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Compact Range

A New Large Compensated Compact Range for Measurement of Future Satellite Generations
J. Hartman (Astrium GmbH, EADS),H.J. Steiner (Astrium GmbH, EADS), J. Habersack (Astrium GmbH, EADS), November 2002

The possibility of launching satellites with increasing volume and weight leads to a higher economy and costefficiency for the service of future communication satellites, which are equipped with platforms up to 12 m in width for a variety of different antennas. For testing the radiation characteristics of the antennas of such large antenna farms, new test facilities are required to be designed and built up. Besides near-field test facilities, compact ranges exist, which provide additionally short test campaigns according to its real time measurement capability. Usually, for communication satellite testing, the highly accurate CCR 75/60 of Astrium GmbH, Germany, was used until now. For the future large satellites, Astrium newly designed the CCR 120/100, which provides a test zone of more than 8 m in diameter. The paper shows the requirements for testing of the large satellite antennas. Further, the design criteria, the range geometry and first simulation results of the CCR 120/100 are shown.

Compact Range Phase Taper Effects Due to Phase Center Shift in Wide-Band Quad-Ridge Feeds
J.A. Fordham (Microwave Instrumentation Technologies, LLC),T. Park (Microwave Instrumentation Technologies, LLC), November 2002

Wide frequency bandwidth feeds are used in compact ranges when multi-octave bandwidth operation of the range is desired. Dual-ridge or quad-ridge horns have been widely used in RCS applications as well as in antenna measurement applications to achieve wide band operation. This selection is made to take advantage of the lower cost of quad-ridge horns vs. other options. In designing a compact range, one primary concern is the beamwidth of the feed over the operating band. This affects the amplitude taper across the quiet zone of the range. Another primary concern is the movement of the phase center vs. frequency of the feed. This directly affects the phase taper across the quiet zone as a result of de-focusing of the reflector. Here we present measured data of the beamwidth and phase center movement vs. frequency of a wide-band quad-ridge feed designed to operate from 2.0-18.0 GHz. Measured and predicted quiet zone performance data over this bandwidth are presented with the feed installed in a Model 5751 compact antenna test range having a 4-foot quiet zone.

A Novel Filter for Software Range Gating
B.A. Baertlein (ElectroScience Laboratory),R. Schulze (John Hopkins University), W.D. Burnside (ElectroScience Laboratory), W.H. Theunissen (ElectroScience Laboratory), November 2002

A filter-based approach to software range gating is presented. Conventional approaches to range gating are widely used and include hard gates applied in the time domain and running average filters applied in the frequency domain. The potential problems with those methods are well understood and involve (1) sideloberelated distortion of the frequency-domain data caused by hard clipping in time and (2) the dual problems that arise from finite-duration smoothing kernels in the frequency domain. Herein, range gating is formulated as a digital filter design problem. We employ a type-II Chebyshev design, which has a maximally flat pass-band and a specified stop-band attenuation. User parameters include constraints on the smoothness of the passband and the width of the gate transition. Edge effects are minimized by filtering symmetrically extended copies of the measured data. The results are illustrated on data acquired by the JHU-APL compact range.

Development of Highly Accurate Measurement Techniques for State-of-the-Art Antenna Test Facilities
J. Hartman (Astrium GmbH),H.J. Steiner (Astrium GmbH), J. Habersack (Astrium GmbH), R. Kis (Intelsat Global Service Corporation), D. Fasold (Munich University of Applied Sciences), November 2002

Contoured multi-beams achieved by multi-feed reflector antennas, realized in modern communication satellites, like Intelsat VIII and IX generations satellite, require an economic measurement of their antenna characteristic. Further, highly accurate, but also fast and therefore real-time measurements are assumed to be applied for the testing of the antenna performance. For that aim, the Compensated Compact Range CCR 75/60, applied at e.g. Space Systems Loral (SSL) in Palo Alto (USA), at ALCATEL in Cannes (France), at the MISTRAL facility in Toulouse (France) and at Astrium GmbH (Germany) was developed and installed by Astrium GmbH. In order to optimize the measurement accuracy of the CCR, detailed error analyses and investigations for improvement measures were performed. Within this paper, the accuracy analyses and improvement steps will be presented in order to establish accuracy values, which can be realized in state-of-the-art compact range test facilities.

