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Near Field
Automated Near-Field Antenna Test Set for Phased Array Production
D. Staiman (Government Systems Division), November 1979
The AEGIS AN/SPY-1A antenna system is an S-band monopulse phased array system designed for monopulse operation. Its high performance and manifold capabilities have placed stringent demands on the test system used in its evaluation. This paper will describe the AEGIS Near-Field Antenna Test Set (ANFATS) currently being implemented for acceptance testing production models of the antenna, a system designed for operation by manufacturing test personnel
Economy of Near Field Antenna Measurements
G. Hickman (Scientific-Atlanta, Inc.), November 1979
Near field antenna measurements have long been of interest to the antenna community and of particular interest to those in the design and measurement of antennas. Efforts in this area using analog computers for data reduction were already under way in the late 1950’s. These applications were limited, primarily due to the limitations of the analog computer. Two planar near field probe positioners were built by Scientific-Atlanta during this period and delivered; on to Martin Denver and one to the Georgia Institute of Technology. These units were used for development on planar near field measurements. The unit at Martin Denver was also used by the Bureau of Standards. Experimental work at Georgia Tech led to Dr. Joy’s thesis on spacial sampling and filtering.1 This work on sampling was particularly important because it gave an understanding of the required data density for meaningful transformation by digital computer. Numerical integration is a time and core intensive process and it was the utilization of the Fast Fourier Transform in the early 1970’s that made the digital computer a viable approach to the problem.
Spherical near-field antenna measurements with the Scientific-Atlanta Model 2022
Joseph J. Tavormina (Scientific-Atlanta, Inc.),D.W. Hess (Scientific-Atlanta, Inc.), November 1980
Near-field antenna measurement techniques offer an alternative to conventional far-field antenna measurement techniques. Of the various coordinate systems used for near-field measurements, the spherical coordinate system provides the most natural extension from the conventional far-field characterization of an antenna to a more general characterization for arbitrary range lengths. This paper describes the Scientific-Atlanta Model 2022, a user-oriented implementation of a spherical near-field antenna measurement system. An example of typical system usage is provided. System capabilities and performance are described. Key concepts required to understand and use the spherical near-field method are discussed. The advantages and disadvantages of near-field antenna testing in relation to conventional far-field testing are considered. The particular merits of spherical near-field testing as compared to other forms of near-field testing are discussed. Antenna testing situations which provide the most likely candidates for the spherical near-field measurement technique are described.
Near-field measurement techniques and equipment at the NAEC facility
R.L. Staples (Naval Air Engineering Center),J.L. Kunert (Naval Air Engineering Center), November 1980
The Naval Air Engineering Center has been assigned the task of developing Near Field Measurement Techniques and Equipment for testing Navy Aircraft-mounted antennas. These efforts will be applied to Nose-mounted and Wing-mounted antennas. The ultimate objective is the development of a portable near-field test system for the Navy’s ‘O’ level. The test system will produce far field pattern predictions of installed airborne antennas by measuring and processing near field data. NAEC would, also, like the test system to determine if an installed antenna is mission capable or degraded; and in the event of a failed antenna, the test system will isolate the fault of that antenna. This paper will describe NAEC’s progress in this task by descriptions of the following: I. Electrical Hardware i.e. transmitter, receiver, interfaces, controllers II. Mechanical Hardware i.e. translator, probe carriage III. Mathematical approaches Also, recent laboratory results will be described.
Near-field measurement techniques and equipment at the NAEC facility
R.L. Staples (Naval Air Engineering Center),J.L. Kunert (Naval Air Engineering Center), November 1980
The Naval Air Engineering Center has been assigned the task of developing Near Field Measurement Techniques and Equipment for testing Navy Aircraft-mounted antennas. These efforts will be applied to Nose-mounted and Wing-mounted antennas. The ultimate objective is the development of a portable near-field test system for the Navy’s ‘O’ level. The test system will produce far field pattern predictions of installed airborne antennas by measuring and processing near field data. NAEC would, also, like the test system to determine if an installed antenna is mission capable or degraded; and in the event of a failed antenna, the test system will isolate the fault of that antenna. This paper will describe NAEC’s progress in this task by descriptions of the following: I. Electrical Hardware i.e. transmitter, receiver, interfaces, controllers II. Mechanical Hardware i.e. translator, probe carriage III. Mathematical approaches Also, recent laboratory results will be described.
An Automated Precision Microwave Vector Ratio Measurement Receiver Offers Solutions for Sophisticated Antenna Measurement Problems
F.K. Weinert, November 1980
This paper describes a new, automated, microprocessor controlled, dual-channel microwave vector ratio measurement receiver for the frequency range 10 MHz to 18 GHz. It provides a greater than 120 dB dynamic range and resolutions of 0.001 dB and 0.1 degree. Primarily designed as an attenuator and Signal Generator Calibrator, it offers solutions to antenna measurement problems where high accuracies and/or wide dynamic measurement ranges are required such as for broadband cross-polarization measurements on radar tracking antennas, highly accurate gain measurements on low-loss reflector antennas, frequency domain characteristics measurements on wide-band antennas with resulting data suitable for on-line computer conversion to time domain transient response and dispersion characteristics data and wideband near field scanning measurements for computing far field performances. The measurement data in the instrument is obtained in digital form and available over an IEEE-488 bus interface to an outside computer. Measurement times are automatically optimized by the built-in microprocessor with respect to signal/noise ratio errors in response to the measurement signal level and the chosen resolution. Complete digital measurement data amplitude of both channels and phase, is updated every 5 milliseconds.
