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AMTA Paper Archive

Planar near-field measurements of low-sidelobe antennas
M.H. Francis,A. Newell, H. Schrank, J. Hoffman, K. Grimm, November 1993

The planar near-field measurement technique is a proved technology for measuring ordinary antennas operating in the microwave region. The development of very low-sidelobe antennas raised the question whether this technique could be used to accurately measure these antennas. We show that data taken with an open-ended waveguide probe and processed with the planar near-field methodology including the probe correction, can be used to accurately measure the sidelobes of very low-sidelobe antennas to levels of -55 to -60 dB relative to the main-beam peak. We discuss the major sources of error and show that the probe antenna interaction is one of the limiting factors in making accurate measurements. The test antenna for this study was a slotted-waveguide array whose low sidelobes were known. The near-field measurements were conducted on the NIST planar near-field facility

Planar near-field measurements of low-sidelobe antennas
M.H. Francis,A. Newell, H. Schrank, J. Hoffman, K. Grimm, November 1993

The planar near-field measurement technique is a proved technology for measuring ordinary antennas operating in the microwave region. The development of very low-sidelobe antennas raised the question whether this technique could be used to accurately measure these antennas. We show that data taken with an open-ended waveguide probe and processed with the planar near-field methodology including the probe correction, can be used to accurately measure the sidelobes of very low-sidelobe antennas to levels of -55 to -60 dB relative to the main-beam peak. We discuss the major sources of error and show that the probe antenna interaction is one of the limiting factors in making accurate measurements. The test antenna for this study was a slotted-waveguide array whose low sidelobes were known. The near-field measurements were conducted on the NIST planar near-field facility

Demonstration of bistatic electromagnetic scattering measurements by spherical near-field scanning, A
M.G. Cote,R.M. Wing, November 1993

The far-field radar cross section (RCS) of a conducting sphere is obtained by transforming scattered near-fields measured on a spherical surface. A simple and convenient calibration procedure is described that involves measuring the incident field directly at the target location. Although a non probe-corrected transmission formula was used in this study the importance of prove correction in practice is demonstrated.

Demonstration of bistatic electromagnetic scattering measurements by spherical near-field scanning, A
M.G. Cote,R.M. Wing, November 1993

The far-field radar cross section (RCS) of a conducting sphere is obtained by transforming scattered near-fields measured on a spherical surface. A simple and convenient calibration procedure is described that involves measuring the incident field directly at the target location. Although a non probe-corrected transmission formula was used in this study the importance of prove correction in practice is demonstrated.

Planar near-field alignment
D. Kremer,A. Newell, A. Repjar, A. Trabelsi, C. Rose, M. Pinkasy, November 1993

This paper will discuss one method of characterizing the scan plane for planar near-field measurements. The method uses a theodolite auto-collimator, a laser interferometer, an electronic level and an optical square. The data obtained using these techniques are first used to make alignment corrections to the scan plane; then new data are used to determine the best fit for the realigned scan plane. The normal to this place is referenced using a permanently placed mirror. In addition, the final data obtained can be used in probe position-correction techniques, developed for planar near-field measurements.

Planar near-field alignment
D. Kremer,A. Newell, A. Repjar, A. Trabelsi, C. Rose, M. Pinkasy, November 1993

This paper will discuss one method of characterizing the scan plane for planar near-field measurements. The method uses a theodolite auto-collimator, a laser interferometer, an electronic level and an optical square. The data obtained using these techniques are first used to make alignment corrections to the scan plane; then new data are used to determine the best fit for the realigned scan plane. The normal to this place is referenced using a permanently placed mirror. In addition, the final data obtained can be used in probe position-correction techniques, developed for planar near-field measurements.

Analytic spherical near field to near/far field transformation, An
T.K. Sarkar,A. Taaghol, P. Petre, R.F. Harrington, November 1993

An efficient and accurate spherical near field to far field transformation without probe correction is presented. The indices m of the Legendre polynomials is summed up analytically, thereby reducing the computation time. Computations with both synthetic and experimental data illustrate the accuracy of this technique.

Analytic spherical near field to near/far field transformation, An
T.K. Sarkar,A. Taaghol, P. Petre, R.F. Harrington, November 1993

An efficient and accurate spherical near field to far field transformation without probe correction is presented. The indices m of the Legendre polynomials is summed up analytically, thereby reducing the computation time. Computations with both synthetic and experimental data illustrate the accuracy of this technique.

Simplified polarization measurements
E. Gordon, November 1993

The mathematical language of wave polarization has been somewhat cryptic; usually involving vectors, tensors, or complex numbers or symbolic equations. By using the Poincare' sphere and dot product multiplication, it is possible to reduce the comutation of wave polarization mathematics to simple trigonometric formulas. Furthermore, visual representation of wave polarization on the Poincare; sphere is straight-forward and simple.

