Extension of the extrapolation method for accurate swept frequency antenna gain calibrations
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.
A High speed, high accuracy position indicator
One of the variables to be quantified when making antenna measurements is position. Without accurate and timely position information, the spatially dependent data cannot be correctly interpreted. Scientific-Atlanta’s 1885 Positioner Indicator and 1886 Position Data Processor offer several improvements in providing position information which can enhance an antenna measurement system. New position indicating techniques have been implemented to allow a higher degree of accuracy and speed than previously attainable. These have been combined with advanced features for automatic system flexibility to create a high performance instrument for many applications. This paper describes the capabilities of these two instruments and how they can be used to improve system performance.
Rolled edge modification of compact range reflector
The compact range is an electromagnetic measurement system used to simulate a plane wave illuminating an antenna or scattering body. The plane wave is necessary to represent the actual use of the antenna or scattering from a target in a real world situation. Traditionally, a compact range has been designed as an off-set fed parabolic reflector with a knife edge or serrated edge termination. It has been known for many years that the termination of the parabolic surface has limited the extent of the plane wave region or, more significantly, the antenna or scattering body size that can be measured in the compact range. For example, the Scientific Atlanta (SA) Compact Range is specified to be limited to four foot long antennas or scattering bodies as shown in their specifications. Note that the SA compact range uses a serrated edge treatment as shown in Figure 1. This system uses a parabolic reflector surface which is approximately 12 square feet so that most of the reflector surface is not usable based on the 4 foot square plane wave sector. As a result, the compact range has had limited use as well as accuracy which will be shown later. In fact, the compact range concept has not been applied to larger systems because of the large discrepancy between target and reflector size. In summary, the target or antenna sizes that can be measured in the presently available compact range systems are directly related to the edge treatment used to terminate the reflector surface.
Automated three-antenna polarization measurements using digital signal processing
In this paper we present a three-antenna measurement procedure which yields the polarization of an unknown antenna to an accuracy comparable to that of the improved method of Newell. The complete method is based on step-scan motion of the two polarization axes on which the antenna pairs are mounted. As a special case this step-scan procedure includes the usual single axis polarization pattern method of polarization measurement.
This three antenna polarization measurement method can be readily automated and is carried out straightforwardly with the assistance of a minicomputer for data acquisition and data reduction. The data reduction method is based on conventional digital Fourier transform techniques and has the advantage of inherent noise rejection. It utilizes a large number of sample points which greatly overdetermine the parameters to be measured.
The method has been verified experimentally with measurements made on multiple overlapping sets of three antennas, as is conventional for this kind of procedure. The data are presented for broad-beam antennas of the type used as near field probe horns.
Optimum near-field probing for improved low sidelobe measurement accuracy
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.
Very broadband measurements of time-varying background returns for a compact radar cross-section measurement range
There are several background return sources on the Ohio State University Compact Radar Range which affect the sensitivity, accuracy, and dynamic range of the measurement. This paper discusses the magnitude and time delay of the principal background “clutter” mechanisms. Next, data on the time drift properties will be presented, and the relation to system temperature and other physical variations will be discussed. Finally, the impact of system design and operation concepts on these performance factors will be discussed.
Automated data acquisition and analysis system upgrade
This paper is a discussion of the upgrade of an automated antenna pattern data acquisition and analysis system located at the U.S. Army Electronic Proving Ground (USAEPG), Ft. Huachuca, Arizona. The upgrade was necessary as the existing facility was inadequate with respect to frequency coverage, data processing, and measurement speed and accuracy. The upgrade was also necessary in view of USAEPG long range plans to automate a proposed large compact range.
A 1-40 GHz synthesized source for antenna range applications
Increased interest in antenna development at millimeter-wave frequencies has contributed to a growing need for signal sources operating to 40 GHz and beyond. The desirable features of such sources include broad frequency coverage; accuracy, stability, and resolution afforded by frequency synthesis; the ability to switch frequencies rapidly; and physical attributes which lend themselves to efficient use in the automated antenna range environment. This paper describes how a recently developed synthesizer meets these requirements. Design approaches used, engineering trade-offs considered, and applications information are presented.
