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Far Field
Number of Spherical Wave Modes Required for the Prediction of Radiated EMI by a Near-Zone Measurement
Laitinen. T.A.,P. Vainikainen, November 1999
Characterization of radiated EMI by means of near­ zone measurements is examined by computer simulations. Electric field radiated by a test structure is expanded in spherical wave modes. The influence of the number of spherical wave modes on the accuracy to predict the maximum far-field magnitude and the total radiated power is examined. The examinations of this paper support the electric field measurements of small equipment at small measurement distances in the standard radiated EMI frequency range 30 - 1000 MHz. Results are presented as a function kr0, where k is the wave number and r 0 is the radius of the minimum sphere which fully encloses the EUT. Results of this paper give valuable guidelines for choosing an appropriate number of measurement locations for predicting the far field by means of a near-zone measurement.
Number of Spherical Wave Modes Required for the Prediction of Radiated EMI by a Near-Zone Measurement
Laitinen. T.A.,P. Vainikainen, November 1999
Characterization of radiated EMI by means of near­ zone measurements is examined by computer simulations. Electric field radiated by a test structure is expanded in spherical wave modes. The influence of the number of spherical wave modes on the accuracy to predict the maximum far-field magnitude and the total radiated power is examined. The examinations of this paper support the electric field measurements of small equipment at small measurement distances in the standard radiated EMI frequency range 30 - 1000 MHz. Results are presented as a function kr0, where k is the wave number and r 0 is the radius of the minimum sphere which fully encloses the EUT. Results of this paper give valuable guidelines for choosing an appropriate number of measurement locations for predicting the far field by means of a near-zone measurement.
Efficient Dual Mode Antenna Measurement Facility, An
J. Zackrisson,H. Nordgren, November 1999
Saab Ericsson Space and Ericsson Microwave Systems have recently completed the installation of a new efficient test facility. The facility is a fully automated test range designed for high th roughput of measurements. The facility is mainly used for tests of antennas for satellites and for mobile com munication. It is used as a far-field range for small antennas or as a spherical near­ field range for directive antennas. The frequency range covered is 0.8 - 40 GHz. A design driver for the facility was the logistics of measurements, short test time and easy access to the AUT during measurements. To achieve this, high speed positioners and easy access to the AUT via a drawbridge in the anechoic chamber were introduced. The computer controlled RF system allows the use of automatic mode switching to test the AUT in either receive or transmit mode and to change frequencies and mixers without operator intervention.
New Look at the Luneburg Lens Antennas: Design, Optimization and Measurements, A
Y. Rahmat-Samii,H. Mosallaei, Z. Li, November 1999
Design optimization and measurement of the Luneburg lens antennas are the focus of this paper. One of the important design aspects of an optimal Luneburg lens antenna is to construct a high performance lens with as low number of spherical shells as possible. In a uniform Luneburg lens, the gain is decreased and unwanted grating lobes are generated by reducing the number of shells. This deficiency in the radiation performance of the uniform lens may be overcomed by designing a non­ uniform lens antenna. The optimized non-uniform spherical lens antenna is designed utilizing the dyadic Green's function of the multi-layered dielectric sphere integrated with a Genetic Algorithm (GA)/Adaptive Cost Function optimizer. Additionally, a novel 2-shell lens antenna is studied and its performance is compared to the Luneburg lens. Finally, measured results for far field patterns and holographic images are shown for the Luneburg lens antenna using the UCLA's bi-polar near­ field facility.
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.
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.
Projection of Near-Field Data to Far-Field
R.L. McClary, November 2000
Near-field ground-to-ground imaging systems are widely used to discover damage that could degrade the radar signature of low observable vehicles. However, these systems cannot presently assess the impact of this damage on the far-field signature of these vehicles. We describe progress made on a method to accurately project the near-field data from these to the far­ field. Near-field data for the algorithm development is provided by the hybrid finite element/integral equation RCS computer code SWITCH. The near-field data is processed to extract the near-field scattering centers using imaging. The imaging algorithm used differs from the usual far-field imaging formulation in that it incorporates some near-field physics. The processing algorithm, which incorporates a modified version of the CLEAN technique, verifies that the scattering centers that were extracted reproduce the original data when illuminated in the near-field. These near-field scattering centers are then illuminated by a plane wave to produce far-field data. This procedure was tested using VHF band scattering data for a full size treated planform. The near field data was projected to the far-field and then compared to data from a far-field SWITCH computation.
