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The Slotline/Bowtie Hybrid (SBH) antenna concept has been applied to develop an ultra wide bandwidth feed for compact range applications. The initial design requirements were to develop a feed with a 30 degree 1dB beamwidth from 1 to 18 GHz. It was felt that one could sacrifice the beamwidth at the lower frequencies somewhat because that would reduce the feed spill over which is normally the worst at lower frequencies. The resulting antenna has an 18" by 18" aperture and basically meets the bandwidth requirements. In the worst case, it has 2 dB variation across the desired 30" beamwidth. The phase center is relatively constant, and VSWR is basically less than 2:1 from 1 to 18 GHz. Measured and calculated results are shown to illustrate the performance of this new feed antenna. In addition, the measured amplitude and phase patterns have been input to a reflector analysis code to predict the field probe data in the simulated quiet zone. These results clearly show that this new feed performs very well from 1 to 18 GHz.
Considerable attention has been paid in recent years to 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 describes a new general purpose software package for that analysis. This software has been written to analyze data acquired in a plane-polar configuration. Analysis options include raw data analysis, near-field focusing of single or multiple line cuts, and plane wave spectrum propagation. A graphical user interface gives the operator extensive control over analysis and display parameters. The analysis algorithms used for multiple-cut processing can function with as few as two radial line cuts.
The simultaneous illumination of the Quiet Zone by number of beams is helpful and cost-effective for broadband antenna and RCS measurements. For an application such as, for instance, Electronic Warfare development, the use of scanning beam or multiple beams gives more extensive opportunities for designers. When the antenna-under-test is small in size, the lightweight and small single reflector Compact Range is very well suited for the above applications. Such a Compact Range being moved within the test facility (anechoic chamber or outdoor range) provides additional flexibility for the tests. This paper describes the development of a small Compact Range with a rolled edge reflector and a two-foot diameter Quiet Zone. Analysis of the Compact Range is performed for different feed positions, providing the beam scan in elevation and azimuth with respect to on-axis beam.
This paper reports on the design, fabrication and installation of the first large compact range whose reflector was machined in one piece. The overall size of this reflector is 30 feet high and 43 feet wide and it produces a test zone 18 feet high and 30 feet wide. It features a novel serrated edge design and a unique multi-feed system. This compact range was fabricated under contract to the U.S. Navy and is currently installed at the Pacific Missile Test Range at Pt. Mugu, California.
Recently, super resolution algorithm have been used in radar target imaging to increase the down range and/or the cross range resolution. In the open literature, however, the super resolution algorithms have been applied to simulated targets or very simple targets measured in a test range. In this paper, the super resolution algorithms, namely the hybrid algorithm and the 2-D linear prediction, are applied to more realistic targets. One of the targets is a flat plate model of the F-117 aircraft. The back-scattered fields of the flat plate model were measured in a compact range. The other target is a Mooney 231 aircraft. The aircraft was flown in a circular pattern approximately 10 miles from the radar. It is shown that the super resolution algorithm can be successfully applied to these targets.
Traditional techniques for evaluating the performance of anechoic chambers, compact ranges, and far-field ranges involve scanning a field probe through the quiet zone area. Plotting the amplitude and phase ripple yields a measure of the range performance which can be used in uncertainty estimates for future antenna tests. This technique, however, provides very little insight into the causes of the quiet-zone ripple. NSI's portable near-field scanners and diagnostic software can perform quiet-zone measurements which will provide angular image maps of the chamber reflections. This data can be used by engineers to actually improve the chamber performance by identifying and suppressing the sources of high reflections which cause quiet-zone ripple. This paper will describe the technique and show typical results which can be expected.
Linear probing is used to evaluate test zone quality and detect extraneous field sources on fixed-line-of-sight far-field and compact antenna ranges. Field probing along a line allows the measurement and meaningful display of range field amplitude and phase taper. Since positioners used with far-field and compact ranges are spherical, linear probing requires extra equipment, namely a linear scanner. This paper will present a new technique for generating linear probing data from measurements made with the existing spherical positioners. The steps necessary for implementing this new technique will be presented and demonstrated using measured data.
