AMTA Paper Archive


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Near Field

Using a Tracking Laser Interferometer to Characterize the Planarity of a Planar Near-Field Scanner
P. Rousseau (The Aerospace Corporation),C. Turano (The Aerospace Corporation), J. Proctor (MI Technologies), W. Wysock (The Aerospace Corporation), November 2002

This paper describes the experience of using a tracking laser interferometer to align and characterize the planarity of a planar near-field scanner. Last year, The Aerospace Corporation moved their planar near-field antenna range into a new larger room with improved environmental controls. After this move, the near-field scanner required careful alignment and characterization. The quality of the scanner is judged by how accurately the probe scans over a planar surface. The initial effort to align the scanner used a large granite block as a planarity reference surface and cumbersome mechanical probe measurements. However, a tracking laser interferometer was used for the final alignment and characterization. The laser interferometer was included as part of an alignment service purchased from MI Technologies. The tracking laser interferometer emits a laser beam to a mirrored target called an SMR (Spherically Mounted Retroreflector). Encoders in the tracker measure the horizontal and vertical angles while the laser interferometer measures the distance. From these measurements, the three-dimensional SMR location is determined. The laser has the ability to very accurately (within about 0.001 inch) measure the location of the scanning near-field probe. This paper includes a description of the mechanical alignment of the scanner, the tracking laser interferometer measurements, and the final planarity characterization.

Improved Procedure for NFR Error at Off-Probe-Calibration Frequencies
R. Wilson (Space Systems/Loral),W. Scott (Space Systems/Loral), November 2002

Calibrated probe complex pattern data is used in planar NFR (near field range) data processing to remove the effects of the probe on the measurement. In a prior paper [1] we proposed a procedure to estimate the measurement error (uncertainty) introduced into a near field antenna radiation pattern measurement due to test frequencies that do not coincide with available calibration frequencies of the range probe. Our prior paper resulted in a “19th term” which was added to the well known NIST NFR 18 Term Error Table used to evaluate the unavoidable uncertainty of far-field radiation patterns derived from a near field scan of a given AUT (antenna under test). A limitation of this procedure, pointed out in our prior paper, is that it was most accurate for a test frequency falling midway between two nearest neighbor probe calibration frequencies. The estimated uncertainty became overly pessimistic as the test frequency of interest moved closer to one of the neighboring calibrated frequencies. The procedure is improved in the present paper by the inclusion of a new term that is a function of the test frequency and the two nearest neighbor probe calibration frequencies. Examples are shown of the use of the new procedure to obtain an improved estimate of this measurement uncertainty and to create the 19th term for use with the standard 18 Term Error Table.

Statistical Analysis of Near Field-to-Far Field RCS Transformation Performance
I.J. LaHaie (Veridian Ann Arbor Research and Development Center),D.J. Infante (Veridian Ann Arbor Research and Development Center), E.I. LeBaron (Veridian Ann Arbor Research and Development Center), P.K. Rennich (Veridian Ann Arbor Research and Development Center), November 2002

In previous AMTA presentations, we developed and evaluated an image-based near field-to-far field transformation (IB NFFFT) algorithm for monostatic RCS measurements. We showed that the algorithm’s far field RCS pattern prediction performance was quite good for a variety of frequencies, near field measurement distances, and target geometries. In this paper, we quantify the statistical RCS prediction performance of the IB NFFFT using simulated data from a generalized point scatterer model and method of moments (MoM) code, both of which allow modeling of targets with single and multiple interactions. It is shown that the predicted RCS statistics remain quite accurate under conditions where the predicted far field patterns have significantly degraded due to multiple interactions and other effects.

Chamber Design 101
G. Sanches (Advanced ElectroMagnetics, Inc.), November 2002

This paper will deal with basic rectangular chamber design and the choices that most affect the performance characteristics of a typical Rectangular Anechoic Chamber. The first and foremost criterion that needs to be addressed is “What is the chamber for”. The answer to this question is the primary driving factor regulating the overall chamber design. Is the chamber to be used to evaluate low gain, low frequency antennas? Is the chamber going to be used for RCS measurements of unique test bodies? Is the chamber going to be used to test high gain high frequency antennas? Is the chamber going to be used for far field measurements? Is the chamber going to be used for near field measurements? On and on. The answers to these very basic questions have a dramatic effect on the overall design of the anechoic chamber. Since there are so many preliminary criteria that have to be decided before we can even attempt a design I will make the following assumptions: 1) The chamber is to be a far field antenna measurement facility 2) The chamber is to operate from 2.0 Ghz to 18.0 Ghz 3) The chamber is to be of a rectangular design 4) The quiet zone is to be a 4’ diameter sphere 5) The range length is to be 20’ 6) The desired Quiet Zone performance is a. –30 dB @ 2.0 Ghz b. –40 dB @ 4.0 Ghz c. –50 dB @ 10.0 Ghz d. –50 dB @ 18.0 Ghz With these parameters we will first look at the effect that source antenna selection has on the chamber deign. The first design example will be with a low gain broadband antenna chosen as the source and the second case will be with a high gain antenna chosen as the source. This paper will detail the different design approaches that this choice has on the overall size and absorber placement in the chamber. These will have a dramatic effect on overall chamber size and cost.

