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Polarization
Near-field measurement experience at Scientific-Atlanta
D.W. Hess (Scientific-Atlanta, Inc.), November 1991
The experience with near-field scanning at Scientific-Atlanta began with a system based upon a analog computer for computing the two-dimensional Fourier transform of the main polarization component. When coupled with a phase/amplitude receiver and a modest planar near-field scanner this system could produce far-field patterns from near-field scanning measurements. In the 1970’s it came to be recognized that the same advances, which made the more sophisticated probe-corrected planar near field measurements possible, would enable conventional far-field range hardware to be used on near-field ranges employing spherical coordinates. In 1980 Scientific-Atlanta first introduced a spherical near-field scanning system based upon a minicomputer already used to automate data acquisition and display. In 1990, to meet the need of measuring complex multistate phased-array antennas, Scientific Atlanta began planning a system to support the high volume data requirement and high speed measurement need represented by this challenge. Today Scientific-Atlanta is again pursuing planar near-field scanning as the method of choice for this test problem.
The Calibration of probes for near field measurements
J. Lemanczyk (Technical University of Denmark),F. Jensen (TICRA Consultants), November 1991
In near field antenna measurements, knowledge of the the [sic] probe antenna’s pattern, polarization and gain are of vital interest. To calibrate a probe for near field measurements is a delicate task, especially if the probe is small, i.e. low gain. The near field probe and the parameters general to a probe calibration are presented. The delicate task of obtaining an accurate gain for small aperture antennas as well as the problem of transfering [sic] the calibration from the facility where the probe is calibrated to the facility where it is to be used are focussed [sic] upon For a small aperture, the pattern is that of the radiating aperture. The unwanted scattering may be removed by filtering in the spherical mode domain thus obtaining the true aperture radiation. The gain derived from this may however be of little use in reality since the aperture always needs some form of mounting. Such a mounting may be covered with absorber which may reflect and diffract and thus affect the gain value.
Application of RCS antenna measurements to multiport antennas
E. Heidrich (Institut fur Hochstfrequenztechnik und Elektronik),W. Wiesbeck (Institut fur Hochstfrequenztechnik und Elektronik), November 1991
New results of wideband polarimetric radar-cross-section-(RCS-) antenna measurements are presented. A special antenna network description including polarization information and multiport feeding offers new insight in antenna behavior. The procedure omits the utilization of a standard gain antenna for absolute gain determination and no RF-feedline is necessary to the antenna under test. Antenna radiation, scattering and feed characteristics are all obtained with one measurement setup. Theory as well as measurements on different dual-polarized antenna types demonstrate the efficiency and uniqueness of this technique.
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.
Synthesis method of a compact range feeder for a given field distribution in the quiet zone
J.E.C. Herrero (TeDeCe),C.M. Pascual (TeDeCe), November 1992
The proposed synthesis method allows the calculation of the diffraction figure in the focal plane of the compact range, starting from a field distribution in linear polarization over a plane in the Fresnel zone. Applying this method (in only one dimension) to the ideal near field of a FFOC compact range, a linear array is synthesized which can be extrapolated to a planar array feeder design; providing excellent features in the quite zone.
Field probe for the USAEPG compact range
O.D. Asbell (Georgia Tech Research Institute),J.M. Hudgens (Georgia Tech Research Institute), November 1992
The Georgia Tech Research Institute has designed and built a field probe for the U.S. Army Electronic Proving Ground Compact Range. The field probe is an R-0 scanner covering a 59-foot diameter area. It includes a laser-referenced Z-axis correction servomechanism, a polarization positioner, and a cable handling system for one-way data acquisition.
An Instrumentation radar system for use in dynamic signature measurements
C.T. Nadovich (Flam & Russell, Inc.),D.R. Frey (Flam & Russell, Inc.), J.F. Aubin (Flam & Russell, Inc.), November 1992
The dynamic, polarization/frequency diverse, Instrumentation Radar System (IRS) described herein combines the features of an X-band radar tracker with a wideband, fully polarimetric coherent data collection system. Mounted in a transportable trailer, the system can be towed to virtually any site to acquire radar signature measurements on moving aircraft. Specifically, this system can collect the complete, polarimetric target scattering matrix as a function of frequency in real time from all three traditional monopulse channels, as well as from the usually terminated diagonal difference channel. The acquired data can be used for multidimensional images, or for studying the characteristics and performance of monopulse trackers following real targets.