Impact of Alignment Errors on Cylindrical Near-Field Antenna Measurements, The
D.J. Van Rensburg,A. Newell, M. Hagenbeek, November 2000
This paper addresses the sensitivity of the cylindrical near-field technique to some of the critical alignment parameters. Measured data is presented to demonstrate the effect of errors in the radial distance parameter and probe alignment errors. Far-field measurements taken on a planar near-field range are used as reference. The results presented here form the first qualitative data demonstrating the impact of alignment errors on a cylindrical near-field measurement. A preliminary conclusion is that the radial distance accuracy requirement may not be as crucial as was stated in the past. This paper also shows how the NSI data acquisition system allows one to conduct such parametric studies in an automated way.
Anechoic Chamber With Easily Removable 3D Radiation Pattern Measurement System for Wireless Communications Antennas
J. Krogerus,K. Kiesi, V. Santomaa, November 2000
In this paper, a versatile indoor antenna measu rement facility in Nokia Resea rch Center is presented Two measurement systems have been implemented into a rectangular, shielded anechoic chamber having dimensions of 10 m * 7 m * 7 m. The first configuration is an in-house developed 3D radiation pattern measurement system that uses a rotating elevation arm. The primary application of this system is characterization of terminal antennas including the effect of a test person or a human body phantom. The elevation arm can be easily removed and the chamber then used as a conventional 5-m far-field range. This configuration is applied mainly for directive antennas. The facility has been found out to be very useful in research and development of wireless com munications antennas. The 3D spherical scanning system opens up a much wider perspective than before on how the human body interacts with different kinds of terminal antennas and what are the radiation and receiving performance characteristics under realistic usage conditions.
Cellular Band Far Field and Cylindrical Near Field Tapered Anechoic Chamber, A
V. Harding,C. Rizzo, November 2000
A novel, combined far-field and cylindrical near-field tapered anechoic chamber was designed for RACAL Antennas (UK). Advanced ElectroMagnetics Inc. (AEMI) and ORBIT/FR-Europe collaborated in the design and the facility was completed in April 2000. The far-field tapered chamber performance was verified by Shielding Integrity Services. The tapered chamber far­ field facility performance after construction is compared with the original design predictions at several cellular band frequencies. Near-field measurements, in the rectangular section, compare well with outdoor measurements. There is discussion of the installation of the shielded facility and the absorbers intended for engineers interested in the cellular antenna test and measu rement arena.
Cellular Band Far Field and Cylindrical Near Field Tapered Anechoic Chamber, A
V. Harding,C. Rizzo, November 2000
A novel, combined far-field and cylindrical near-field tapered anechoic chamber was designed for RACAL Antennas (UK). Advanced ElectroMagnetics Inc. (AEMI) and ORBIT/FR-Europe collaborated in the design and the facility was completed in April 2000. The far-field tapered chamber performance was verified by Shielding Integrity Services. The tapered chamber far­ field facility performance after construction is compared with the original design predictions at several cellular band frequencies. Near-field measurements, in the rectangular section, compare well with outdoor measurements. There is discussion of the installation of the shielded facility and the absorbers intended for engineers interested in the cellular antenna test and measu rement arena.
