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Far Field
General analytic correction of probe-position errors in spherical near-field measurments
L.A. Muth (National Institute of Standards and Technology), November 1991
A recently developed analytic technique that can correct for probe position errors in planar near-field measurements to arbitrary accuracy [1] is shown to be also applicable to spherical near-field data after appropriate modifications. The method has been used to successfully remove errors in the near-field, hence leading to more accurate far-field patterns, even if the maximum error in the probe’s position is as large as 0.2?. Only the error-contaminated near-field measurements and an accurate probe position error function are needed to be able to implement the correction technique. It is assumed that the probe position error function is a characteristic of the near-field range, and that it has been obtained using state-of-the-art laser positioning and precision optical systems. The method also requires the ability to obtain derivatives of the error contaminated near-field defined on an error-free regular grid with respect to the coordinates. In planar geometry the derivatives are obtained using FFTs [1], and, in spherical geometry, one needs to compute derivatives of Hankel functions for radical errors, and derivatives of the spherical electric and magnetic vector basis functions for errors in the ? and Ø coordinates. The error-correction technique has been shown to work well for errors in and of the spherical coordinates r, ? or Ø. Efficient computer codes have been developed to demonstrate the technique using computer simulations.
Measurement system performance considerations for planar near field scanning applications
J.H. Pape (Scientific-Atlanta, Inc.),O.M. Caldwell (Scientific-Atlanta, Inc.), November 1991
This paper describes measurement system performance parameters that were considered during the design phase of a planar near-field measurement range for Spar Aerospace Limited. All aspects of the planar near-field measurement system are addressed. These include; instrument selection, scanner interface hardware, system controller/computer hardware, software for data collection, near-field to far-field transformation, data analysis, networking and system configuration. The Scientific-Atlanta Model 2095 Microwave Measurement System with its near-field options is used as the basis for meeting the Spar requirement. The various data collection parameters of the Model 2095 are described with special emphasis on how the factors relate to near-field requirements such as fixed grid sampling. Examples of typical test scenarios are presented as an aid in exploring detailed data collection system timing.
A New bi-polar near-field measurement facility: design analysis and development
Y. Rahmat-Samii (University of California Los Angeles),L.I. Williams (University of California Los Angeles), November 1991
A novel bi-polar planar near-field measurement range is described. This range is mechanically simple and has a reduced implementation cost compared to other planar techniques. The particular physical implementation and comparison with the plane-polar range is presented. Development aspects of the customized bi-polar range at UCLA are summarized. An optimal near-field interpolation is used to enable the near-field to far-field (NF-FF) processing via fast Fourier transform (FFT). Computer simulated near-field and far-field results are given.
Antenna far-field from near-field modulus: a phase retrieval strategy
Y.D. Cheung (The University of Sheffield),A.P. Anderson (The University of Sheffield), G. Junkin (The University of Sheffield), November 1991
Far-field pattern prediction of a mm wave reflector antenna from a scan of the near-field modulus is reported. The phase retrieval algorithm utilises minimisation and the generalized error reduction algorithm to retrieve both aperture amplitude and phase from a single planar intensity scan. The far-field pattern is calculated from the retrieved complex aperture. Experimental results from measurement of a 1.12m diameter reflector at 32 GHz are presented to illustrate the practicality of the algorithm for millimeter and submillimeter applications.
Hybrid near-field/far-field antenna measurement techniques
K.W. Lam (March Microwave Systems B.V.),V.J. Vokurka (University of Technology), November 1991
In this paper, an antenna measurement technique based on modified cylindrical NF/FF transformation will be presented. In conventional cylindrical near-field scanning techniques, the near fields are probed on a cylindrical surface surrounding the test antenna. This required extensive data acquisition and processing time which can be reduced substantially if the antenna under test is illuminated by a cylindrical wave. In this hybrid approach, cylindrical wave illumination is generated using a single parabolic reflector in combination with a (point) source. The far-field pattern is then computed by a powerful one-dimensional NF/FF algorithm. It is concluded that this alternative approach combines the attributes of the compact-range technique and the classical NF/FF transformation.
