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Compact range systems have been widely used for antenna measurements. However, the amplitude taper can lead to significant measurement errors especially as the dimension of antenna is larger than quiet zone area. An amplitude taper removing technique by software implement is presented for compact range system. A 12 feet by 1.0 feet S-band rectangular slot array antenna is measured in SA5751 compact range system, which provides a quiet zone area with a 4 feet diameter. Results of corrected far-field patterns from compact range are compared with that taken by planar near-field range.
It has been recently shown that an optimized blended rolled-edge compact range reflector can be successfully used to measure two or three foot targets at microwave and millimeter frequencies. In addition to the reflector design, one is faced with many other practical range design issues, such as absorber treatment, target mount and access, feed mount and access, etc. Each of these design aspects has been evaluated and an actual range has been constructed to illustrate the capability of such a system. The feed is mounted on a rotating side door for easy access. The target zone is approached from the rear of the chamber by rotating the backwall. These design concepts allow the range operator to quickly modify the measurement setup, yet still maintain extremely stable results. The simplicity of this design as well as its excellent measurement capability are presented.
Since the first commercial compact range was introduced by Scientific-Atlanta in 1973, the compact range has become a very popular alternative to far-field ranges. In recent years larger and larger compact ranges have been built, increasing the size of antennas that may be tested and lowering the operating frequency. However little has been done in the other direction, to increase the operational frequency and to decrease the size of the compact range. This paper reports on the design and fabrication of a small compact range having a 1 foot test zone and operating at 95 GHz.
A performance simulation for analyzing the measurements of target RCS in a compact radar range has been applied to a small indoor range which will be installed at RRI. A dual reflector collimator has been examined with respect to both quiet-zone quality and the amount of stray energy in the chamber which eventually end up as clutter or multipath interference. The complicated ray geometries, beyond the reach of hand calculation, are discovered by complete tracing of all the rays from the feed source. The ray pats which interfere with target measurements are shown convincingly by graphical display. Vector clutter subtraction is widely used in compact ranges in order to reduce the background clutter to an acceptable level. Some of the effects which limit the effectiveness of clutter subtraction are also addressed in the paper. The sources of measurement errors which are obtained by this simulation are used in the measurement-error budget analysis, which is the subject of the follow-on paper.
Shaped beam illumination of a parabolic, circular aperture compact range reflector using a multi-ring planar array feed is investigated. Since no reflector edge treatment is employed, the entire parabolic surface is available for ray collimation. A technique is presented for the design of array feeds which result in a reflector illumination which is uniform with a specified ripple in the central portion, but zero at the rim in order to eliminate the first order edge diffracted field. Since the excitation coefficient of each element on a ring is constant and real-valued, no complex phase shifts are required, so that a simplified and cost-effective feed network implementation is possible. The quiet zone field is evaluated for arrays comprised of two, three, and four rings of elements. It is demonstrated that the quiet zone field amplitude taper and ripple can be optimized for a specific measurement application by adjusting the amplitude distribution among the rings. Performance is compared with that of a serrated reflector configuration. The array sidelobe level and physical size are examined with regard to overall system integration and implementation.
Multiple mechanisms for the generation of extraneous signals exist in a compact range. These include edge diffraction, scattering from surface imperfections, direct feed radiation, and scattering from absorber or other objects in the range. The field quality in the quiet zone is the resultant of the direct signal and these multiple scattering mechanisms. Since the scattering mechanisms are independent, their effects are often modeled independently and statistically combined to yield an estimate of quiet zone field quality. This paper examines the statistics of multiple independent extraneous signals in a compact range. It is shown that the amplitude ripple produced by an extraneous signal computed as the root sum of the squares (RSS) of the individual extraneous signals does not correctly predict the final quiet zone amplitude ripple. Theoretical results for scattering from multiple thin gaps in the surface of a compact range are presented and statistical computer models are used to demonstrate the computation of the resultant compact range quiet zone.
Large Compact Antenna Test Range (CATR) reflectors are often made up of accurate individually fabricated panels which results in interpanel gaps. The electromagnetic scattering produced by these gaps may cause a degradation of the quiet zone performance. An analytical approach coupled with experimental determination of a key new parameter, the magnetic induced field ratio (MIFR), has been developed to evaluate the effect of the scattering from the interpanel gaps. Depending upon the gap scattering assessment, a decision has to be made whether or not to have the gaps filled. Furthermore, these panels are often painted for aesthetics and to protest against corrosion. Therefore, the effects of paint on the panel has to also be addressed. A novel technique of gap treatment and its evaluation is described.