AFRL Advanced Compact Range RCS Uncertainty Analysis for a General Target
B. Welsh (Mission Research Corporation),B. Kent (Air Force Research Laboratory/SNS), B. Muller (Mission Research Corporation), November 2002

A calibration uncertainty analysis was conducted for the Air Force Research Laboratory’s (AFRL) Advanced Compact Range (ACR) in 2000 [1]. This analysis was a key component of the Radar Cross Section (RCS) ISO-25 (ANSI-Z- 540) Range Certification Demonstration Project. The scope of the RCS uncertainty analysis for the demonstration project was limited to calibration targets. Since that time we have initiated a detailed RCS uncertainty analysis for a more typical target measured in the ACR. A “more typical” target is one that is much larger with respect to wavelength than the calibration targets and characterized by a wide dynamic range of RCS scattering levels. We choose a 10’ ogive as the target due to the fact it is a large target, exhibits a wide dynamic range of scattering, and the scattering levels can be predicted using readily available CEM codes. We will present the methodology for the uncertainty analysis and detailed analyses of selected component uncertainties. The aspects of the uncertainty analysis that are unique to the “typical target” (i.e., a non calibration target) will be emphasized.

Low Frequency Spherical Near Field Measurement Facility at CNES
P. Dumon (CNES),D. Belot (CNES), L Duschene (SATIMO), P. Garreau (SATIMO), November 2002

In a conventional manner, a majority of compact ranges are currently used between 2 GHz and 200 GHz. Mechanical stiffness limits compact ranges at high frequency and diffraction effects are dominant at low frequency. However, CNES has installed a single reflector with dedicated serrations to perform accurate measurements between 800 MHz and 2 GHz. These serrations are 2 meters long and minimize the ripple in both amplitude and phase within the quiet zone. In order to further improve its measurement capabilities at lower frequencies, CNES has installed, in co-operation with SATIMO, a spherical near field measurement system directly inside of its compact range building. The goal is to measure antennas within the frequency range 80 MHz – 400 MHz with a relatively good accuracy. The spherical near field measurement facility has been tested and validated with four antennas that had been previously measured in the compact range of CNES and other external ranges. This paper focuses in this smart approach, which allows to extend the lower frequency domain of compact ranges. This paper describes in details the measurement facility, the test and the validation of the system.

A Compact Range for RCS & Antenna Measurements: Test Results
N. Balabukha (Russian Academy of Science),Tse-Tong Chia (DSO National Laboratories), A. Zubov (Russian Academy of Science), V. Solosin (Russian Academy of Science), November 2001

Test results of the compact range facility in the National University of Singapore are presented in this paper. The tests were performed for antenna and RCS measurements from L-band to Ka-band. Errors of experimental measurements are compared to errors in measurements calculated by results of field measuring in the quiet zone.

NCTR Research Using POSTECH Compact Range
K-T Kim (POSTECH),D-K Seo (POSTECH), H-T. Kim (POSTECH), J-H Bai (POSTECH), November 2001

This paper presents the results of NCTR research performed at the POSTECH compact range. The radar cross section data of five scaled aircraft models, such as F4, F14, F16, F117 and Mig29, have been measured over a frequency region of X-band and an angular sector of 29.6o. Afterwards, one-dimensional radar signatures at several aspects of each target are obtained by modern spectral estimation techniques, including MUSIC, Fast Root-MUSIC, TLS-Prony, matrix pencil, TLS-ESPRIT. The proposed features are based on the central moments of a given radar signature distribution, and they can provide scale and translation invariance, which are essential for the improvement of NCTR performance. After the appropriate post-processing, the proposed features are classified by the Bayes classifier. Results show that our proposed technique has a significant potential for use in NCTR or ATR areas.