Antenna pattern interpolation via digital signal reconstruction
J.J. Tavormina (Scientific-Atlanta, Inc.), November 1980
Digital signal processing techniques provide a method by which a finely resolved antenna pattern can be reconstructed from coarsly sampled data. Antenna pattern reconstruction offers several advantages over the direct measurement of a finely resolved pattern, and is applicable whenever a computer is available for implementation of the reconstruction algorithm. As computerized pattern measurement equipment becomes more prevalent, pattern reconstruction algorithms will become more common place. The advantages of pattern reconstruction include higher quality presentation of antenna patterns due to increased resolution, decreased data acquisition time due to coarser sampling, and decreased data storage requirements. The mean square error or a reconstructed antenna pattern is smaller than that of the directly measured pattern. In the context of near-field to far-field pattern transformations, pattern reconstruction becomes essential. The transformation is performed at a coarse spacing for maximum computational speed without compromising the quality of output data. This paper provides an introduction to the technique of antenna pattern reconstruction. Key concepts and terminology are discussed A generic reconstruction algorithm is developed. Examples of interpolated antenna patterns are shown.
Current near-field antenna measurement research activities at Georgia Tech
E.B. Joy (Georgia Institute of Technology), November 1981
Research on the near-field antenna measurement technique is now in its 15th year at Georgia Tech. Current research is supported by the Army Research office, by the Joint Services Electronic Porgram [sic], and the National Science Foundation. An overview of the current research activities will be given including a description of the Georgia Tech Planar, Cylindrical and Spherical Surface near-field ranges. A recently developed technique for analytic compensation of near-field probe positioning error will be presented.
Cylindrical Near-Field Techniques with Application to Array Antennas
V. Jory (Georgia Institute of Technology),Donald G. Bodnar (Georgia Institute of Technology) David F. Tsao (Georgia Institute of Technology), November 1981
A cylindrical near-field antenna range has been designed, implemented and tested recently at the Cobb County Research Facility of Georgia Tech’s Engineering Experiment Station. While Georgia Tech has had an operational planar scanner since 1974 [1], the relocation of a portion of the Experiment Station to an off-campus site, together with the need for measurements of antennas not practical with the existing planar scanner, prompted the addition of a cylindrical near-field range. Provision was made in the range instrumentation for planar-polar and spherical near-field measurements. Computer software was written to effect the conversion from cylindrical near-field measurements to far-field patterns.
Configuration of spherical near-field ranges
D.W. Hess (Scientific-Atlanta, Inc.),Joseph J. Tavormina (Scientific-Atlanta, Inc.), November 1981
In principle, spherical near-field scanning measurements are performed in the same way as conventional far-field measurements except that the range length can be reduced. This provides a natural advantage to scanning in spherical coordinates over other coordinate systems due to the steady availability of equipment. However, special considerations must be given to near-field range design because of the necessity for phase measurement capability, mechanical accuracy and the need to handle large quantities of data. Based on experience with spherical near-field measurements carried out during verification testing of a spherical near-field transformation algorithm, we discuss the practical aspects of constructing a near-field range. In particular we will consider range alignment procedure, engineering of the RF signal path and times for data collection and processing.
Verification testing of a spherical near-field algorithm
D.W. Hess (Scientific-Atlanta, Inc.),Joseph J. Tavormina (Scientific-Atlanta, Inc.), November 1981
Over the past year an extensive set of verification tests has been made on a particular test antenna in order to confirm the design and operation of a spherical near-field algorithm. The measurement checks included data taken at two frequencies at three range lengths, with two coordinate orientations and with two types of probe horns. Comparisons were made against the compact range and among the various spherical near-field tests. In this talk we show examples from this program of measurements and summarize the results which demonstrate the operation of the spherical near-field scanning technique.
A Precision optical range alignment technique
S.W. Zieg (Scientific-Atlanta), November 1982
Spherical near-field testing and other specialized antenna measurements require precise range and positioner alignment. This paper presents a method based on optical techniques to conveniently measure and monitor both range alignment and the positioner axis orthogonality and intersection. The hardware requirements consist of a theodolite and a unique target mirror assembly viewable from either side.