Measurements in the compact range system are susceptible to errors. Some of these errors are caused by chamber stray signals illuminating the target such as sidewall, backwall, ceiling and floor scattering. One of the major source of these stray signals is the feed spillover or the feed/subreflector spillover in a dual reflector system where the feed/subreflector is not isolated from the main chamber. Due to the limited chamber size, some of these errors cannot be eliminated by either hardware gating or software processing. An alternative approach to reduce these errors is by use of a feed cover such that the spillover field is highly attenuated before it can reach the target or chamber clutter sources. The feasibility of using feed cover in a compact range system to reduce the feed spillover has been studied in this paper. The effectiveness and problems associated with using a feed cover have been investigated in terms of numerical simulation and experimental measurements.
A panelized 56 by 50 foot compact range reflector with a wrap-around rolled edge treatment was installed in an anechoic chamber. Good quiet zone performance required that the as-built surface precisely follow the theoretical cosine blended contour. Commercially available CAD/CAM software served as the design platform for development of the overall system layout, rolled edge panel designs and the CNC milling machine source code for contour machining the rolled edge panels. Formed aluminum and machined composite panel fabrication techniques are described, and resulting aggregate surface accuracies as good as 1.0mil rms are presented. The use of multiple triangulating theodolites, photogrammetric measurements with peak accuracies of 0.5 mils, and custom bestfitting software used in surface alignment are described.
A code based n Geometric Optics, but applicable to diffuse surface scattering, it is evaluated for prediction of downrange high range resolution (HRR) plots of signatures generated in a compact range. A description of the technique is given, including physical justification, underlying assumptions, and flexibility of implementation. Data collected at the Hughes Compact Range will be presented in support of the analysis. Usefulness of this code in generating tradeoffs for compact range designs is demonstrated. Variations in the performance of the compact ranges are shown as a function of various range design parameters, including horn performance, chamber length, and target/wall interaction. Results are analyzed and presented in space and time domains.
A compact antenna range has the potential capability of accurately testing antennas larger than the quiet zone specified by its manufacturer. This expansion of the quiet zone can be achieved by using an analytically derived “Gain Correction Factor (GCF)” for a specific antenna under test (AUT). This GCF should be added to the gain measured in the range. A validation testing of the GCF for a 90” antenna at 44.5 GHz was successfully conducted. The antenna gain, sidelobe and axial ratio were measured in a compact range with a 4’x4’ quiet zone and in a larger range with a 12’ x 8’ quiet zone. The difference in gain was compared to the derived GCF and excellent agreement was achieved. The differences between first sidelobes and axial ratios were negligible.
In the present work, different configurations of reflector systems for indoor antenna and RCS measurements have been studied and compared. These include the Single Offset reflector, Dual Parabolic Cylinder configuration, Shaped Cassegrain, Front-fed Cassegrain and Dual Chamber Gregorian. The above comparison between the different systems is made in terms of: Configuration efficiency; Cross Polar level introduced by the reflector configuration; Scanning capability; ratio of the configuration equivalent focal length to main reflector aperture diameter and ratio of subreflector area to main reflector area; RCS background levels; phase errors due to reflectors surface roughness as a function of the frequency. In order to illustrate the above discussion, several examples of commercially available compact ranges (S.A., March, Harris) are examined, as well as some recently developed European facilities (MBB, ESTEC, RYMSA). As it will be shown, each configuration is best suited to satisfy different user requirements. For example Shaped Cassegrain/Gregorian configurations seem to be the most efficient for RCS measurements whereas the Front-fed Cassegrain quiet zone can be scanned with low degradation.
The new Compact Test Range at Dornier GmbH, operational since early 1990, is presented. The system is designed for both antenna and RCS measurements, for support of in-house projects as well as for third party measurement needs. Great emphasis has been on improving measurement through put to reduce effective measurement costs. The major system components are evaluated (anechoic chamber, compact range reflector system, RF instrumentation, positioner system, computer system and measurement software). System specifications, and where possible measured performance data are presented. Finally a typical antenna and RCS measurement are described to get an idea of possibilities together with required range time.
