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Far Field
An Environmental reflection filtering strategy for plane-polar near-field antenna measurement
O.M. Bucci (Universita di Napoli “Federico II”),G. D'Elia (Universitá di Napoli “Federico II”), M.D. Migliore (Universitá di Napoli “Federico II”), November 1996
A new strategy reducing the effect of the environmental noise in the evaluation of the radiated far field by means of a near-field far-field transformation technique is presented. A plane-polar scanning system is considered although the approach holds for general scanning geometries. Numerical and experimental results confirm the effectiveness of proposed the technique.
An Environmental reflection filtering strategy for plane-polar near-field antenna measurement
O.M. Bucci (Universita di Napoli “Federico II”),G. D'Elia (Universitá di Napoli “Federico II”), M.D. Migliore (Universitá di Napoli “Federico II”), November 1996
A new strategy reducing the effect of the environmental noise in the evaluation of the radiated far field by means of a near-field far-field transformation technique is presented. A plane-polar scanning system is considered although the approach holds for general scanning geometries. Numerical and experimental results confirm the effectiveness of proposed the technique.
Phaseless measurements of antenna near fields employing holographic phase retrieval
C.F. Stubenrauch (National Institute of Standards and Technology),Katie MacReynolds (National Institute of Standards and Technology) Allen C. Newell (National Institute of Standards and Technology) Robert H. Cormack (Computational Optics) John E. Will (University of Colorado) John D. Norgard (University of Colorado), November 1996
We describe a technique which employs amplitude-only measurements of an unknown antenna combined with a synthetic reference wave to produce a hologram of a near-field antenna distribution. The hologram, which may be recorded by amplitude-only receiving equipment, is digitally processed using an enhanced theory which allows complete removal of the spurious images normally encountered with optical hologram reconstruction. The recovered near-field data are then processed using standard algorithms to calculate antenna far-fields. We present the theoretical formulation and results of measurements obtained on an 1.2 m reflector antenna.
Simulation of antenna measurement errors caused by clutter sources
T-H. Lee (The Ohio State University ElectroScience Laboratory),R.J. Marhefka (The Ohio State University ElectroScience Laboratory), W.D. Burnside (The Ohio State University ElectroScience Laboratory), November 1996
Simulation of the antenna measurement errors caused by scattering of range clutters is presented in this paper. The Uniform Geometrical Theory of Diffraction (UTD) based NEC-Basic Scattering Code is used to simulate the measurement of antenna in a far-field range where structure scatterers present. It is known that these errors which come from various directions will impact the antenna under test differently dependent on the characteristics of the antenna under test. With the available computer codes, one can simulate and study various ranges in order to better understand the characteristics of the ranges and properly adjust, modify, and improve the facility such that better measurement results can be obtained.
A Position detecting method of reflection sources by distance changing technique
K. Nishizawa (Mitsubishi Electronic Corporation),I. Chiba (Mitsubishi Electronic Corporation), T. Katagi (Mitsubishi Electronic Corporation), Y. Konishi (Mitsubishi Electronic Corporation), November 1996
Residual reflection characteristics should be evaluated for antenna radiation pattern measurements. Authors propose a method for detecting positions of reflection sources by applying the modified far-field antenna radiation pattern measurement scheme described in [1]. In this method, an “accurate” radiation pattern of antenna under test (AUT) and measurement error patterns due to residual reflected waves are separated by changing a range distance and processing Fourier transformation. Also, the positions of reflected sources can be detected from beam directions of patterns due to reflections at each distance. Experiment results confirm that this method is effective for detecting the positions of reflection sources.
Planar near-field antenna measurements using non-ideal measurement locations
R.C. Wittmann (National Institute of Standards and Technology),B.K. Alpert (National Institute of Standards and Technology), M.H. Francis (National Institute of Standards and Technology), November 1996
The standard planar near-field to far-field transformation method requires data points on a plane-rectangular lattice. In this paper we introduce a transformation algorithm in which measurements are neither required to lie on a regular grid nor are strictly confined to a plane. Computational complexivity is O (N log N), where N is the number of data points. (Actual calculation times depend on the numerical precision specified and on the condition number of the problem.) This algorithm allows efficient processing of near-field data with known probe position errors. Also, the algorithm is applicable for other measurement approaches, such as plane-polar scanning, where data are collected on a non-rectangular grid.
Planar, time domain, near-field measurements
A. Dominek (Analytic Designs, Incorporated),H. Shamansky (Analytic Designs, Incorporated), November 1996
In this paper, a near-field time domain radiation measurement is described, similar to the traditional frequency domain near-field radiation measurement. This time domain measurement approach borrows many of the principles developed in the frequency domain and is ideally suited for the measurement of broadband devices. The goal of determining the radiated far-fields of an antenna is accomplished by the transformation of near-field data collected over a planar sampling surface. The near-fields are generated with an antenna excited by a short duration transient pulse. In particular, the near-fields of an aperture antenna are collected using a digital sampling oscilloscope. The bandwidth of the excitation pulse is approximately 10 GHz.