Uncertainty Analysis on the RCS Measurements from Calibration Objects
P.S.P. Wei (The Boeing Company),A.W. Reed (The Boeing Company), C.N. Ericksen (The Boeing Company), November 2001

In order to better estimate the uncertainties in measured RCS for the Boeing 9-77 Compact Range, we study the responses from three high-quality objects, i.e., two ultraspheres of 14” and 8” in dia., plus the 4.5" squat-cylinder, each supported by strings. When calibrated against each other in pairs, the differences between measured RCS and predicted values are taken as the uncertainties for either object. Two standard-deviations from the target, reference, and background, as computed from repetitive sweeps, are taken as the respective uncertainties for the signals. Using the root-sum-squares (RSS) method, the error bars are found to be between + 0.1 to 0.2 dB for most of the frequency F, from 2 to 17.5 GHz. We also analyze the responses from a thin steel wire (dia. 0.020"), supported by fine fishing strings (dia. 0.012"), at broadside to the radar. When the ‘wire and string’ assembly is oriented vertically, the HH echo from the 3-ft metal wire alone happens to be comparable to the HH from the 30-ft dielectric strings. Varying with F4, the combined RCS in HH for the assembly spans a wide range of 38 dB from 2 to 18 GHz. The error bounds are found to bracket the measured traces even when the signals are barely above the noise floor.

Estimating the Contribution to RCS Uncertainty From Non-Planar Illumination in a Compact Range
B. Welsh (Mission Research Corporation),B. Kent (Air Force Research Laboratory), November 2001

Compact RCS measurement ranges all suffer from some level of non-ideal field illumination. Stray fields from interactions with the chamber wall and diffraction effects are major contributors to the non-uniformity of the incident field at the target. This non-uniformity gives rise to unavoidable errors in RCS measurements. We present a detailed analysis of how non-uniform illumination manifests itself into RCS measurement errors. The analysis approach is based on the plane wave spectral decomposition of the illumination. We compute the energy scattered by the planar components of the illumination and determine how much of this energy is coupled backi nto the radar antenna. We model the target as a diffuse scatterer by using a collection of point scatterers distributed within a specified volume. We present uncertainty results based on a simulation as well as field probe data collected from AFRL’s Advanced Compact Range (ACR).

Calibration and Verification Measurements in Compensated Compact Ranges Up to 500 GHz
J. Hartmann (Astrium GmbH, EADS),H.J. Steiner (Astrium GmbH, EADS), J. Habersack (Astrium GmbH, EADS), J. Lemanczyk (ESA/ESTEC), P. De Maagt (ESA/ESTEC), November 2001

Compensated Compact Ranges (CCR) represent a high standard of state-of-the-art test facilities with a fast and real time measurement capability up to the submm wave range. Future scientific and earth observation instruments of ESA/ESTEC such as MASTER, PLANCK and HERSCHEL are working within this frequency ranges and require a high measurement accuracy for large antenna apertures. Within the ADMIRALS study for ESA/ESTEC, transmit and receive modules up to 500 GHz and an appropriate large offset reflector antenna with precise surface accuracy in form of a Representative Test Object (RTO) were applied. Related tests in the CCR 75/60 of Astrium were performed in order to qualify the test facility and verify the antenna measurements with theoretical pattern calculations. The present paper shows measurement results with the highly accurate Plane Wave Scanner (PWS) of Astrium GmbH and the RTO. Through the measurements performed, the accuracy of the plane wave field as well as pattern accuracy in the quiet zone of the CCR 75/60 have been qualified up to 500 GHz.

Modeling of the Antenna-to-Range Coupling for a Compact Range
F. Jensen (TICRA),K. Pontoppidan (TICRA), November 2001

Two ways of modelling a compact range design are presented, and the coupling to a given antenna under test (AUT) is determined and compared to the AUT far field. The compact range models are both based on physical optics (PO). The first model applies a simple presentation of the serrations of the range reflector while the second model is based on a new feature of GRASP8, which allows a detailed description of the triangles of the range serrations. The AUT measurement is modelled by an accurate coupling analysis between the current elements on the compact range reflector and the antenna under test. This coupling pattern is compared to the real far-field pattern and the differences are discussed. By including known range imperfections in the AUT-torange coupling a better agreement to the measured patterns may be obtained. All computations are carried out by GRASP8.