The Concept of Compact Test Range has been recently much used for antenna testing facilities, its main characteristic of having far-field conditions in a small and closed place, for a very large frequency band, makes it very attractive. Antenna manufacturers are building them up when the millimetric waves and the spacecraft flight model antennas become part of their activities. The change of the point of view of the antenna characteristics – now, parameters like Gain and Radiation Patterns are replaced by EIRP, Flux Density or Coverage- modifies the classical test philosophy. It makes different the Test Procedures which, in addition, have to take into account the cleanliness and the quality control required for handling flight models, as well. The Compact Payload Test Range (CPTR) in ESTEC shows up a PWZ of 7 x 5 x 5 metres for a frequency range from 1.5 to 40 GHz.; it has been created for testing whole Spacecraft Payloads in space required cleanliness area. The particular properties of the CPTR as such as shielded room, feed scanning, multiaxis test positioner, etc. are used to improve its test possibilities.
Recently, super resolution techniques have been applied to image spurious signals in compact range measurement systems. These techniques include parametric modeling of the probe data as well as eigen-space based methods. In these techniques, in incident signals on the probed aperture are assumed to be planar, which may or may not be true. In general, if the separation between a signal source and the probed aperture is more than , where D is the size of the probed aperture, one can assume that the signal incident on the probed aperture is nearly planar. It is shown that this is not necessarily true for super resolution techniques. The signal level also affects the minimum distance requirements. The stronger the signal, the farther its source should be from the probed aperture to achieve the optimum performance.
Accurate scattering and antenna measurements require excellent plane wave purity in the target zone; however all measurement systems are contaminated by various stray signals which result in measurement errors. In this paper, a technique of evaluating the stray signal sources in a compact range using a diagonal plat plate as a test target is presented. The scattering cross section of the diagonal flat plate as a function of frequency and angle of rotation is first measured. Then the time domain response for each projection angle is processed to obtain a two dimensional ISAR image of the plate as well as the stray signals. From the stray signal images, the location and relative strength of the stray signals can be determined. Experimental results from the OSU/ESL Compact Range Facility are presented to demonstrate this stray signal imaging technique.
Much research has been done recently on the interpretation of measured field probe data in order to locate and quantify error sources present in the quiet zone of a compact range. This paper examines an alternative method of analyzing those data by applying spherical phase offsets to focus the field probe data to near-field distances. This method is applied to simulated field probe data for a large compact range. The technique yield the correct [x,y,z] coordinates of multiple scattering sources deliberately introduced into the simulated data.
Based on the complexity of the scattering mechanisms associated with a real-world target, it is obvious that measurement diagnostic tools are extremely helpful. On technique that has found great success in this regard is the conventional ISAR or down range/cross range image. However, the results are basically two-dimensional, which limits the usefulness of the data in that most real-world targets have significant three-dimensional features. A very efficient class of 3D image algorithms has been developed which are based on various time domain look angles relative to the target [1]. It has been shown that one can use multiple feed antennas in a compact range to collect this data and then process it directly to obtain a 3D image of the target. This can be done very rapidly, say every 10 seconds, using an approximate solution, or in 10 minutes using a 3D ISAR approach. The system design and techniques used to implement this system are presented in this paper.
This paper demonstrates the performance of the McDonnell Douglas Technologies Incorporated (MDTI) Compact Range A. This HP8510B network analyzer based system utilizes a R-card treated prime focus main reflector in a tandem with broadband 2-18 GHz feeds. A six foot quiet zone can be maintained over the 2-18 GHz bandwidth with no feed or hardware changes, allowing targets to be measured over the full bandwidth in one continuous sweep. Measured data will be presented demonstrating performance features such as quiet zone quality, dynamic range, sensitivity, and image resolution.
Lockheed’s Advanced Development Company (LADC), located in Burbank, California, has been evaluating the capability of indoor anechoic chambers to measure VHF/UHF RCS. Two chambers were available for evaluation. A 155 feet long, 50 feet high by 50 feet wide tapered horn chamber and a compact range having dimensions of 97 feet long, 64 feet high by 64 feet wide, featuring a 46 feet wide collimator. For comparison purposes, a common instrumentation radar was used in each chamber. This radar was based on a network analyzer using a Lockheed designed pulse-gate unit to increase transmit/receive isolation. Various antenna feed system were tried in both chambers to ascertain their characteristics. Theoretical and experimental data on system performance will be presented emphasizing practical implementation and inherent limitations.