Field probe measurements and stray signal evaluation of a spherical near-field range
D.W. Hess (Scientific-Atlanta, Inc.), November 1982
Just as with far-field or compact ranges, it is important to evaluate spherical near-field ranges with electromagnetic field-probe measurements. Recall that the fundamental motion for utilizing the spherical near-field measurement technique is to permit antenna measurements to be made at short range lengths, relieved from the constraint of the far-field criterion. Just as the illumination function in the test zone of an ideal far-field range is a uniform planar wavefront, the ideal illumination function for a near-field range is a spherical wavefront from an elemental dipole. The field probe measurements provide a quantitative and qualitative assessment of the deviation of either a near-field or far-field range from ideal conditions.
A Simplified technique for probe position error compensation in planar surface near field measurements
E.B. Joy (Georgia Institute of Technology),R.E. Wilson (Georgia Institute of Technology), November 1982
This paper presents the results of research conducted to compensate near field measurements for known errors in near field probe position. The complete solution for probe position error compensation and associated computer algorithm developed by Corey as a Ph.D. dissertation resulted in a large computer memory and computation time requirements. Corey’s results showed, however, that the prime effect of probe positioning error was a change in the near field measurement phase in the direction of main beam propagation. It was also shown that the sinusoidal components of the probe position error produced spurious sideband propagation directions in the calculated far field patterns. This information has been used to develop a simplified probe position error compensation technique which requires negligible computer storage and computation time. An early version of this technique has recently been implemented at RCA for the Aegis near field measurement facility. The technique and sample results are presented for a small probe position errors and for a low sidelobe level antenna measurement.
Millimeter wavelength measurements of large reflector antennas
J.H. Davis (University of Texas at Austin), November 1982
An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9 m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 µm at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation. In addition, important factors which influence the overall error budget have been identified. These include errors in setting the antenna angular position and fluctuation noise in the atmosphere and electronics. An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9 m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 µm at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation. In addition, important factors which influence the overall error budget have been identified. These include errors in setting the antenna angular position and fluctuation noise in the atmosphere and electronics.
Design of a utility precision near field scanner
M.J. Drexler (Physical Science Laboratory), November 1982
This paper explored the details of the mechanical and electrical design of a multipurpose scanner. Planar, cylindrical and spherical scans as well as separation scanning (for extrapolation gain method) are accomplished by allowing any two of the five axes to be selected for program control. Special laser interferometers are available for the X-Y planar scanning. However, all axes are fitted with two-speed synchros. The method of driving and counter-weighing the X-Y probe carriage reduced the moving mass significantly which helps in the areas of start-stop agility, resonances, bearing wear and structual bending.
Antenna calibration at the TUD-ESA spherical near-field range
F. Holm Larsen (Technical University of Denmark),J.H. Lemanzyk (Technical University of Denmark) J.E. Hansen (Technical University of Denmark), November 1983
Since 1976 the Technical University of Denmark (TUD), sponsored by the European Space Agency (ESA), has developed a facility for spherical near-field scanning of antennas. This range has been in operation since April 1979 and has undergone continuous refinement. Some of the measurement results obtained with the facility as well was various aspects of the measuring system itself have been published from time to time (Ref. 1-5).
A Dual-ported, dual-polarized spherical near-field probe
J. R. Jones (Scientific-Atlanta, Inc.),D. P. Hardin (Scientific-Atlanta, Inc.), November 1983
Spherical near-field testing of antennas requires the acquisition of a great volume of data. In general, to compute the far-field of the antenna under test in any direction requires the acquisition of data at sample intervals related to the size of the antenna under test over a spherical sampling surface completely enclosing the antenna under test. This data must also be sampled as a function of probe orientation. Even for the simplest possible case, two probe orientations (or two probes) must be used.
SNFTD - a new computer program for spherical near-field transformation
Flemming Holm Larsen (Technical University of Denmark), November 1983
As a part of the research project in Denmark on spherical near-field measurements, a number of FORTRAN programs for transformation of measured near-field data has been developed since 1976. Based on earlier work by Jensen, Wacker and Lewis, the series of programs can be summarized as follows: SNIFT (1976) Without probe correction based on a program by Lewis, NBS. Small antennas only. SNIFTB (1977) First program with probe correction. Maximum antenna diameter 25 wavelengths due to numerical instabilities. SNIFTC (1978) With probe correction. Numerically stable. Antenna size limited by the requirement that a full sphere of measured data must be contained in core memory during execution. SNIFM (1980) Segmented program with segmentation of data written for a HP1000 computer only. Antenna diameter limited to 120 wavelengths due to certain arrays in addressable memory. The new computer program is based on the experience with spherical near-field measurements at the Technical University of Denmark.
Gain comparison measurements in spherical near-field scanning
D.W. Hess (Scientific-Atlanta, Inc.),J.R. Jones (Scientific-Atlanta, Inc.), November 1983
A set of near-field measurements has been performed by combining the methods of non-probe-corrected spherical near-field scanning and gain standard substitution. In this paper we describe the technique used and report on the results obtained for a particular 24 inch 13 GHz paraboloidal dish. We demonstrate that the gain comparison measurement used with spherical near-field scanning give results in excellent agreement with gain comparison used with compact range measurement. Lastly we demonstrate a novel utilization of near-field scanning which permits a gain comparison measurement with a single spherical scan.


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