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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.
New class in compact ranges
V.J. Vokurka (Eindhoven University of Technology), November 1981
Compact Antenna Ranges (C.R.) proved to suitable for indoor measurements of antennas of moderate size (up to about 4 feet) in the frequency ranges from 4-18 GHz. Where less accurate measurements are allowed, the upper frequency limit can be as high as 60 GHz in current C.R. design. Dimensions of such a range are approximately 4 times larger (in linear dimension) than those of the test antenna. This is due to the face that there is a considerable taper in the amplitude over the aperture of the C.R. Considerable improvements in the electrical performance may be expected for ranges in which two crossed parabolic cylindrical reflectors are used. Due to the increased focal length the uniformity of the amplitude distribution across the final aperture is increased considerably compared to conventional design. Furthermore, an asymmetrical plane-wave zone can be created which makes it possible to measure the patterns of asymmetrical antennas or devices including the direct environment (antennas on aircraft or spacecraft). A compact range which consists of a main reflector with overall dimensions of 2x2 metres has been used for experimental investigation in the 8-70 GHz frequency band. At 10 GHz the plane-wave zone has a slightly elliptical shape (100x90cm). The amplitude variations are in this case less than 0.3dB; the corresponding phase errors are less than 4 degrees. It has been shown that the reflectivity level can be kept below –60dB. Only a minor degradation in performance was found at 70 GHz. In conclusion, the performance of this new compact range is as good as, or better than that of most outdoor ranges. The upper frequency limit is about 100 GHz for ranges of moderate size (up to 3 metres). Summarizing, the main advantages compared to other compact ranges are: -Larger test zone area (up to 2x) for the same C.R. reflector size -better crosspolar performance -considerably higher upper frequency limit The last-named is due to the cylindrical reflector surfaces, which are easier and cheaper to manufacture than double-curved surfaces.
A Microwave interferometer technique for RCS and phase measurements
C. Coy,E. Lette, November 1982
The radar scatter matrix can be accurately characterized in magnitude, relative phase, and polarization for both far-field monostatic and bistatic conditions by means of a microwave interferometer. A separate transmitting antenna illuminates the target of interest while two adjacent receiving antennas measure magnitude and the combine in a phase comparator whose output is a phase differential caused by a changing target aspect angle. Using correct constants and scale factors this differential is integrated to provide target phase information. Different polarizations are obtained by switchable feeds. The technique can be used on an RCS range under static conditions or under dynamic conditions with a ground based radar and an airborne target. The advantage gained is that errors due to radar path length changes are eliminated.
Antenna pattern measurements of large aperture, low sidelobe space antennas
R.L. Haupt (Rome Air Development Center),M. O'Brien (Rome Air Development Center), November 1982
There is a growing interest, for developing large, high performance communication antennas for use in space. Such antennas employ many new technologies and are very expensive to design, build, and deploy. These high risk projects require thorough ground testing before becoming operational. Unfortunately, accurately measuring the far field pattern of a large, structurally weak, high performance antenna on the ground is a difficult problem. The antenna’s extraordinary characteristics place severe tolerances on an antenna measurement range. This paper examines many of the problems encountered with measuring the far field pattern of these antennas. Several possible techniques are reviewed and the errors, tolerances, and limitations associated with each technique are analyzed.
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.
Automated wideband, phase coherent polarimetric radar cross section measurements
T.K. Pollack (Teledyne Micronetics), November 1984
This paper describes the equipment, mechanics and methods of one of the outdoor ranges at Teledyne Micronetics. A computer controlled microwave transceiver uses pulsed CW over a frequency range of 2-18 GHz to measure the amplitude, phase and polarization of the signal reflected off the target. The range geometry, calibration and analysis techniques are used to optimize measurement accuracy and characterize the target as a set of subscatterers.
Planar Near-Field Measurements Using Hexagonal Sampling
L.E. Corey (Georgia Institute of Technology),E. B. Joy (Georgia Institute of Technology), November 1984
This paper describes a new planar near-field measurement technique in which near-field data is collected in a hexagonal rather than a rectangular format. It is shown that the hexagonal method is more efficient than the rectangular technique in that a lower sampling density is required and the hexagonally shaped measurement surface is more compatible with most antenna apertures than the conventional rectangular measurement surface.
The New ANSI RF Radiation Exposure Standard: Its Background and Impact
D.E. Hudson (Lockheed Aircraft Service Company), November 1984
This presentation will focus on the recently revised ANSI C95 RF Radiation Exposure Standard. Some of the research background for the new standard will be given, and its impact will be explained. Instrumentation guidelines for measuring potentially hazardous fields will be presented. The possible damaging effects of non-ionizing RF radiation is receiving increased attention in the public eye, and it behooves the practicing antenna engineer to be aware of the potential dangers to health and safety from exposure of RF energy.