Target positioning error effects on RCS magnitude and phase responses in ISAR data
G. Fliss (Environmental Research Institute of Michigan),I. LaHaie (Environmental Research Institute of Michigan), W. Nagy (Environmental Research Institute of Michigan), November 1992
Coherent subtraction algorithms, such as specular subtraction, require precision target alignment with the imaging radar. A few degrees of phase change could significantly degrade the performance of coherent subtraction algorithms. This paper provides an analysis of target position measurement errors have on ISAR data. The paper addresses how traditional position errors impact phase and image focusing. Target rotational positioning errors are also evaluated for their impact on magnitude errors from specular misalignment and polarization sensitive scattering and image phase errors from height-of-focus limitations. Several tables of data provide a useful reference to ISAR data experimenters and users.
Phased-array testing and diagnostics using planar near-field scanning
K. MacReynolds (National Institute of Standards and Technology),A. Repjar (National Institute of Standards and Technology), D. Kremer (National Institute of Standards and Technology), N. Canales (National Institute of Standards and Technology), November 1992
The Antenna Metrology group of the National Institute of Standards and Technology (NIST), working in cooperation with McClellan Air Force Base (MAFB), Sacramento, CA, have examined-measurement techniques to test a large phased-array antenna using planar near-field (PNF) scanning. It was necessary to find methods that would be useful in both field and production testing and could provide gain and diagnostic information in a simple and timely manner. This paper will discuss several aspects of the PNF measurement cycle that impact effective testing of the antenna array. These aspects include the use of a polarization-matched probe, the effect of scan truncation both on the transform to the far field and the transform to the aperture plane, and use of gain prediction curves as a diagnostic tool.
A Dual-ported probe for planar near-field measurements
W.K. Dishman (Scientific-Atlanta, Inc.),A.R. Koster (Scientific-Atlanta, Inc.), D.W. Hess (Scientific-Atlanta, Inc.), November 1992
A dual-linearly polarized probe developed for use in planar near-field antenna measurements is described. This probe is based upon Scientific-Atlanta's Series 31 Orthomode Feeds originally developed for spherical near-field testing. The unique features of this probe include dual orthogonal linear ports, high polarization purity, excellent port-to-port isolation, an integrated coordinate system reference, APC-7 connectors, and a thin-wall horn aperture to minimize probe AUT interactions. The probe was calibrated at the National Institute of Standards and Technology (NIST) and the calibration data consisting of the probe's complete plane-wave spectrum receiving characteristic s'02(K) were imported directly into the Scientific-Atlanta Model 2095/PNF Microwave Measurement System. This paper describes the dual-ported probe and its application in a planar near-field range.
Dual polaized constant beamwidth RCS reflector antenna
S. Hendler (Israel Aircraft Industries),G. Lazar (ECI Telecom Ltd.) S. Shammas (Israel Aircraft Industries), November 1992
A reflector antenna has been designed for the RCS measurements. The antenna is dual linearly polarized and exhibits constant beamwidth over an octave bandwidth. The design principle has been to keep the effective antenna aperture constant in terms of the wavelength over an octave bandwidth. The theoretical design lead into the choice of the antenna and the feed. The reflector was an offset parabolic reflector. The feed was a ring-loaded conical corrugated horn. The measurement results of the designed reflector antenna showed very good agreement with the computer results. The V- and H- polarization characteristics of the antenna are almost identical.
Ground-to-air RCS diagnostic system
R. Harris,A. Strasel, B. Freburger, C. Zappala, M. Lewis, R. Redman, November 1993
The initial phase of METRATEK's new Model 300 Radar System has been installed at the Navy's Chesapeake Tests Range (CTR) at Patuxent River, MD. This ground-to-air Multimode, Multifrequency Instrumentation Radar System (MMIRS) is a high-throughput frequency-and-polarization agile radar that is designed to drastically reduce the cost of measuring the radar cross section of airborne targets by allowing simultaneous measurements to be made at VHF through Ku Band.
Measurement speed and accuracy in switched signal measurements
J. Swanstrom,R. Shoulders, November 1993
The interdependence of accuracy and speed should be considered when analyzing measurement requirements. Tradeoffs can be made to optimize the measurement when accuracy is of primary importance, or where speed is critical. Several different measurement modes of the HP 8530A Microwave Receiver are presented, each with different measurement speed and accuracy tradeoffs. Examples are given that illustrate which acquisition modes would be appropriate to optimize the acquisition speed and accuracy in a variety of applications
Ground-to-air RCS diagnostic system
R. Harris,A. Strasel, B. Freburger, C. Zappala, M. Lewis, R. Redman, November 1993
The initial phase of METRATEK's new Model 300 Radar System has been installed at the Navy's Chesapeake Tests Range (CTR) at Patuxent River, MD. This ground-to-air Multimode, Multifrequency Instrumentation Radar System (MMIRS) is a high-throughput frequency-and-polarization agile radar that is designed to drastically reduce the cost of measuring the radar cross section of airborne targets by allowing simultaneous measurements to be made at VHF through Ku Band.