Payload testing in a compact range
R. Torres (ESA-ESTEC),J. Reddy (ESA-ESTEC), P. Bengtsson (ESA-ESTEC), November 1991
The Concept of Compact Test Range has been recently much used for antenna testing facilities, its main characteristic of having far-field conditions in a small and closed place, for a very large frequency band, makes it very attractive. Antenna manufacturers are building them up when the millimetric waves and the spacecraft flight model antennas become part of their activities. The change of the point of view of the antenna characteristics – now, parameters like Gain and Radiation Patterns are replaced by EIRP, Flux Density or Coverage- modifies the classical test philosophy. It makes different the Test Procedures which, in addition, have to take into account the cleanliness and the quality control required for handling flight models, as well. The Compact Payload Test Range (CPTR) in ESTEC shows up a PWZ of 7 x 5 x 5 metres for a frequency range from 1.5 to 40 GHz.; it has been created for testing whole Spacecraft Payloads in space required cleanliness area. The particular properties of the CPTR as such as shielded room, feed scanning, multiaxis test positioner, etc. are used to improve its test possibilities.
Spherical probing demonstrated on a far-field range
R.E. Wilson (Georgia Institute of Technology),D.N. Black (Georgia Institute of Technology), E.B. Joy (Georgia Institute of Technology), G. Edar (Georgia Institute of Technology), M.G. Guler (Georgia Institute of Technology), November 1991
The spherical probing technique for the angular location of secondary scatterers in antenna measurement ranges is demonstrated for an anechoic chamber far-field range. Techniques currently used for source location use measurements of the range field on a line or plane. A linear motion unit and possible a polarization rotator are necessary to measure the range field in this manner. The spherical range probing technique uses measurements of the range field over a spherical surface enclosing the test zone allowing existing range positioners to be used for the range field measurement. The spherical probing technique is demonstrated on an anechoic chamber far-field range with a known secondary reflection source. The plane wave spectrum of the measured range field is computed and used for source angular location. Source locations in the range correspond to the angular locations of amplitude peaks in the spectrum. The effects of the range field probe on this spherical probing is investigated by performing probe compensation.
Arc range test facility
P.R. Franchi (Rome Laboratory),H. Tobin (Rome Laboratory), November 1991
Problems exist with the measurement of large aperture antennas due to the far field requirement. This paper discussed a new method to measure a phased array at about 1/10 the normal far field. The basic idea involves focusing the test array at probe antenna a distance R away from the aperture. In the described measurement technique the probe antenna is placed on an arm that rotates 100º on the focal arc given by Rcos(?). This arc minimizes defocusing due to phase aberrations. To minimize the amplitude errors, the pattern of the probe antenna is carefully matched in order to compensate for the 1/R variation induced amplitude error. The application of this technique will enable arrays to be measured in anechoic chambers, allowing convenient classified testing, while avoiding the effects of weather, and will reduce the risks inherent in the high power testing on transmit. The results of a computer simulation is presented that characterizes the validity and limitations of the technique.
Application of beam space techniques to phased array calibration and fault compensation
H.M. Aumann (Massachusetts Institute of Technology),F.G. Willwerth (Massachusetts Institute of Technology), November 1991
Beamspace techniques are usually employed to synthesize phased array antenna patterns of arbitrary shape. In this paper a beamspace method is used to calibrate the pattern of a 32-element linear array with a conventional array taper. By measuring the antenna pattern in specific directions the beamspace technique permits the actually applied excitation function to be determined with little mathematical effort. Iterative corrections can then be made to the excitation function to maintain low sidelobe performance, or to compensate for element failures. Since local corrections to the array pattern result in global changes to the excitation function, explicit knowledge of where an element failure has occurred is not required. The beamspace analysis was carried out using antenna patterns obtained by electronically scanning the array past a far-field source. Such pattern measurements offer the possibility of maintaining phased array performance in an operational environment.
Plane wave analysis and evaluation of an indoor far field conductive chamber
W.S. Arceneaux (Martin Marietta Company),C. Christodoulou (University of Central Florida), November 1991
Martin Marietta designed and brought on-line an indoor far-field chamber used for radar cross section (RCS) evaluation. The range has conductive walls on all sides except for the pyramidal absorber covered back wall. The chamber was designed such that wall/floor/ceiling interactions occur with a distance (time) delay allowing for their isolation from the test region. Software gating techniques are used to remove these unwanted signals. This paper presents an analysis of the conductive chamber using Geometrical Optics (GO). The objective was to analyze and evaluate the plane wave quality in the chamber test region. The evaluation of the plane wave was performed using the angle transform technique. The measured results were compared to analytical results and measured antenna patterns.