Performance analysis of the image-based near field-to-far field transformation
I. LaHaie (ERIM),E. LeBaron (ERIM), November 1996
At last year’s conference we presented the discrete implementation of an image-based near field to far field transform (IB-NFFFT) for predicting far field radar cross-section (RCS) from spherically-scanned near field measurements, along with some preliminary transform results using numerically-simulated data. This paper quantifies this expected performance in terms of the RCS prediction error (RMS dB difference) using numerically-simulated data for two ten wavelength-long canonical bodies, a thin wire and a conesphere. It will be shown that for the highly-resonant wire target, the NFFFT’s algorithm performance is limited by the multiple interactions resulting from the travelling wave reflections between the end of the wire, except at near broadside aspect angles. Conversely, very good performance is obtained for the conesphere at nearly all aspect angles, except very close to nose and tail-on. We will also shown that the IB-NFFFT algorithm performance is robust with respect to clutter and scan angle coverage.
Antenna near field phase data from infrared thermograms by Fourier iterative plane-to-plane techniques
J.E. Will (University of Colorado),A. Pesta (US Air Force Rome Laboratory), C.F. Stubenrauch (National Institute of Standards and Technology), J. Cleary (US Air Force Rome Laboratory), J. Norgard (University of Colorado), K. MacReynolds (National Institute of Standards and Technology), M. Seifert (US Air Force Rome Laboratory), R.M. Sega (University of Colorado), November 1996
This paper describes the application of the plane-to-plane (PTP) iterative Fourier processing technique to infrared (IR) thermographic images of microwave fields for the purpose of determining the near-field and far-field patterns of radiating antennas. The PTP technique allows recovery of the phase by combining magnitude-only measurements made on two planes, both in the radiating near field of the antenna under test. We describe the PTP technique and show excellent comparisons between the predicted results and results from measured IR thermograms of the field of a 36 element patch array antenna operating at 4 GHz.
Determination of mutual coupling from phased array element patterns
H.M. Aumann (Massachusetts Institute of Technology),F.G. Willwerth (Massachusetts Institute of Technology), November 1996
An examination of mutual coupling effects in a linear phased array is presented. The approach derives mutual coupling coefficients from array element patterns measured in the Fresnel region, at R/D=3. The technique allows edge diffraction effects and mutual coupling effects to be identified and separated. The results are compared with conventional mutual coupling measurements and mutual coupling coefficients determined by numerical integration. The technique is used for far-field pattern reconstruction, and for pattern optimization which corrects mutual coupling effects to the maximum extend possible.
Single-plane collimators for measurements on large antennas
V.J. Vokurka (Eindhoven University of Technology),S.C. van Someren Greve (March Microwave Systems B.V.) S. Cook (Division of Avnet Inc.) I. Henringer (Division of Avnet Inc.), November 1996
For indoor antenna measurements, compact ranges or near-field/far-field techniques are most frequently used. One of the major problems is the handling of physically large antennas. Compact ranges will in general provide test-zone sizes up to approximately 5 meters in diameter. Applying the planar NF/FF technique, even larger test-zone sizes can be realized for certain applications. On the other hand, requirement of real-time capability, for instance in production testing, will exclude NF/FF techniques. It has been shown previously that single-plane collimators have a pseudo real-time capability which makes these devices comparable to compact ranges. Furthermore, the physical test-zone sizes which can be realized when compared to compact ranges are approximately 2-3 times larger for the same size of the anechoic chamber. Finally, it will be shown that the accuracy in sidelobe level determination, gain and cross polarization is considerable higher than with other indoor techniques, even at frequencies below 1 GHz.
Development of a folded compact range and its application in performing coherent change detection and interferometric ISAR measurements
K.W. Sorensen (Sandia National Laboratories),D.H. Zittel (Sandia National Laboratories), J.H. Littlejohn (Geo-Centers, Inc.), November 1996
A folded compact range configuration has been developed at the Sandia National Laboratories’ compact range antenna and radar-cross-section measurement facility as a means of performing indoor, environmentally-controlled, far-field simulations of synthetic aperture radar (SAR) measurements of distributed target samples (i.e. gravel, sand, etc. ). In particular, the folded compact range configuration has been used to perform both highly sensitive coherent change detection (CCD) measurements and interferometric inverse-synthetic-aperture-radar (IFISAR) measurements, which, in addition to the two-dimensional spatial resolution afforded by typical ISAR processing, provides resolution of the relative height of targets with accuracies on the order of a wavelength. This paper describes the development of the folded compact range, as well as the coherent change detection and interferometric measurements that have been made with the system. The measurements have been very successful, and have demonstrated not only the viability of the folded compact range concept in simulating SAR CCD and interferometric SAR (IFSAR) measurements, but also its usefulness as a tool in the research and development of SAR CCD and IFSAR image generation and measurement methodologies.