Extension of the extrapolation method for accurate swept frequency antenna gain calibrations
A. Newell (National Bureau of Standards),A. Repjar (National Bureau of Standards), S.B. Kilgore (National Bureau of Standards), November 1984
For approximately 10 years the National Bureau of Standards has used the Extrapolation Technique (A. C. Newell, et al., IEEE Trans. Ant. & Prop., AP-21, 418-431, 1973) for accurately calibrating transfer standard antennas (on-axis gain and polarization). The method utilizes a generalized three-antenns approach which does not require quantitative a priori knowledge of the antennas. Its main advantages are its accuracy and generality. This is essentially no upper frequency limit and it can be applied, in principle, to any type of antenna, although some directivity is desirable to reduce multipath interence.
Software and hardware for spherical near-field measurement systems
D. W. Hess (Scientific-Atlanta, Inc.),C. Green (Scientific-Atlanta, Inc.), B. Melson (Scientific-Atlanta, Inc.), J. Proctor (Scientific-Atlanta, Inc.), J. Jones (Scientific-Atlanta, Inc.), November 1984
The following features have been added to the spherical near-field software set which is available for the Scientific-Atlanta 2022A Antenna Analyzer. Gain Comparison Measurement Probe Pattern Measurement and Correction Thermal Drift Correction Spherical Modal Coefficient Analysis Far-Field, Radiation Intensity, and Polarization Display The addition of the probe pattern correction permits antenna measurements to be made at range lengths down to within several wavelengths of touching. The addition of probe polarization measurement permits three antenna polarization measurements to be made and analyzed as well as two antenna polarization transfer measurements. Correction for phase and amplitude errors attributable to thermal drift is accomplished by the return-to-peak method. Reduction of antenna patterns to spherical modal coefficients is an essential feature of spherical near-field to far-field transforms and is offered as an augmentation to antenna design. Far field display features permit the far fields of antennas to be presented in both component and radiation intensity formats, in circular, linear and canted linear polarization components.
Software and hardware for spherical near-field measurement systems
D. W. Hess (Scientific-Atlanta, Inc.),C. Green (Scientific-Atlanta, Inc.), B. Melson (Scientific-Atlanta, Inc.), J. Proctor (Scientific-Atlanta, Inc.), J. Jones (Scientific-Atlanta, Inc.), November 1984
The following features have been added to the spherical near-field software set which is available for the Scientific-Atlanta 2022A Antenna Analyzer. Gain Comparison Measurement Probe Pattern Measurement and Correction Thermal Drift Correction Spherical Modal Coefficient Analysis Far-Field, Radiation Intensity, and Polarization Display The addition of the probe pattern correction permits antenna measurements to be made at range lengths down to within several wavelengths of touching. The addition of probe polarization measurement permits three antenna polarization measurements to be made and analyzed as well as two antenna polarization transfer measurements. Correction for phase and amplitude errors attributable to thermal drift is accomplished by the return-to-peak method. Reduction of antenna patterns to spherical modal coefficients is an essential feature of spherical near-field to far-field transforms and is offered as an augmentation to antenna design. Far field display features permit the far fields of antennas to be presented in both component and radiation intensity formats, in circular, linear and canted linear polarization components.
The Determination of near-field correction parameters for circularly polarized probes
A. C. Newell (Electromagnetic Fields Division),D. P. Kremer (Electromagnetic Fields Division), M.H. Francis (Electromagnetic Fields Division), November 1984
In order to accurately determine the far-field of an antenna from near-field measurements the receiving pattern of the probe must be known so that the probe correction can be performed. When the antenna to be tested is circularly polarized, the measurements are more accurate and efficient if circularly polarized probes are used. Further efficiency is obtained if one probe is dual polarized to allow for simultaneous measurements of both components. A procedure used by the National Bureau of Standards for determining the plane-wave receiving parameters of a dual-mode, circularly polarized probe is described herein. First, the on-axis gain of the probe is determined using the three antenna extrapolation technique. Second, the on-axis axial ratios and port-to-port comparison ratios are determined for both the probe and source antenna using a rotating linear horn. Far-field pattern measurements of both amplitude and phase are then made for both the main and cross components. In the computer processing of the data, the on-axis results are used to correct for the non-ideal source antenna polarization, scale the receiving coefficients, and correct for some measurement errors. The plane wave receiving parameters are determined at equally spaced intervals in k-space by interpolation of the corrected pattern data.
Effects of the alignment errors on ahorn's crosspolar pattern measurements. Application to L-SAT propagation package antennas.
M. Calvo (Universidad Potitecnica de Madrid),J.L. Besada (Universidad Potitecnica de Madrid), November 1984
When low crosspolar pattern measurements are required, as in the case of the L-SAT Propagation Package Antennas (PPA) with less than -36 dB linear crosspolarization inside the coverage zone, the use of good polarization standards is mandatory (1). Those are usually electroformed pyramidal horns that produce crosspolar levels over the test zone well below the -60 dB level typically produced by the reflectivity of anechoic chambers. In this case the alignment errors (elevation, azimuth and roll as shown in fig. 1) can become important and its efects on measured patterns need to be well understood.