Plane wave analysis and evaluation of an indoor far field conductive chamber
W.S. Arceneaux (Martin Marietta Company),C. Christodoulou (University of Central Florida), November 1991
Martin Marietta designed and brought on-line an indoor far-field chamber used for radar cross section (RCS) evaluation. The range has conductive walls on all sides except for the pyramidal absorber covered back wall. The chamber was designed such that wall/floor/ceiling interactions occur with a distance (time) delay allowing for their isolation from the test region. Software gating techniques are used to remove these unwanted signals. This paper presents an analysis of the conductive chamber using Geometrical Optics (GO). The objective was to analyze and evaluate the plane wave quality in the chamber test region. The evaluation of the plane wave was performed using the angle transform technique. The measured results were compared to analytical results and measured antenna patterns.
Antenna testing by phaseless near zone data: experimental results in the cylindrical case
R. Pierri (2nd University of Naples),G. D'Elia (University of Naples) T. Isernia (University of Naples) G. Leone (University of Salerno) P. Langsford (GEC Marconi Research Center), November 1992
A new near-field far-field transformation procedure, based on only amplitude measurement, is tested from both simulated and measured data. The measurements have been collected at Marconi Research Center and refers to a parabolic reflector working at 9 Ghz. This first experimental validation of the procedure fully support (sic) the feasibility of phaseless near field measurement in the antenna testing.
Planar and Spherical Near field Range of C.A.S.A.
J.L. Besada (University of Madrid),J. Molina (University of Madrid), A. Valero (University of Madrid), L. de la Fuente (University of Madrid), C.E. Montesano (CASA), A. Montesano (CASA), November 1992
The new antenna measurement facility in C.A.S.A. Space Division is described. The system, designed and installed by Grupo de Radiación of the Polytechnic University of Madrid , provides antenna measurement set-up for Far Field and both Planar and Spherical Near Field.
Reconstruction of far-field RCS from the RCS measured in near field
S. Shammas (Israel Aircraft Industries),H. Wineberg (Israel Aircraft Industries), S. Shochat (Israel Aircraft Industries), S. Hendler (Israel Aircraft Industries), November 1992
A method has been developed by which the fair-field RCS of a target can be evaluated from its RCS measured in the near field. The method can compensate for the nonuniformity of the antenna pattern which can be a function of the angle, the frequency, and the target distance. A correction transform is evaluated which depends on the antenna pattern, the frequency, the target distance and the target size. The correction transform is independent of the target geometry. The RCS of a target is measured in the near field, in a band of frequencies around the frequency at which the far field RCS of the target is desired. The method can practically handle directional scattering elements, shading of the scattering elements by each other, and interactions among the scattering elements. The reconstructed RCS evaluated by this method shows excellent agreement with the actual far-field RCS.
Reconstruction of far-field RCS from the RCS measured in near field
S. Shammas (Israel Aircraft Industries),H. Wineberg (Israel Aircraft Industries), S. Shochat (Israel Aircraft Industries), S. Hendler (Israel Aircraft Industries), November 1992
A method has been developed by which the fair-field RCS of a target can be evaluated from its RCS measured in the near field. The method can compensate for the nonuniformity of the antenna pattern which can be a function of the angle, the frequency, and the target distance. A correction transform is evaluated which depends on the antenna pattern, the frequency, the target distance and the target size. The correction transform is independent of the target geometry. The RCS of a target is measured in the near field, in a band of frequencies around the frequency at which the far field RCS of the target is desired. The method can practically handle directional scattering elements, shading of the scattering elements by each other, and interactions among the scattering elements. The reconstructed RCS evaluated by this method shows excellent agreement with the actual far-field RCS.
