RCS magnitude and phase. Finally, the significance of these two measurement errors will be examined in light of their impact on outdoor range operations as well as on decisions based upon the collected RCS data.
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.
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.
The U.S. Navy has considerable experience in the radar cross section (RCS) measurement of dynamic targets. An understanding of the possible error sources and their relative magnitudes is critical to obtaining accurate and repeatable results. In addition to the usual potential sources of error in RCS measurements of stationary items, considerations with dynamic targets include target range and angle tracking, calibration, and various environmental effects. The primary considerations are identified and discussed, and an error budget is developed for a particular test scenario.
In order to assess the suitability of long thin metal rods as calibration devices for both co-polarized and cross-polarized (abbreviated as co-pol and x-pol) RCS measurements, we study RCS data from rods at broadside and compare them with 2D theoretical predictions. We find that the 45° tilt angle is optimum for calibration purposes. Near grazing incidence to a horizontal rod, the first traveling wave lobe in the HH pattern is a very prominent feature. Its angular location and amplitude have been measured as a function of frequency and compared with theory. A formerly unexplained error due to a contaminated calibration is identified.
The accurate measurement of Radar Cross Section (RCS) requires precise calibration "artifacts" as well as carefully executed measurement procedures. The Air Force Research Laboratory (AFRL) reviewed several existing common RCS calibration artifact standards and practices, and identified a number of improvements. Employing a modified "dual calibration" check procedure pioneered by AFRL, this paper demonstrates improved RCS calibration fidelity for a wide variety of static RCS calibration measurement applications. Our calibration results are verified through an industrial inter-laboratory (range) measurement program employing selected calibration artifact standards.
The Georgia Tech Research Institute (GTRI) under contract to the U.S. Air Force 46 Test Group, National Radar Cross Section Test Facility (NRTF) at Holloman AFB, NM, has designed and developed an Automated Field Probe System (AFPS). The AFPS operates as a one-way probe for evaluation of the electromagnetic field at the test zone and provides a mobile capability to rapidly, smoothly, and accurately probe the field at the various test-areas. The AFPS provides the ability to probe over an area as large as 40-ft x 40-ft all under computer control from the radar(s) while sweeping over 1-18 GHz and 34-36 GHz for both H and V polarization. The RF, phase reference, and control signals from the radar are transmitted to the AFPS over a microwave fiber optic link. This paper will describe the design and performance of the AFPS. Quick-look data products will be included in the presentation.
The purpose of this project was to determine the effects of fast neutron bombardment on the radar cross section of metal and dielectric spheres. The energetic neutrons interact with lattice atoms and, in the energy transfer that results, initiate a displacement cascade that effectiveiy damages the crystalline structure of the target material. The induced damage may change the RCS of the target via changes in the conductivity or relative permittivity. Theoretical lattice damage estimates are provided for fast neutron fluences of 1015 n/cm2 and 1016n/cm2. Limitations and potential improvement of damage estimates and measurements are also discussed.
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.
There is a growing interest in generating radar images as data collection is in progress. Such a tool is particularly useful for radar cross section verification purposes where the turnaround time is very important. With the availability of faster processing hardware, real-time radar image formation is now feasible. This paper describes the architecture, operation, and performance of a real time imaging (RTI) system that generates SAR or ISAR images while the data collection is in progress. Real-time performance of the system is benchmarked in terms of image-size and quality (imaging technique), image update rate, and image latency. Several examples of RTI are provided using a Lintek elan radar system.
The interferometric measurements for the structure change detection of a dam due to water level change and to seasonal temperature variation is presented. The instrument used is the Linear SAR (LISA) of the European Microwave Signature Laboratory, which allows two synthetic apertures, one linear of 5 meters length and another circular of about 2 meters. The microwave instrumentation, based on a vector network analyzer and on a pair of wide-band antenna, allows a dual polarized measurement in a frequency band, ranging from 500 MHz to 6 GHz. In this particular context, fully polarimetric measurements have been performed in the frequency band from 5.2 to 6 GHz. From the selected measurements parameters a spatial resolution on the structure of about 30 by 30-cm is achieved. Measurements have been repeated at 7 different dates in the period from June to September. From the set of obtained images a large number of differential interferograms was been formed corresponding to different deformation conditions of the barrage. Results showing the deformation pattern, clearly visible on the whole imaged portion of the structure, are presented. The comparison between measured displacements by D-InSAR and those from the barrage monitoring system in the selected points where traditional tools are installed are in good agreement.