The New Anechoic Test Range at NPL
P.R. Miller (National Physical Laboratory),A. Beardmore (National Physical Laboratory), D.G. Gentle (National Physical Laboratory), Edward Johnson (National Physical Laboratory), P.D. Lovelock (National Physical Laboratory), November 2002

NPL has recently commissioned a new indoor test range. This test range has been designed to offer Extrapolation Gain Measurements, Far-Field Probe Calibrations, and eventually, a Spherical Near-Field Test Capability. This paper describes this new range and the results of the initial validation measurements. It also compares the gains of a standard gain horn calibrated in NPL’s old Extrapolation Range with those from the new one.

Test-Chamber Imaging Using Spherical Near-Field Scanning
R.C. Wittmann,M.H. Francis, November 2001

Although the theory is straightforward, practical implementation of spherical near-field scanning for evaluating test chambers presents some significant challenges. Among these are the requirement for accurate probe positioning and the difficulty in minimizing support-structure blockage. We report on recent NIST efforts to mitigate these difficulties and present our most recent results.

Prediction of BTS Antennas Safety Perimeter from NF to NF Transformation: An Experimental Validation
A. Ziyyat (Mohammed 1st University),D. Picard (Supélec), J.Ch. Bolomey (Supélec), L. Casavola (Bouygues Telecom), November 2001

This paper presents a near-field approach for the characterization of BTS antennas. Thanks to Near-Field Near-Field transformation, the near-field radiated by an antenna and its safety perimeter can be determined rapidly and very accurately. An experimental validation of this approach is provided.

A Historical Overview of Planar Near-Field Antenna Measurements at NIST
R.C. Baird (National Institute of Standards and Technology), November 2001

The National Bureau of Standards pioneered in the development of practical planar near-field measurement techniques for antennas. The basic theory was originally developed to determine a diffraction correction for a microwave measurement of the speed of light. Subsequently, this theory was adapted to antenna measurements, and NBS undertook the development of techniques for characterizing antennas from measurements in the near field. Implementation required development of (1) precision near-field scanners for measuring the phase and amplitude of EM fields over a precisely determined measurement plane, (2) efficient computer algorithms capable of processing large quantities of data, and (3) error analyses for reliably estimating the uncertainties in the computed antenna characteristics.

A Historical Overview of Planar Near-Field Antenna Measurements at NIST
R.C. Baird (National Institute of Standards and Technology), November 2001

The National Bureau of Standards pioneered in the development of practical planar near-field measurement techniques for antennas. The basic theory was originally developed to determine a diffraction correction for a microwave measurement of the speed of light. Subsequently, this theory was adapted to antenna measurements, and NBS undertook the development of techniques for characterizing antennas from measurements in the near field. Implementation required development of (1) precision near-field scanners for measuring the phase and amplitude of EM fields over a precisely determined measurement plane, (2) efficient computer algorithms capable of processing large quantities of data, and (3) error analyses for reliably estimating the uncertainties in the computed antenna characteristics.

Planar Near-Field Scan Plane Truncation Applied to the Measurement of Large Phased Array Antennas
C. Smith (Lockheed Martin), November 2001

An empirical study on Planar Near-Field Scan Plane Truncation applied to the measurement of a large phased array radar antenna saves test time per antenna. Lockheed Martin has been manufacturing, aligning, and verifying the AEGIS SPY-1B/D phased array radar antenna for the past 17 yrs . A custom built planar nearfield scanner system (ANFAST II) was designed and built specifically for this purpose. Existing raw near-field measured data sets were cropped in both the X and Y scan planes, processed to the far field, and compared with the un-truncated data to determine the error sensitivity vs near-field amplitude level truncated. Near-field measurements were then acquired at the truncated scan plane dimensions and compared. It was demonstrated that 100 hrs of test time could be saved by applying this technique without adversely effecting the antenna measurement uncertainty. This paper discusses the application of the truncation technique, results of the experiments, and practical limitations.