Semi compact range and its evolution as a fast near-field technique for millimeter-wave applications, The
K.S. Farhat (ERA Technology Ltd., Leatherhead, UK),A.J.T. Whitaker (University of Sheffield, Sheffield, UK), J.C. Bennett (University of Sheffield, Sheffield, UK), N. Williams (ERA Technology Ltd., Leatherhead, UK), November 1992
Increasing use is being made of millimeter-wave systems and there is a need for improved antenna measurement facilities operating at these higher frequencies. Although the practical implementation of compact range and near-field/far-field techniques becomes increasingly difficult, by using a hybrid approach, the attributes of these existing schemes can be exploited and their limitations overcome. The technique uses a linear near-field probe to carry out an instantaneous integration of the field in the date acquisition requirement, together with a quasi-real-time prediction capability. This contribution reviews a number of implementation schemes for the semi-compact antenna test range (SCATR) approach which have been investigated over the past decade and presents the latest results. An implementation of the SCATR with amplitude-only data is presented as an economical and viable method for millimeter-wave frequencies.
Evaluating compact range chamber performance in CSIST
D-C. Chang (Chung Shan Institute of Science and Technology),T.Z. Chang (Chung Shan Institute of Science and Technology), I.J. Fu (Chung Shan Institute of Science and Technology), R.C. Liu (Chung Shan Institute of Science and Technology), November 1992
A 4 foot by 4 foot near field planar scanner is used to evaluate the performance of a SA5751 compact range in CSIST. Using the far field patterns integrated from the scanned aperture fields, the coming directions of the clutters in the chamber can be determined. Often the clutter level is less than the side lobe level of the far field pattern, the scanned field is multiplied by a certain weighting function before integration to pop out the clutter signal. However the weighting method would broaden the main beam and hence clutters coming close along the reflected wave of the reflector are still can not be seen (sic). In this article, a method called main beam suppression, subtracting a constant filed (sic) on the scanned aperture, is introduced to solve this kind of problem and the result shows it serves well for finding those clutters hidden by the main beam and the side lobes nearer to it.
Anechoic chamber diagnostic imaging
G. Hindman (Nearfield Systems),D. Slater (Nearfield Systems), November 1992
Traditional techniques for evaluating the performance of anechoic chambers, compact ranges, and far-field ranges involve scanning a field probe through the quiet zone area. Plotting the amplitude and phase ripple yields a measure of the range performance which can be used in uncertainty estimates for future antenna tests. This technique, however, provides very little insight into the causes of the quiet-zone ripple. NSI's portable near-field scanners and diagnostic software can perform quiet-zone measurements which will provide angular image maps of the chamber reflections. This data can be used by engineers to actually improve the chamber performance by identifying and suppressing the sources of high reflections which cause quiet-zone ripple. This paper will describe the technique and show typical results which can be expected.
Generating linear probe data from spherical probe data
R.E. Wilson (Georgia Institute of Technology),D.N. Black (Georgia Institute of Technology), E.B. Joy (Georgia Institute of Technology), M.G. Guler (Georgia Institute of Technology), November 1992
Linear probing is used to evaluate test zone quality and detect extraneous field sources on fixed-line-of-sight far-field and compact antenna ranges. Field probing along a line allows the measurement and meaningful display of range field amplitude and phase taper. Since positioners used with far-field and compact ranges are spherical, linear probing requires extra equipment, namely a linear scanner. This paper will present a new technique for generating linear probing data from measurements made with the existing spherical positioners. The steps necessary for implementing this new technique will be presented and demonstrated using measured data.
Far-field spherical microwave holography
M.G. Guler (Georgia Institute of Technology ),D.N. Black (Georgia Institute of Technology ), E.B. Joy (Georgia Institute of Technology ), R.E. Wilson (Georgia Institute of Technology ), November 1992
This paper reports on Far-Field Spherical Microwave Holography (FFSMH), currently being researched at Georgia Tech. Microwave Holography is a technique for evaluating complex electric fields near the field sources. Planewave Microwave Holography involves the use of the planewave spectrum and is the most common technique in use. Spherical Microwave Holography involves the use of a spherical expansion of Maxwell's equations and is the topic of this paper. Spherical Near-Field Microwave Holography (SNFMH) has been successfully used to locate and identify defects in radome walls, and to determine antenna aperture distributions. FFSMH differs from SNFMH only in the location of the measurement surface. FFSMH uses a far-field measurement surface and SNFMH used a near-field measurement surface. Progress in the definition of resolution limits for Spherical Microwave Holography is reported. FFSMH is demonstrated and results are compared to SNFMH and Planewave Microwave Holography


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