Bistatic Radar Cross Section Study of Complex Objects Utilizing the Bistatic Coherent Measurement Systems (BICOMS)
R.L. Eigle,A. Buterbbaugh, W.J. Kent, November 2000
The NRTF and MRC have recently completed the first bistatic RCS test utilizing the Bistatic Coherent Measurement System (BICOMS). BICOMS is the first true far-field, phase coherent, bistatic RCS measurement system in the world and is installed at the NRTF Mainsite facility. The test objects include a 10 foot long ogive and a 1/3 scale C-29 aircraft model. Full pol rimetric, 2-18 GHz monostatic and bistatic RCS measurements were performed on both targets at 17 degree and 90 degree bistatic angles. BICOMS data demonstrates excellent agreement to method-of­ moments RCS predictions (ogive) and indoor RCS chamber measurements (monostatic, ogive). This paper describes the BICOMS system and the test process, highlights some process improvements discovered during testing, assesses the quality of the collected data set, and analyzes the accuracy of the bistatic equivalence theorem.
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.
NFR Cross Polarized Pattern Errors Using a Linear Probe to Measure a Circularly Polarized Antenna
W.G. Scott,R.E. Wilson, November 2000
For greatest efficiency and accuracy in measuring patterns of a circularly polarized antenna on a planar near field range (NFR), a recommended procedure is to use a fast switched, dual circularly polarized probe. With such equipment one obtains complete pattern and polarization data from a single scan of the antenna aperture. For our task of measuring high gain shaped beam apertures, measurement efficiency is further improved by using a moderately high gain (about 12 dBi) probe that has been accurately calibrated for patterns, polarization, and gain over the test frequency band. Such a probe allows scan data point spacing to be typically at least one wavelength, thus keeping scan time minimized with acceptably small aliasing (data spacing) error. The measured near field amplitude and phase data is transformed via computer to produce the angular spectrum that is further processed to remove the effect of the probe patterns, i.e. probe correction. The final output is a set of (principal and cross) circular­ polarized far field patterns. However on one occasion, due to fast breaking changes in requirements, we were unable to obtain a calibrated circular polarized probe in the available time. For this test we used an available calibrated 12 dBi fast-switched dual linear-polarized probe with software capable of processing principal and cross circular-polarized far field patterns. As anticipated, we found from preliminary tests that the predicted low cross-polarized shaped beam pattern was not achieved when using the calibrated fast Ku band probe switch. Further tests showed the problem to be due to small errors in calibration of the probe switch. This paper will discuss test and analysis details of this problem and methods of solution.
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.
Evaluation of the Accuracy of the PTP Phase Retrieval Algorithm by Means of a Numerical/Statistical Approach
C.A.E. Rizzo, November 2000
Obtaining far-field radiation patterns of high frequency antennas (>80Ghz) from near-field measurements has been an important issue in the last twenty years. However with frequencies increasing into the millimetre and sub-millimetre bands, questions have been raised about possible limitations on the assessment of such antennas and in particular the measurement of phase. The PTP phase retrieval algorithm addresses the problem by extracting the phase from the knowledge of two amplitude data sets in the near-field. The accuracy of the algorithm is studied by simulation and measurement by means of a numerical/statistical approach. Pseudo-random phase apertures can be generated using Zernike polynomials, which in turn can be used as initial estimates for the algorithm. This paper shows some simulated and measured results for various separations. It can be seen that different pseudo-random phase functions can affect the accuracy of phase retrieved results in particular when the distance between planes is considerably small in relation to the AUT size.
Radial Field Retrieval and Current Reconstruction for NF-FF Spherical Range
F. Las Hears,B. Galocha, P. Caballero, November 2000
In this paper, an iterative algorithm for the retrieval of the radial component of the electric field is described to be used in matrix source reconstruction methods that deal with spherical measurement. A source-field decoupled integral equations are presented, making it necessary the use of a radial field retrieval algorithm to calculate the equivalent magnetic currents (EMC) in the antenna plane from the angular components of the electric field. The technique is applied in near field to far field (NF-FF) transformations using spherical ranges. With the presented technique, some drawbacks, inherent to the intensive resolution of the integral equations that appears in the methods based on equivalent currents, are overcome. Verification with simulated results as well as measurement results are presented.
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.
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.
TRW's New Compact Antenna Test Range
J. Way,B. Griffin, M. Bellman, R. Smith, November 2000
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.


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