On the use of lens antennas in the free-space method for measuring dielectric properties of materials
G. Dhondt (University of Gent),Daniel De Zutter (University of Gent) Luc Martens (University of Gent) Hugo Pues (Emerson & Cuming Microwave Products NV), November 1996
In this paper we present an improved theoretical modelling for the free space technique for measuring the complex permittivity of materials at microwave frequencies. The theory was developed for a transmission set-up with two identical pyramidal horn antennas. By performing a spectral decomposition of the aperture fields, the new model takes the effect of the non plane wave character into account when the sample is not placed in the far field of the transmitting antenna. With the use of the new theoretical model it becomes possible to place the sample much closer to the antennas without infringing the theoretical assumptions since no plane wave incidence is needed. In this way the transversal dimensions of the sample can be reduced significantly. The validity of the new theoretical model was verified by measurements on many dielectric (Plexiglas, polystyrene,…) and lossy materials. A comparison was made with the values obtained when the usual plane wave theory is used.
Spherical antenna measurement range enhancement tools
D.A. Leatherwood (Georgia Institute of Technology),E.B. Joy (Georgia Institute of Technology), K.E. Murphy (Georgia Institute of Technology), November 1996
This paper presents several enhancement tools that were developed to improve the Georgia Tech Spherical Far-Field/ Near-Field Antenna Measurement Range. Measurement amplitude and phase drift was quantified by sampling an antenna measurement signal over long time intervals while leaving the AUT rotation positioners fixed. A return-to-point drift correction tool was implemented to correct for the long-term drift component for spherical surface measurements. Temperature sensitive components of the receiver were moved from an area with severe temperature variations to a temperature stable area to reduce the phase variation. A software tool was developed to display a histogram of the variation in repeated spherical scan measurements. Histogram vales show that drift correction improves the repeatability of an antenna pattern measurement. The shapes of the histograms have been helpful in identifying random and deterministic variations.
Errors analysis of near-field measurement
G. Seguin,T. Pellerin, November 1997
The objective of this study is to evaluate the measurement errors of a near-field range at in order to develop some techniques to minimize them. Measurements were performed on a standard gain horn as references. 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 instrumentation
Phase-retrieval using non redundant sampling representations
O.M. Bucci,G. D'Elia, M.D. Migliore, November 1997
A general approach for phase-retrieval is discussed. The representation is based on an advanced non-redundant sampling representation and is able to explicitly take into account geometrical characteristics of the source, like the overall dimension and the general shape, as well as a priori inforn1ation on the near-field and far-field.
Rocket motor plume measurement facility
W.W. Harrington, November 1997
The Plume Measurement Facility is a new outdoor facility providing the capability to characterize tactical rocket motor plumes. Radar cross section of the plume is measured by both a near field and a far field radar. Infrared/ultraviolet/visible (IR/UVNIS) charac­ teristics are measured by numerous instruments recording spacial, temporal, and spectral data. All instrumentation is calibrated and adjusted to realtime standard day meteorological data and all data is recorded on a common synchronized time base.
Implementation and results of a time-domain gating system for a far-field range
A.M. Predoehl,W.L. Stutzman, November 1997
Multipath on far-field ranges causes distortion of pattern measurements. The multipath components can be removed by illuminating the antenna under test with short-duration pulses and applying a time­ domain gate. Equivalently, the measurements can be made in the frequency domain and transformed to the time domain with the Fourier transform. After gating, the time-domain data are transformed back to the frequency domain, yielding improved CW patterns at discrete frequencies. Virginia Tech has recently added time-domain gating capability to its far-field antenna range. The data acquisition and processing software is implemented using the LabVIEW language, which makes the data acquisition and time-domain processing very easy to control. Practical guidelines for selecting a gate are given. Results are presented for an open-ended waveguide and conical dipole. With wideband antennas, gated patterns show significantly improved symmetry and null depth.
Antenna pattern measurement technique using wideband channel profiles to resolve multipath signal components
W.G. Newhall,T.S. Rappaport, November 1997
Wideband channel measurements have been used extensively to determine path loss and time dispersion characteristics of radio channels (e.g., [1], [2], [7]). The principles used to temporally resolve individual received signal components for wideband propagation measu rements can be applied to antenna pattern measu rements to achieve more accurate results. Multipath, a propagation phenomenon which occurs when reflecting or scattering objects exist in an environ ment, causes inaccuracies in measured patterns when narrowband signals (e.g. continuous­ wave) are used to perform far-field antenna measu rements. Using the wideband technique described in this paper, the effects of multipath can be completely eliminated from pattern measurements. The method described here is especially useful when antenna range dimensions are limited in space or when multipath signal components caused by distant reflectors are irreducible.
Quadrille, an error reduction procedure for planar near field measurements, The
L.J. Kaplan,R.E. Wilson, W.G. Scott, November 1997
Coherent processing using measurements on two probe scan planes with different antenna under test (AUT)-to-probe separations reduces the effects of coupling between the AUT and the probe or, alternatively, reduces the effects of room scatter. The results of these doublet scans can be coherently combined to mitigate one or the other (but not both) of these error terms. For either case, the extraneous signals cancel when the far field patterns from the two planes are coherently combined. The new "quadrille" scan technique coherently combines four separate scan planes which will cancel in one set of pattern measurements both the AUT-probe coupling error and the room scatter error. If either the coupling or the room scatter is much larger than the other, the error reduction attained by the quadrille may not merit the additional measurement time; however if the two terms are comparable the quadrille may be needed to attain precise measurements.


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