Measurement and Correction of the Phase Errors Introduced by Flexing of Cables in Sub mm-Wave Planar Near-Field Testing
J. Saily (Radio Laboratory),A.V. Raisanen (Radio Laboratory), P. Eskelinen (Radio Laboratory), November 2001

Flexing of cables in planar near-field test systems may introduce significant phase errors to the measured vector values of the field. Submm-wave receivers require several flexible cables to be connected to them. The phase errors originated in the bending cables get multiplied and added to the phase of the final detected submm-wave signal. A complete submm-wave antenna measurement system with on-the-fly measurement of the phase errors in a flexing microwave cable is presented. The phase error measurement is based on the use of a pilot signal. Correction of the detected vector values is done as a postprocessing step. Quiet-zone fields and the corresponding phase error planes have been measured at 310 GHz for two different-sized CATRs based on a hologram. The measured maximum phase errors were 7o and 11o for 30 cm and 60 cm holograms, respectively.

Novel Spherical Near-Field Antenna Measurement Techniques Advances State-of-the-Art
A.R. Howland (ATDS-HOWLAND ),C.W. Sirles (ATDS-HOWLAND ), M.H. Sewell (ATDS-HOWLAND), November 2001

Widespread deployment of cellular phones and use of wireless devices such as personal digital assistants, in-vehicle installs of Global Position-ing System (GPS) receivers, and the upcoming deployment of mobile satellite digital audio has sprung a revitalized interest in faster, more af-fordable measurement techniques for antennas. This paper presents information on several new Spherical Near-field antenna measurement ranges developed by ATDS-Howland.

Holographic Projection to an Arbitrary Plane from Spherical Near-Field Measurements
A.C. Newell (Nearfield Systems Inc.),B. Schluper (Nearfield Systems Inc.), R.J. David (The Mitre Corp.), November 2001

Holographic back-projections of planar near-field measurements to a plane have been available for some time. It is also straightforward to produce a hologram from cylindrical measurements to another cylindrical surface and from spherical measurements to another spherical surface1-7. In many cases the AUT is approximately a planar structure and it is desirable to calculate the hologram on a planar surface from cylindrical or spherical near-field or far-field measurements. This paper will describe a recently developed spherical hologram calculation where the farfield pattern can be projected on any plane by specifying the normal to the plane. The resulting hologram shows details of the radiating antenna as well as the energy scattered from the supporting structure. Since the hologram is derived from pattern data over a complete hemisphere, it generally shows more detail than holograms from planar measurements made at the same separation distance.

On the Use of Wavenumber Migration for Linear SAR Image Formation and Near-Field to Far-Field RCS Transformation
B. Fischer (AARDC),I.J. LaHaie (AARDC), J. Fliss (AARDC), November 2001

This paper presents a first-principles algorithm for estimating a target’s far-field radar cross section (RCS) and/or far-field image from extreme near-field linear (1- D) or planar (2-D) SAR measurements, such as those collected for flight-line diagnostics of aircraft signatures. Wavenumber migration (WM) is an approach that was first developed for the problem of geophysical imaging and was later applied to airborne SAR imagery [1], where it is often referred to as the “Range Migration Algorithm (RMA)”[2]. It is based on rigorous inversion of the integral equation used to model SAR/ISAR imagery, and is closely related to processing techniques for near-field antenna measurements. A derivation of WM and examples of approximate farfield RCS and image reconstructions are presented for the one-dimensional (1D) case, along with a discussion of the angular extent over which the far-field estimates are valid as a function of target size, measurement standoff distance, and near-field aperture dimensions.

Limitations of Near-Field Back Projection for Phased Array Tuning Applications
D.J. Van Rensburg (Nearfield Systems Inc.), November 2001

Simulated data is presented for a planar array to demonstrate the limitations of planar near-field back projections. It is well known that the result obtained in this way is of limited resolution and accuracy and these limitations are further illustrated through the data presented here. The impact of probe to AUT separation distance is shown as well as the correspondence between array excitation perturbations and that detected through the back projection technique. Results are shown for a simple iterative array excitation adjustment process. The purpose of this paper is to provide guidelines for the application of the planar near-field back projection technique.