A Method of making fast high accuracy polarization measurements
A method is presented for making fast multi-frequency high accuracy polarization measurements using a digital computer. This paper will provide a brief review of the IEEE standard polarization definitions, their applicability to the three antenna method, and finally a fast two antenna method.  The fast two antenna method uses a dual polarized orthomode sampling antenna along with a standard antenna whose polarization is known. The dual polarized sampling antenna is calibrated before the test data is acquired using the polarization standard in two different orientations 90 degrees apart. Once the calibration data is acquired the dual polarized orthomode antenna is used as a sampling antenna for the AUT.
Since the sampling antenna is dual polarized the AUT polarization data can be obtained rapidly for many frequencies since neither antenna is required to rotate. This method has been used to acquire polarization data for over 500 frequencies in less than 20 seconds.
On the use of the HP-8510 network analyzer for antenna pattern measurements
Enhanced accuracy in antenna pattern measurements using the HP-8510 is possible by using a novel calibration procedure. By circumventing antenna dispersion, this procedure leads to better resolution of multipath responses and thus increases the effectiveness of gated measurements. Measured patterns of a dipole antenna are presented to illustrate the effectiveness of this procedure.
An Automated antenna measurement system using the HP8510
An automated antenna measurement system using the HP8510 is described. The system controls the HP8510, associated signal source, and antenna positioner, to provide a fully integrated, automated test facility. Automation speeds and enhances testing by implementing the following features: - Multiple frequency pattern measurements in a single cut of the pedestal.
- Patterns with rotating linear polarization - Automatic pedestal control - Storage and presentation of fully documented test data.
- Storage and recall of test routines These features complement the premier microwave receiver available today, the HP8510 which offers: - Continuous frequency coverage from .045 to 26.5 GHz - Unparalleled measurement accuracy - 80 dB dynamic range - Time domain gating These features are integrated through software developed using modern software management techniques to form a system which is state of the art in measurement performance, operator interface, and software life cycle supportability.
Reduction of near-field techniques duration
Near-field measurement techniques are widely used today for antenna far-field pattern characterization. Since the 60's, much has been done concerning accuracy. The three main coordinate systems, planar, cylindrical, and spherical have been investigated. probe corrections have been introduced  - .
Improving the accuracy of the planar near-field far-field transformation by a proper choice of integration algorithm and grid
The planar scanning system is commonly used in the near field testing of high gain antennas, where the rectangular measurement grids are used. The polar grids are also used, which are more convenient when the antenna aperture is circular. In the planar scanners the measurements are carried out in the x-y plane in increments of both x and y. The result of the measurement is an mxn matrix of the near field data consisting of m cuts with n data points per each cut. The far field patterns may then be calculated, using the near field data, by the aperture field integration or the modal expansion methods . In this paper the aperture field integration method is studied, where the far field components can be calculated from  - .
Spectral evaluation of reflector surfaces used for compact ranges
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
Measurement of doubly curved reflector antennas
This paper describes the mechanical as well as electrical measurement of doubly curved reflector antennas. The techniques developed for measurement of the new Canadian RAMP Primary Surveillance Radar antenna are described. Instead of a conventional full size template fixture to measure the antenna contour accuracy, an optical twin-theodolite method is used. The problems of the method are discussed and a new simplified analysis for calculating reflector error of doubly curved antennas is presented. Reflector errors are calculated and displayed concurrent with the actual measurements. The measurement of primary and secondary patterns for such antennas are described. Included are brief descriptions of the improved Andrew pattern test range and anechoic chamber facilities.
Antenna pattern correction for range reflections
When performing antenna pattern measurements on far-field antenna test ranges or in anechoic chambers, one of the main problems concerning the pattern accuracy is range reflections. Previous works dealing with this have been limited to the one-dimensional case.
