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Accuracy

Improving the accuracy of the planar near-field far-field transformation by a proper choice of integration algorithm and grid
M.S.A. Sanad (University of Manitoba),L. Shafai (University of Manitoba), November 1986

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 [1]. In this paper the aperture field integration method is studied, where the far field components can be calculated from [1] - [2].

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

Measurement of doubly curved reflector antennas
S.H. Lim (Andrew Antenna Company Ltd.),R. Boyko (Andrew Antenna Company Ltd.), November 1986

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.

Automated three-antenna polarization measurements using digital signal processing
J.R. Jones (Scientific-Atlanta, Inc.),D.E. Hess (Scientific-Atlanta, Inc.), November 1985

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
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.

Very broadband measurements of time-varying background returns for a compact radar cross-section measurement range
J.D. Young,E. Walton, P. Bohley, November 1985

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
H.P. Cotton (Georgia Tech Research Institute),C.H. Green (Georgia Tech Research Institute), D.H. Harrison (Georgia Tech Research Institute), J.L. Estes (Georgia Tech Research Institute), R.A. Gault (Georgia Tech Research Institute), November 1985

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
M.L. Guenther (Scientific-Atlanta Inc.),J.B. Wilson (Scientific-Atlanta Inc.) Charles H. Currie (Scientific-Atlanta Inc.) Robert C. Hyers (Scientific-Atlanta Inc.) Vincent M. Franck (Scientific-Atlanta Inc.), November 1985

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.

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.

A Dual shaped compact range for EHF antenna measurements
J.K. Conn (Harris Corporation),C. L. Armstrong (Harris Corporation), L. S. Gans (Harris Corporation), November 1984

A dual offset shaped reflector compact range is described. Improvements over the traditional single reflector, apex-fed compact range are outlined and discussed. A design plan for a dual offset shaped reflector compact range for EHF antenna measurement is presented.

G/T measurement of highly directive antenna systems
G.M. Briand (Harris Corporation), November 1984

A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.

VHF antenna range design
C. J. Chen (Rockwell International Corp.), November 1984

The design concept for outdoor antenna ranges operated at frequency 50 MHz is discussed. The antenna range is designed for test of VHF antennas mounted on a full-scale satellite mockup. Due to the large size of test objects, a tradeoff between cost and test accuracy among carious range configurations is addressed. Due to near-omni directional characteristics of test antennas, the multipath interference may be severe. The interference ground reflection, surface wave and multiple scattering are quantified and evaluated.

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.

A Figure of merit for evaluating signal processing antennas
E. Jacobs (Aerospace Corporation), November 1984

In recent years a new class of reflector antennas utilizing array feeds has been receiving attention. An example of this type of antenna is a reflector utilizing a moveable array feed for beam steering. [1]-[3]. Due to the circuitry required to adjust the weights for the various feed array elements, an appreciable amount of loss can be introduced into the antenna system. One technique to overcome this possible deficiency is to place low noise amplifiers with sufficient gain to overcome the weighting function losses just after each of the feed elements. In the evaluation of signal processing antennas that employ amplifiers the standard antenna gain measurement will not be indicative of the antenna system’s performance. In fact, by only making a signal measurement, the antenna gain can be made any arbitrary value by changing the gains of the amplifiers used. In addition, the IEEE Standard Test Procedures for Antennas [4] does not cover the class of antennas where the amplifier becomes part of the antenna system. There exists a need to establish a standard of merit or worth for multi-element antenna systems that involve the use of amplifiers. This communication presents a proposed figure of merit for evaluating such antenna systems.

A New antenna test facility at General Electric Space Systems Division in Valley Forge, PA.
R. Meier (General Electric Co.), November 1984

This paper describes the new antenna test facility under construction at General Electric Space Systems Division in Valley Forge, PA. The facility consists of a shielded anechoic chamber containing both a Compact Range and a Spherical Near-Field Range. In addition, it provides for a 700’ boresight range through an RF transparent window. The facility will be capable of testing antenna systems over a wide frequency range and will also accommodate an entire spacecraft for both system compatibility and antenna performance tests.

Using the HP 8510 network analyzer to measure the radiation patterm of a dipole antenna using time domain and gating to remove the effects of ground clutter
J. W. Boyles (Hewlett-Packard Company), November 1984

A classical problem encountered when measuring the far-field radiation pattern of an antenna in a medium-distance range is the degradation that occurs when undesirable reflections (from the ground or nearby objects) are present. To reduce this problem, the source and test antennas are often installed on towers to remove them from the reflective objects, RF absorptive materials are used to reduce the magnitude of the reflected signals, and often the reflective objects in the range are adjusted in order to null out the reflections and “clean up” the range. These solutions are often limited in their effectiveness and can be prohibitively expensive to implement.

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.

A High speed, high accuracy position indicator
S. Nichols (Scientific-Atlanta), November 1984

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
W.D. Burnside (Ohio State University),B. M. Kent (Air Force) M. C. Gilreath (NASA), November 1984

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.

Transmission Lines/Antenna Systems Analysis
A.M. Madni,L.A. Wan, November 1983

A new technique with utilizes Digital Signal Processing algorithms in conjunction with Frequency Domain Reflectometry (FDR) to characterize transmission line system is discussed. Algorithms are developed which include tbe Windowed Fast Fourier Transform (WFFT) to determine the location and amplitude of single or multiple mismatches in a single pass. Refinement techniques include quadratic interpolation for increased location and amplitude accuracy and correlation for rejecting harmonics and high power “foreign” (interference) signals.







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