A Precision Optical Measurement System (POMS) has been designed, constructed and tested for tracking the position (x,y,z) and orientation (roll, pitch, yaw) of models in Boeing's 9-77 Compact Radar Range. A stereo triangulation technique is implemented using two remote sensor units separated by a known baseline. Each unit measures pointing angles (azimuth and elevation) to optical targets on a model. Four different reference systems are used for calibration and alignment of the system's components and two platforms. Pointing angle data and calibration corrections are processed at high rates to give near real-time feedback to the mechanical positioning system of the model. The positional accuracy of the system is (plus minus) .010 inches at a distance of 85 feet while using low RCS reflective tape targets. The precision measurement capabilities and applications of the system are discussed.
This paper presents the feasability (sic) to explore the Focal Plane (FP) of a Compact Antenna Test Range (CATR). We first introduce the interest of getting very fast the Far Field Pattern of an antenna with a 2D modulated scattering array located at the focus of a CATR. Then, we discuss the geometric, electrical and optical constraints involved when using this technique. A comparison with a classical measurement performed at ESA-ESTEC is shown and we conclude by emphasizing the potentialities of this technique.
The idea of developing a large compact range with scanned quiet zone has been adopted by several international organizations (ESTEC, MBB, Ford Aerospace, etc.) and is expected to be an useful (sic) measurement tool. The Front-Fed Cassegrain configuration is likely to present good scanning capabilities due to its long equivalent focal length and the small curvature of both reflectors. However, some kind of degradation in the test zone is expected in the form of phase aberrations as a function of the lateral feed displacement and frequency, as well as an increase of the Xpolar level. In this paper, the phase aberration and the Xpolar component introduced by a non-centered Front-Fed Cassegrain configuration is analyzed in a GO-GO basis. It is found that the scanning concept can be applied up to a certain frequency limit in which a gradual reduction of the quiet zone dimensions is observed as the feed displacement (plane wave scanning angle) is increased.
As many institutions and companies have constructed anechoic chambers in the past few years, there has been little work done to codify the specification requirements. Often chambers have been constructed from woefully inadequate specifications resulting in chambers that may be too costly, unable to meet the performance criteria, and in some cases, be unsafe. This paper shall present various model specifications and guidelines to properly specify a chamber complex. Compact ranges, tapered chambers, as well as traditional rectangular chambers will all be examined. How to specify absorbing materials and quiet zone sizes, as well as tradeoffs associated with them, will be discussed. Finally, a guide for coping with facility concerns such as civil, structural, RF shielding, HVAC, electrical, and fire protection will be presented. Examples of good specifications and inadequate specifications will be demonstrated and reviewed.
The target support system at Boeing Defense & Space Group's 9-77 Compact Range includes a new string support system. The string support system consists of twelve string reels, six each of the High Capacity String Reels (HCSR). The string reel system is used to suspend and manipulate a target for radar cross section (RCS) measurements, primarily at frequencies below 1.5 GHz. The string reel system is capable of supporting targets up to 10,000 pounds and 40' in length and width. The manipulation and handling of targets, is a major consideration in a RCS measurement test plan. The following paper discusses the newly installed string reel system, enhancements to the 9-77 Range equipment which directly affect the use of the string support system, and future developments planned for the system.
Performance trade-offs are investigated between the use of clustered waveguide bandwidth feeds and the use of one multi-octave bandwidth single aperture feed in a prime focus compact range for dual linear polarization. The results show that feed structure may be used for advantage for the particular test requirements of compact range systems for Radar Cross Section Measurement.
Knowledge of the field character in a range is essential to the understanding of measurements performed. Field probe systems are commonplace for small compact ranges. Outdoor ranges have their systems and methods. A large compact range has unique needs. Available systems are not only fairly expensive, but normally time consuming to install. The McDonnell Douglas Technologies facility implemented a probe system designed to meet the particular needs of the facility.
This paper describes the target handling system that was developed for use in the compact range facility at the University of Pretoria. The system was locally designed and manufactured and comprises of a lift platform, RCS pylon and utility trolley. The pylon utilises a unique design approach resulting in a structure with very high stiffness and surface finish.