Photogrammetric measurement of antenna reflectors
The application of analytical photogrammetry to the measurement of microwave antenna reflectors is discussed. The basic concepts of photogrammetric triangulation are outlined and accuracy considerations are reviewed. Recent developments in close-range photogrammetric systems, which have greatly enhanced both the accuracy and economy of antenna mensuration, are briefly discussed and advantages of the photogrammetric approach are highlighted. Three recently conducted antenna measurement projects are reviewed.
Precision panel fabrication and measurement
A key element in the performance of the Harris compact range is that the mathematical shaping of the main and subreflector maximizes the percentage of the total radiated energy collimated in the quiet zone. This extra measure of performance doesn't come without an impact on other areas of the design. Specifically, the use of non-geometric shapes means that for large reflectors, where the surface must be segmented for fabrication accuracy, the shape of each segment is unique. Thus, the traditional method of forming each reflector segment, or panel, on a hard surface tool, or bonding fixture, becomes prohibitively expensive for large systems that consist of over a hundred panels in the two reflectors.
The development of an adjustable bonding fixture that can be accurately set to the mathematically defined shape for each panel has made the Harris approach to compact ranges achievable. The use of high accuracy coordinate axis measuring machines to refine and verify the surface of each panel has then made the approach producible. The measurement machines have critical axis accuracies of .0005 inch that provide the capability for verifying .001 inch RMS panel accuracies.
Evaluation of Anechoic Chambers
This paper describes methods commonly used by anechoic chamber manufacturers to characterize chamber performance.
Test procedures depend first on the purpose of the test; second on the purpose of the anechoic chamber and third on the amount of information required.
Most anechoic chambers are built for a specific use. In order to prove its design, the test will be done accordingly. In most anechoic chambers one measures the reflectivity level because this is a measure for the accuracy on future measurements when the chamber is in operation. Anechoic chambers can vary from Antenna Pattern Test Chambers to Radar Cross Section Test Chambers, Electronic Warfare Simulation Chambers and Electro Magnetic Compatibility Test Chambers. Each type of chamber will have its specific evaluation technique.
Some techniques can be done by the chamber user himself. Other methods need some special equipment that will or can only be used for that particular test method.
Some customers want to do their own calibration on a regular basis. They can purchase this special equipment from the chamber manufacturer, if necessary.
More complicated methods make use of computer controlled equipment. The data required can be taken in the chamber. This can be done relatively fast. All sorts of information about the chamber characteristics can be obtained in a later stage in a different format by use of the right software.
This paper gives possible evaluation methods for different types of anechoic chambers. Detailed information about each method can be obtained from Emerson & Cuming.
Antenna diagnosis using microwave holographic techniques on a far-field range
The holographic antenna measurement system developed for the COMSAT Labs far-field range was tested with various antennas including axis-symmetric reflector antennas, offset single and dual reflector antennas, and phased-array antennas. Numerous examples which demonstrate the value of holographic measurement as an antenna diagnostic tool are presented.
Microwave holography utilizes the Fourier transform relation between the antenna radiation pattern and the antenna aperture electromagnetic field distribution. Complex far-field date are collected at sample points and a Fourier transform is performed to give amplitude and phase contours in the antenna aperture plane. These contours facilitate reflector antenna diagnosis. The feed illumination and blockage pattern are provided by the amplitude distribution. The aperture phase distribution allows simple determination of deviations in the reflector surface and feed focusing. For phased-array antennas, the contours provide a measure of the complex element excitation.
Measurement system parameters including pointing accuracy, phase stability, and measurement dynamic range were studied and refinements implemented to increase speed, accuracy, and resolution of the contour plots. To prevent aliasing errors, sampling criteria were explored to determine the optimum parameter ranges. For most antenna positioners, the antenna center is displaced from the rotation center. The importance of properly accounting for this displacement is discussed in the final section.