Mitigation of Multipath and Ground Interactions in RCS Measurements Using a Single Target Translation
I.J. LaHaie (AARDC),M.A. Blischke (AARDC), November 2001

Translating pylon terminations are often used in narrowband RCS background measurements as means of separating the returns of the termination from those of the pylon itself. Typically, this is done by measuring the pylon while the fixture continuously translates in the range direction through a distance of at least half a wavelength. This paper describes a translated target processing (TTP) algorithmw hich is an extension of this technique to RCS measurements of rotating targets. The technique is applicable to both narrowband and wideband measurements. The algorithm is applied to the problemof mitigating multipath and ground interaction contamination in indoor and outdoor RCS measurements, respectively. Its performance was evaluated as a function of signal-to-noise ratio, target-tocontamination ratio, and translation distance and accuracy using point target simulations. We conclude with a demonstration of the TTP algorithm using actual measurements from the Boeing 9-77 compact range.

Quasi-Optical Waveguide Modeling Method for Scattering Matrix Measurements in the Near Millimeter and Submillimeter Wave Regions
V.K. Kiseliov (National Academy of Sciences of Ukraine),P.K.. Nesterov (National Academy of Sciences of Ukraine), T.M. Kushta (National Academy of Sciences of Ukraine), November 2001

Earlier (AMTA'97, AMTA'98), we have proposed a new low-cost laboratory method named the quasi-optical waveguide modeling (QWM) method to study power and amplitude-phase scattering characteristics of objects, in particular the RCS of targets or their scale models, in the near millimeter (NMM) and submillimeter (SMM) wave regions. A specific feature of this technique in that an investigated object (or its scale model) is mounted inside a quasi-optical waveguide structure in the form of a hollow dielectric waveguide (HDW), in which the scattering characteristics of the waveguide dominant HE11 mode are determined. These characteristics are related to the wanted scattering characteristics of the test object in free space by definite relationships. At the same time the HDW serves several functions: it forms a quasiplane incident wave within the scattering area where test object is placed, performs the low-loss and low-distortion transmission of the scattered wave carrying information of the object being tested to the receiver, effectively filters the unwanted modes arising at the scattering on the test object, and insulates the measurement area from the ambient conditions containing parasitic sources. In this paper we consider the possibility of using the QWM method to study polarization backward scattering characteristics of physical objects, in particular the complex elements of the scattering matrix with relative phase (SMR). A quasi-optical polarimetric micro-compact range (PMCR) based on the circular HDW and quasi-optical devices has been developed and built. The measurement results of the SMR and backward scattering patterns of a reference object as a square metallic cylinder obtained in the PMCR for the different linear polarization basic sets at the 4-mm wave band are presented. The comparison between the experimental results for the reference object and the theoretical data calculated by the geometrical theory of diffraction have shown a good agreement, and demonstrated the possibilities of the QWM method, and its good perspectives for backward scattering polarization characteristics modeling in the NMM and SMM wave regions.

Positioning System Upgrade of an Existing Measurement System
W. Forster (Mission Research Corporation), November 2001

An accurate and reliable target positioning system is mandatory for a good antenna and/or radar cross section (RCS) measurement facility. Most measurements involve characterizing the radiation or scattering of the unit under test as a function of angle and frequency. Accuracy and repeatability become increasingly important in RCS measurements where background subtraction is utilized. Any error in target position will reduce the subtraction effectiveness. Wear and tear of existing equipment coupled with improvements in motion control technology may compel some measurement facilities to upgrade their positioning system. Doing so, while keeping the rest of the measurement system intact, poses integration challenges that cannot be over emphasized. Problems will inevitably be encountered. Their source could be the new positioning system, the old measurement system, or the communication between the two. Subtleties of how the motion control system works can be overlooked during the requirements definition phase of the project. Further idiosyncrasies can be missed during acceptance testing of the system. The Air Force Research Lab compact range has recently upgraded their target positioning system and will share the lessons learned as a result.

