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As the accuracy of antenna range instrumentation improves, multipath on the range is becoming the key limitation in antenna metrology. A fundamental requirement to improving range performance is the accurate and repeatable characterization of scattering on a range. A promising technique for range characterization is the planewave spectral (PWS) range probe. Earlier papers have demonstrated the ability of the PWS probe to locate multiple scattering centers on a range. Of equal importance to the user is the ability to correctly assess the magnitude of the scattering centers. This paper presents the problem of spectral peak broadening due to phase curvature from localized scatterers. Methods for improving the accuracy of scattering center estimation are presented along with numerical studies of the performance of these methods.
A mini compact range system has been built for NASA, Langley Research Center. The performance of the system was evaluated at the Ohio State University by probing the fields along a vertical cut and a horizontal cut. The probe data showed that the target zone fields contain stray signals, which do not originate from the reflector surface. The probe data was imaged to locate the sources of the stray signal. Both conventional Fourier techniques as well as the MUSIC algorithm were used to image this data. The results of this study are discussed in this paper. It is shown that at the back end of the chamber, the absorber scattering can be quite significant. The aperture blockage due to the feed structure also contributes to stray signals in the target zone.
A spherical range probing technique for the location of secondary sources in far-field compact and spherical near-field antenna measurement ranges are presented. Techniques currently used for source location use measurements of the range field on a line or plane to locate sources. A linear motion unit and possibly a polarization rotator are necessary to measure the range field in this manner. The spherical range probing technique uses measurements of the range field made on a spherical surface allowing the range positioners to be used for the range field measurement. The plane wave spectrum of the measured range field is used for source location in the spherical probing technique. Source locations in the range correspond to the locations of amplitude peaks in this spectrum. Source resolution limits of this technique is illustrated using simulated range measurements. Obtaining a plane wave spectrum from measured data is discussed.
The extraneous signals that perturb antenna patterns can be found and identified by a method known as “longitudinal translation at selected points”. The method is usually applied to certain selected angular points on the antenna pattern. With this technique the composite pattern – consisting of the direct-path signal and the reflection signal – is measured at a series of translation distances along the axis of the antenna range. By utilizing both the amplitude and phase of the received signal, one can remove the signal that results from stray reflection and retain the desired direct path signal. The result is an improved and more accurate version of the pattern. In this presentation I review this technique as specifically applied to compact range antenna measurements, and apply it to several patterns, to demonstrate the method.
A technique is presented for performing vector error corrected measurements of reflection coefficient using an antenna measurement receiver, the Scientific-Atlanta Model 1783, in an automated system. The technique uses an open-short-load calibration implemented in software in the system controller. The technique is simple and accurate. The equations for the measurement are derived and results as compared to the HP 8510B network analyzer are presented.
Antenna measurement accuracy is often not addressed in a rigorous manner. A methodology for projecting antenna measurement accuracy is described together with some of the error components that limit measurement accuracy. Antenna measurement accuracy is approached through an error budget projection, which requires the first and second order statistics of the individual error sources. Typical error sources are described along with methods of obtaining the statistics required for the error budget.
Comparisons of predicted and measured phase and amplitude data have been made for the Model 1640 compact range. The predicted data is generated using either a physical optics model for shaped offset reflectors with a feed model which takes the corrugation depth and spacing into account or a similar geometric optics model. Excellent agreement has been obtained including accurate prediction of the effects of axial feed movement.
This paper summarizes the performance of the new Harris 1612 Compact Range Standard Product. The Harris 1612 is a dual shaped reflector collimator system. Measured data, both amplitude and phase from the 12-foot diameter quiet zone is presented. The quiet zone was characterized using an automated two-way HP8510B based measurement system. The inherent system benefits for both antenna and RCS measurements are also discussed.
This paper describes the techniques applied to a fully automatic computer controlled, HP8510 based, range gated digital data acquisition system used to provide scale modeled large aperture synthesis, evaluation of aircraft blockage effects, array patterns, element cancellation ratios, as well as providing a large accurate data base for radar simulation exercises.
This paper examines the economic justification process for a new Antenna or Radar Cross-Section (RCS) measurement system, and presents the techniques that can be used to determine the financial feasibility of a new system. Specific examples are given that will allow engineers to customize calculations to fit their company's specific accounting methods and labor rates.
This paper presents the productivity improvements that are possible in complex antenna measurements using state of the art instrumentation. The productivity improvement is calculated for a hypothetical antenna, and from this productivity improvement manufacturing cost reductions and payback times are derived.
An overview of non-destructive real-time testing of missiles is discussed in this paper. This testing has become known as hardware-in-the-loop (HIL) simulation because it involves the actual missile hardware.
A new type of rolled-edge compact range reflector was designed and built by McDonnell Douglas Corporation. To minimize diffraction, the reflector contour was designed such that the surface radius of curvature and all its derivatives are continuous everywhere. This was accomplished by summing a parabolic function and two hyperbolic functions which have appreciable magnitude only in the edge-roll region. The bottom edge was treated using serrations.
Limitations of current compact range reflector systems are discussed with an emphasis on the diffracted energy and its effect on quiet zone size and quality. A new prime focus reflector design which minimizes the edge diffraction is presented. Computer predicted performance of this design is contrasted with measured field probe data.
In this paper, a general methodology for data reduction and analysis of wide-band RCS data is discussed. This methodology encompasses normal image processing, clutter removal, and noise filtering. Examples of the usefulness of the approach are presented.
This paper describes two signal processing techniques that have been used to overcome specific problems in a Lockheed Aeronautical Systems Corporation (LASC) indoor compact RCS measurement range. Both techniques are post processing techniques used to enhance the accuracy of RCS vs. Aspect measurements. These two techniques can speed up measurement time, increase measurement accuracy, and increase target sizes on a compact range.
A technique is presented for the measurement of antenna patterns, in which a long, thin wire is moved past the antenna aperture while the changes in reflection coefficient at the antenna feed are recorded. By suitable processing of these data, the antenna pattern can be calculated.
A new method for producing chamber absorber (patent applied for) is described. The absorber makes use of a resistive gradient through the bulk foam in contrast to standard pyramidal and wedge absorbers that use a geometric shaping of bulk uniform resistive material such as foam loaded with carbon. The absorber is a lightweight open cell reticulated foam, with a metallic material coated onto the fibers of the foam, with varying thickness and varying material properties used to produce the electrical gradient.
Analysis and measurement activities to quantify compact range feed/subreflector time domain response are described in this paper. Reflection properties of various components are quantified and their interaction studied. Results indicate that although the feed/subreflector interaction is a factor, reverberation is dominated by instrumentation interaction particularly in the case of small compact ranges.
The construction of a large reflecting surface is invariably a compromise between the technical requirements and what is economically achievable. During the past three years, the compact range team at Harris has learned a great deal about this process. While aligning and testing the Harris Model 1630/1640 Compact Ranges, we have gone through a long learning experience. This paper presents some of the results of that experience.