Simplified polarization measurements
E. Gordon, November 1993

The mathematical language of wave polarization has been somewhat cryptic; usually involving vectors, tensors, or complex numbers or symbolic equations. By using the Poincare' sphere and dot product multiplication, it is possible to reduce the comutation of wave polarization mathematics to simple trigonometric formulas. Furthermore, visual representation of wave polarization on the Poincare; sphere is straight-forward and simple.

An Ultra-wide bandwidth compact range feed antenna
A.L. Sinopoli (The Ohio State University),M. Gilreath (NASA), W.D. Burnside (The Ohio State University), November 1992

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.

A Software package for imaging compact ranges using field probe data
S.T. McBride (Georgia Tech Research Institute),J.L. Bradberry (Georgia Tech Research Institute), November 1992

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.

Small compact range rolled edge reflector for multi-beam applications
M. Winebrand (Orbit Advanced Technologies Ltd.), November 1992

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.

Recent developments in large compact range designs
J.D. Huff (Scientific-Atlanta, Inc.),B. Smith (Scientific-Atlanta, Inc.), J.H. Cook (Scientific-Atlanta, Inc.), November 1992

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.

A High resolution imaging radar for ground-based diagnostic applications
D. Blejer (MIT Lincoln Laboratory),C. Frost (MIT Lincoln Laboratory), H.R. Catalan (MIT Lincoln Laboratory), S. Scarborough (MIT Lincoln Laboratory), November 1992

Lincoln Laboratory has developed a high resolution imaging radar in conjunction with Flam and Russell, Inc. or Horsham, PA. The radar is a highly mobile, ground based system that is capable of two and three-dimensional imaging at very close ranges to a synthetic aperture. The radar is fully coherent from 0.1 to 18 GHz and transmits CW pulses that are stepped in frequency across a preselected bandwidth. High range resolution is achieved by coherently processing the returned signals. The radar is being used for target imaging and for foliage penetration measurements.

An Instrumentation radar system for use in dynamic signature measurements
C.T. Nadovich (Flam & Russell, Inc.),D.R. Frey (Flam & Russell, Inc.), J.F. Aubin (Flam & Russell, Inc.), November 1992

The dynamic, polarization/frequency diverse, Instrumentation Radar System (IRS) described herein combines the features of an X-band radar tracker with a wideband, fully polarimetric coherent data collection system. Mounted in a transportable trailer, the system can be towed to virtually any site to acquire radar signature measurements on moving aircraft. Specifically, this system can collect the complete, polarimetric target scattering matrix as a function of frequency in real time from all three traditional monopulse channels, as well as from the usually terminated diagonal difference channel. The acquired data can be used for multidimensional images, or for studying the characteristics and performance of monopulse trackers following real targets.

Dynamic air-to-air imaging measurement system
R. Harris (METRATEK, Inc.),B. Freburger (METRATEK, Inc.), J. Hollis (The Northrop Corporation), R. Redman (METRATEK, Inc.), November 1992

METRATEK has completed a highly successful program to prove the feasibility of high-resolution, air-to-air diagnostic radar cross section imaging of large aircraft in flight. Experience with the system has proven that large aircraft can indeed be imaged in flight with the same quality and calibration accuracy that can be achieved with indoor and outdoor ranges. This paper addresses the results of those measurements and the Model 100 AIRSAR radar and processing system that were used on this program.

A Portable 3D SAR RCS imaging system
G.B. Melson (GE Aircraft Engines),D.R. Vanderpool (GE Aircraft Engines), November 1992

A portable measurement system has been designed and implemented to produce focused three dimensional RCS images. The Synthetic Aperture Radar (SAR) system was especially designed to operate in harsh physical and cluttered electromagnetic environments. The acquisition system, signal processing and 3D visualization capabilities are discussed and representative data ranging from simple canonical objects to production hardware are presented. The technique meets its design goal in effectively discriminating undesired clutter.

ISAR imaging of aircraft-in-flight using a ground-based radar
A. Jain (Hughes Aircraft Company),I.R. Patel (Hughes Aircraft Company), November 1992

ISAR images and RCS signatures of aircract-in-flight using a ground based and an airborne radar system are presented. The ground-based measurements were at X-band and were of a Mooney 231 aircraft, which flew in a controlled path in both clockwise and counterclockwise orbits, and successiely with gear down, flaps in the take-off position and with the speed brakes up. The air-to-air measurements were made by a radar installed in the nose of the TA-3B aircraft which followed a KC 135 airplane at a range of approximately 450 ft. and traversed a cross-range angle component of (plus or minus) 30(degrees). The data indicates that these systems are useful tools for RCS signature diagnostics of aircraft in flight.

Super resolution radar target imaging of realistic targets
E. Walton (The Ohio State University ElectroScience Laboratory),A. Moghaddar (The Ohio State University ElectroScience Laboratory), I.J. Gupta (The Ohio State University ElectroScience Laboratory), M.W. Tu (The Ohio State University ElectroScience Laboratory), November 1992

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.







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