Compact Range for RCS & Antenna Measurements: System Description, A
T-T Chia,N. Balabukha, T-S. Yeo, W-J Koh, Y-B Gan, November 2000

The design of a compact range facility in the National University of Singapore is presented. The range is designed for antenna and RCS measurements from L­ band to Ka-band and for test objects up to about 2 metres in size. The reflector in the range is parabolic in shape with a focal length of 3.5 metres. The instrumentation is standard measurement equipment with some purpose-built controllers for the positioners and the scanner.

Performance of a Well Designed Rolled Edge Compact Range System
I.J. Gupta,R.N. Silz, W.D. Burnside, November 2000

Quiet zone field probe data of a recently built compact range system is presented. The com­ pact range uses an optimally designed blended rolled edge reflector to operate from 800 MHz to 18 GHz. The absorber on the walls, floor and ceiling of the chamber is also designed and placed for optimal performance. It is shown that the range is free of any significant stray signals over the whole frequency band.

RCS Measurement in an Anechoic Chamber in the U/VHF Band: Comparison with Experimental 1:10 Scale Simulation
G. Maze-Merceur,P. Bonnemasson, S. Morvan, November 2000

CAMELIA is a large RCS measurement facility (45m.12m. 13m in dimensions) whose compact range is optimized in the SHF band (1-18 GHz). Exploiting it at lower frequencies requires the modification of the absorbers and the use of huge broad band horns as RF sources (since the compact range is now not well adapted). To help understanding the radioelectric behavior of the large scale facility, we have developed a 1:10 small scale model as well as 1:10 scale horns, that are operated in the SHF band. It enables the experimental simulation of RCS measurements in the V/UHF band. Thus, all dimensions and frequencies are homothetic, only electromagnetic properties of materials are not. RCS measurements of several canonical targets have been performed in both facilities and compared. Due to non directive transmitting/receiving antenna, coupling between the targets and the wans has been exhibited. A simple ray tracing model, taking into account the measured reflection coefficient of the walls and the bistactic RCS of the target, shows good agreement with the measurements.

Near-Field V/UHF Antenna-Array Based RCS Measreument Technique, A
S. Morvan,P. Naud, S. Vermersch, Y. Chevalier, November 2000

Radar Cross Section measurements require the target to be in the far field of the illuminating and receiving antennas. Such requirements are met in a compact range in the SHF band, but problems arise when trying to measure at lower frequencies. Typically, below 500 MHz, compact ranges are no more efficient, and one should only rely upon direct illumination. In this case, the wavefront is spherical and the field in the quiet zone is not homogeneous. Furthermore, unwanted reflections from the walls are strong due to the poor efficiency of absorbing materials at these frequencies, so the measurement that can be made have no longer something to see with RCS, especially with large targets. We first propose a specific array antenna to minimize errors caused by wall reflections in the V-UHF band for small and medium size targets. Then an original method based upon the same array technology is proposed that allows to precisely measure the RCS of large targets. The basic idea is to generate an electromagnetic field such that the response of the target illuminated with this field is the actual RCS of the target. This is achieved by combining data collected when selecting successively each element of the array as a transmitter, and successively each other element of the array as a receiver. Simulations with a MoM code and measurements proving the validity of the method are presented.

Portable Far Field Chamber, A
D. Weatherington,G.A. Sanchez, November 2000

Composite Optics Inc (COI) has designed and constructed a Portable Far-Field Antenna Test Chamber to complement their Large Compact Range. The need for this chamber arose after COI won a contract to design, build, and test hundreds of small broadband antenna elements. Because of the portability requirement, COI chose to procure and modify an industrial container, suitable for transportation on a standard flatbed trailer. This paper discusses the design, fabrication, and installation of a chamber, suitable for pattern measurements of small (<2 feet) antennas in the 6-18 GHz frequency range.







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