Large Array Diagnosis From Non-Redundant Near-Field Measurements
O.M. Bucci (Università di Napoli “Federico II”),M.D. Migliore (Università di Napoli “Federico II”), G. Panariello (Università di Cassino), P. Sgambata (Università di Napoli “Federico II”), November 2001

This paper presents an accurate method for diagnosis of element failures in large phased arrays. The method is based on the reconstruction of the excitation from measured near-field data by solving the linear system relating the excitation coefficients to the field at measurement points. The dimension of the linear system is reduced by adopting sampling strategies with minimal redundance. The strongly ill-conditioned system is solved using an iterative generalized Landweber algorithm. Numerical simulations on a 2225 elements planar array confirm the effectiveness of the approach.

Broadband Dielectric Probe for Near Field Measurements
C-C Chen (ElectroScience Laboratory),P.A. Diez (ElectroScience Laboratory), W.D. Burnside (ElectroScience Laboratory), November 2001

A novel broadband dielectric rod probe design that has the characteristics of broad bandwidth; symmetric probe pattern; low RCS; low antenna clutter and dual polarization operation is discussed. The RCS level reduces the interaction between the probe and antenna under test (AUT). The lower antenna clutter level improves the sensitivity in detecting responses from wide angles with greater time delays. During the transmission mode, the rod is excited with a broadband microwave launcher from one end. The radiation then occurs at the other terminal of the rod. Measurement results of the far-field patterns, RCS and reflection coefficient for a prototype rod probe (DRP) are presented.

Controlling Scattering From Near-Field Probes Without Using Absorbers
A. Frandsen (TICRA),O. Breinbjefg (Technical University of Denmark), Pivnenko. S. (Technical University of Denmark), November 2001

The level of multiple reflections in near-field antenna measurements is an important issue in a measurement error budget. Traditionally, the interactions between the test antenna and the measuring probe have been reduced by covering the probe mounting structure with absorbing material. In this paper, a novel approach to alleviating the problem is discussed. This implies the use of a skirt to act as a shield against the mounting structure behind the probe, thereby eliminating the need for an absorber, which is a fragile material when exposed to wear and tear. This also has the added advantage that probe calibration data will not depend on a particular absorber that must be considered as an integral part of the probe. With a suitable design of the skirt, the level of multiple reflections can be reduced, whilst at the same time maintaining the pattern of the probe in the boresight direction unchanged. Prototypes of probes for 20 GHz and 30 GHz have been manufactured and tested, and excellent agreement between experimental results and theoretical predictions has been observed.

Near Real-Time Spherical Near-Field Antenna Measurements
D. Burrell (e-tenna Corporation),P.O. Iversen (Satimo), Ph. Garreau (Satimo), S. Rogers (e-tenna Corporation), W. Klimzcak (e-tenna Corporation), November 2001

High growth in the mobile telephone industry is forcing the development of new terminal antennas at an everincreasing pace. The future multi-standard telephones demand antennas that need to be designed and tested for a variety of radiation and bandwidth specifications. New wireless communications devices, such as those using the new Bluetooth and IEEE 802.11 standards, will require testing of a whole range of new products containing antennas, such as computers, household appliances and consumer electronics. The radiation characteristics of the small antennas used in such devices are strongly dependent on the environment into which they are radiating. For example, the presence of the operator or the mounting and positioning equipment of a test set-up can severely change their radiation characteristics. etenna Corporation addresses this problem by employing a Satimo spherical near-field test system. This system allows for rapid, and in some cases, real-time observation of in situ antenna patterns. A brief description of the test facility is presented in this paper along with sample data.

A Simple Analysis of Near-Field Boresight Error Requirements
D.W. Hess (MI Technologies), November 2001

The need to measure the boresight pointing direction of radar antennas to a high degree of accuracy yields a requirement for excellent positioning accuracy on near-field antenna ranges. Evaluation of this requirement can be accomplished by a full and complete sensitivity analysis. Alternatively, to gain an understanding of the effects of errors more simply, one can approach the question of accuracy required in the setup, by use of a physical model and straightforward physical reasoning. The approach starts with the assumptions of a collimated wave with planar phase fronts and the premise that the boresight direction of such a sum beam is along the normal to the phase fronts. A sensitivity analysis of the simple trigonometric boresight relationship between mechanical boresight and phase front normal, shows how accurate the receiver and the positioner must be to achieve a given boresight determination. Such an approach has been known for many years as it regards planar scanning; and, the results are known to be applicable. In this paper this consideration is extended to spherical scanners to arrive at estimates of the mechanical positioner accuracies and electrical receiver accuracies needed to make boresight measurements of radar antennas with spherical near-field ranges.







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