This paper will show that it is possible to make bistatic measurements in a compact range environments using near field scanning. A test scanner is designed and operated. Criteria for the accuracy of positioning and repositioning are presented. Algorithms for the transformation of the raw data into bistatic far field calibrated RCS are presented. Examples will be presented where comparisons with theoretical bistatic sphere data are shown. Bistatc pedestal interaction terms will be demonstrated.
The radar cross section (RCS) of a target depends on nature environment as well as many physical variables. The objective of a compact range is to exclude environmental effects on RCS measurements of a target. It is also true for time gated RCS measurements as well. RCS obtained in above manners is more suitable for a space borne than for a ground based target. The contribution from surrounding environment is an inseparable part of RCS for a ship, truck, bridge, and building. We need a suitable method to characterize RCS of a ground based target and its dependence on the environment. The uncontrollable natural change makes environmentally dependent RCS results difficult to compare for a ground based target measured at different time instants. A way to reduce the uncertainties induced from changes is to exhaust all possible RCS measurements before the change. A measurement of this kind is referred to as a concurrent RCS measurement, which in a sense is equivalent to take an optical picture of a rapidly changing object with a strobe light. The step frequency radar located at Chesapeake Bay Detachment of Naval Research Laboratory is such a radar, which is equivalent to at least 45 single frequency radars operating simultaneously from 2.0-18.0 Ghz. Last year, we briefly mentioned this radar in our presentation. We will make a detail discussion of this radar and its capability on concurrent RCS measurements.
Edge and corner diffraction and non-planewave illumination both cause measured free space relativity data to deviate from the infinite sample/planewave result which is predicted when using the Transmission Line Methos (TLM) for planar surfaces. The amount by which each of the two factors perturbs the measured data depends on the measurement system used; compact ranges, near field focused antennas and far field antennas on an NRL arch are all susceptible to the effects of non-planewave illumination and perimeter diffraction. Perimeter diffraction is virtually eliminated in the case of a near field focused system or where the sample is semi-infinite; however, the truncated illumination inevitable yields additional angular planewave components. In a far field system, the quadratic phase variation at the sample surface is shown to cause significant errors in the depth of resonant nulls. A uniform illumination is required to accurately map the depth of resonant nulls, but the consequent perimeter diffraction causes errors in null position. Perimeter diffraction does not cause errors in the null depth providing the illumination in uniform.
An alpha-beta-gamma (a-ß-?) tracking algorithm has been devised to improve the performance of a laser-references planarity control servo. GTRI is developing a field probe for the USAEPG Compact Range at Ft. Huachuca, Arizona. The probe scans a surface whose planarity is controlled by a servo. A reference plane is generated by sweeping a laser beam with a pentaprism. The beam is detected by a photodiode mounted with the probe. The servo nulls any error detected. The servo must correct dynamic errors in the presence of high frequency electronic noise and low frequency atmospheric scintillation. A control algorithm based on the alpha-beta-gamma tracker has been developed and tested by simulation. The algorithm and simulation results are presented.
The target designer using a compact range to verify the predicted RCS of his target needs to know what measurement errors are introduced by the range. The underlying definition of RCS assumes that the target is in the far-field, in free-space, and illuminated by a plane wave. This condition is approximated in a compact range. However, to the extent that these conditions are not met, the RCS measurement is in error. This paper, using the results of the preceding companion paper1, formulates an error budget which shows the typical sources that contribute to the RCS measurement error in a compact range. The error sources are separated into two categories, according to whether they depend on the target or not. Receiver noise is an example of a target independent error source, as are calibration errors, feed reverberation (“ringdown”), target support scattering and chamber clutter which arrives within the target range gate. The target dependent error sources include quiet zone ripple, cross polarization components, and multipath which correspond to reflections of stray non-collimated energy from the target which arrives at the receiver at the same time as the desired target return. These error contributors depend on the manner in which the target interacts with the total quiet zone-field, and the bistatic RCS which the target may present to any off-axis illumination. Results presented in this paper are based on the design of a small compact range which is under construction at RRI. The results include a comprehensive error budget and an assessment of the range performance.