Simplified polarization measurements
E. Gordon, November 1993
The mathematical language of wave polarization has been somewhat cryptic; usually involving vectors, tensors, or complex numbers or symbolic equations. By using the Poincare' sphere and dot product multiplication, it is possible to reduce the comutation of wave polarization mathematics to simple trigonometric formulas. Furthermore, visual representation of wave polarization on the Poincare; sphere is straight-forward and simple.
Polarization grids for applications in compact antenna test ranges
M.A.J. van de Griendt,V.J. Vokurka, November 1993
In polarimetric RCS measurements, the cross-polarization levels which are required in the test zone, correspond closely to those which are realizable with most Compact Antenna Test Ranges (CATR). On the other hand, such a performance may not satisfy the accuracy requirements in cross-polarization measurements of high performance microwave antennas. These applications include spacecraft antennas, ground stations for satellite communications or microwave antennas for terrestrial applications, where two polarizations are used simultaneously.
Planar near-field alignment
D. Kremer,A. Newell, A. Repjar, A. Trabelsi, C. Rose, M. Pinkasy, November 1993
This paper will discuss one method of characterizing the scan plane for planar near-field measurements. The method uses a theodolite auto-collimator, a laser interferometer, an electronic level and an optical square. The data obtained using these techniques are first used to make alignment corrections to the scan plane; then new data are used to determine the best fit for the realigned scan plane. The normal to this place is referenced using a permanently placed mirror. In addition, the final data obtained can be used in probe position-correction techniques, developed for planar near-field measurements.
In flight VHF/UHF antenna pattern measurement technique for multiple antennas and multiple frequencies
J.S. DeRosa,D. Warren, November 1993
The Precision Airborne Measurement System (PAMS) is a flight test facility at Rome Laboratory which is designed to measure in-flight aircraft antenna patterns. A capability which provides antenna pattern measurements for multiple VHF and UHF antennas, at multiple frequencies, in a single flight, has recently been demonstrated. A unique half space VHF/UHF long periodic antenna is used as a ground receive antenna. Computerized airborne and ground instrumentation are used to provide the multiplexing capability. The new capability greatly reduces time and cost of flight testing. The design, construction, and calibration of the half-space log-periodic ground receiving antenna is discussed and the ground and airborne segments of the instrumentation are described.
High-polarization-purity feeds for anechoic chamber, compact, and near field test ranges
R. Gruner,J. Hazelwood, November 1993
With the recent use of dual-polarized transmission and reception on communications links, the capability to perform accurate polarization measurements is an important requirement of test-range systems. Satellite antennas are commonly measured in the clean, protected environment of compact and near-field ranges, and a circularly polarized feed/field probe is a primary factor in establishing their polarization properties. The feeds also provide excellent source-horn systems for tapered anechoic chambers, where their circular symmetry and decoupling of the fields from the absorber walls improve the often troublesome polarization characteristics of tapered chambers. Circularly polarized feeds are generally composed of four primary waveguide components: the orthomode transducer, quarter-wave polarizer, scalar ring horn, and circular waveguide step transformer. Linearly polarized feeds omit the quarter-wave polarizer. This paper discusses the design and performance of high-polarization-purity source feeds for evaluating the polarization properties of antennas under test. Circularly polarized feeds have been constructed which operate over 10- to 20-percent bandwidths from 1.5 to 70 GHz. Gain values are generally in the area of 12 to 18 dBi, with cross-polarization isolation in excess of 40 dB. Representative measured data are presented.
New extrapolation/spherical/cylindrical measurement facility at the National Institute of Standards and Technology, A
J. Guerrieri,D. Kremer, T. Rusyn, November 1993
A new multi-purpose antenna measurement facility was put into operation at the National Institute of Standards and Technology (NIST) in 1993. This facility is currently used to perform gain, pattern, and polarization measurements on probes and standard gain horns. The facility can also provide spherical and cylindrical near-field measurements. The frequency range is typically from 1 to 75 GHz. The paper discusses the capabilities of this new facility in detail. The facility has 10 m long horizontal rails for gain measurements using the NIST developed extrapolation technique. This length was chosen so that gain calibrations at 1 GHz could be performed on antennas with apertures as large as 1 meter. This facility also has a precision phi-over-theta rotator setup used to perform spherical near-field, probe pattern and polarization measurements. This setup uses a pair of 4 m long horizontal rails for positioning antennas over the center of rotation of the theta rotator. This allows antennas up to 2 m in length to be accommodated for probe pattern measurements. A set of 6 meter long vertical rails that are part of the source tower gives the facility that added capability of performing cylindrical near-field measurements. Spherical and cylindrical near-field measurements can be performed on antennas up to 3.5 m in diameter.


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