Ultra low sidelobe testing by planar near field scanning
K. R. Grimm (Technology Service Corporation), November 1984
An innovative technique has been developed for accurately measuring very low Sidelobe Antenna patterns by the method of planar near field probing. The technique relies on a new probe design which has a pattern null in the direction of the test antenna’s steered bean direction. Simulations of the near field measurement process using such a probe show that -60dB peak side-lobes will be accurately measured (within established bounds) when the calibrated near field dynamic range does not exceed 40 dB. The desireable property of the new probe is its ability to “spatially filter” the test antenna’s spectrum by reduced sensitivity to main beam ray paths. In this way, measurement errors which usually increase with decreasing near field signal level are minimized. The new probe is also theorized to have improved immunity to probe/array multipath and to probe-positioning errors. Plans to use the new probe on a modified planar scanner during tests with the AWACS array at the National Bureau of Standards will be outlined.
Spherical near-field thermal drift correction using a return-to-peak technique
G.B. Melson (Scientific-Atlanta Inc.),D.W. Hess (Scientific-Atlanta Inc.), J.R. Jones (Scientific-Atlanta Inc.), November 1985
Over the long periods of time needed to acquire spherical near-field data, thermal drift of the system can cause errors in the measurement. The effect of thermal-drift can be removed, if it is monitored during the scanning process. This is accomplished by periodically returning the probe to the near-field peak during acquisition. The same point is re-measured upon each return; and the variations in phase and amplitude are used to produce a correction factor which is applied to each point in the near-field data file. This paper describes the return-to-peak method and the correction algorithm. Experimental results will also be presented.
Optimum near-field probing for improved low sidelobe measurement accuracy
J. Hoffman (Technology Service Corporation),K. Grimm (Technology Service Corporation), November 1985
A novel technique for improved accuracy of sidelobe measurement by planar near field probing has been developed and tested on the modified near field scanner at the National Bureau of Standards. The new technique relies on a scanning probe which radiates an azimuth plane null along the test antenna’s mainbeam steering direction. In this way, the probe acts as a mainbeam filter during probe correction processing, and allows the sidelobe space wavenumbers to establish the dynamic range of the near field measurement. In this way, measurement errors which usually increase with decreasing near field signal strength are minimized. The probe also discriminates against error field which have propagation components in the direction of mainbeam steering, such errors may be due to multipath or scanner Z-position tolerances. Near field probing tests will be described which demonstrate measurement accuracies from tests with two slotted waveguide arrays—the Ultralow Sidelobe Array (ULSA) and the Airborne Warning and Control System (AWACS) array. Results show that induced near field measurement error will generate detectable far field sidelobe errors, within established bounds, at the –60dB level. The utility of te probe to detect low level radar target scattering will also be described.
A Desktop-computer-based antenna pattern recorder
A. Geva (RAFAEL),B. Cyzs (RAFAEL), Y. Botvin (RAFAEL), November 1985
In this paper we describe the implementation of an antenna pattern recorder using a desktop digital computer to replace the conventional analog electro-mechanical element. This means that all pattern recorder front-panel controls and charts are displayed on and accessed via the computer’s CRT, keyboard and peripherals. It has all the regular features, e.g. choice of scales, pen up/pen down etc., plus a multitude of additional features, obtained owing to the use of a digital computer, which will later be outlined in detail. In spite of the numerous options available, the instrument is very easy to master, requires no preliminary knowledge of computer operation and programming. It is entirely menu-driven and designed to trap most operator errors while maintaining a user-friendly environment suitable for technician-level operation.
The Measurement of both complex permittivity and permeability of absorptive materials
S. Tashiro (Hewlett-Packard Company), November 1985
Measurement of complex permittivity (er) and permeability (µr), both vector quantities of absorptive materials, has gained increasing importance with expanding use of the RF and microwave spectrum, particularly in communications and electromagnetic countermeasure applications. In addition, the network analyzer has seen increasing use in non-destructive measurements to determine the chemical composition of a sample dielectric material. The method described here is suited for the measurement of complex permittivity and permeability of ansorptive materials. These measurements have been made for years using numerous methods. A conventional technique involves a two-step process using a slotted line or network analyzer. First, the sample is backed up by a short circuit and the input impedance is measured. Next, the short circuit is moved ¼ ? from the sample to simulate an open circuit termination (where ? is the incident signal wavelength), and a second measurement is made. The results of these two measurements are used to solve simultaneous equations for er and µr. This procedure is repeated for each frequency of interest. Uncertainties in the measurement include test set-up frequency response, mismatch, and directivity errors, as well as the uncertainty in the physical position of the short circuit.
Spectral evaluation of reflector surfaces used for compact ranges
E.B. Joy (Georgia Institute of Technology),R.E. Wilson (Georgia Institute of Technology), November 1986
This paper presents the results of a study conducted to determine the effects of reflector surface errors on compact range performance. The study addressed only the reflector surface accuracy and not edge scattering, reflector illumination or reflector size. The study showed that low spatial frequency sinusoidal surface errors are significant contributors to amplitude ripple in the quiet zone field. Simple equations are presented for estimation of quiet zone amplitude ripple due to reflector surface errors. The study also presents measured surface error for two manufactures of reflector panels. The spectral (plane wave) components of the reflected field are displayed for a compact range reflector composed of a collection of these panels. *This work supported by the U. S. Army Electronic Proving Ground, Ft. Huachuca, AZ and the Joint Services Electronics program


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