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Compact Range

Imaging the compact range probe data
I.J. Gupta (The Ohio State University ElectroScience Laboratory),W.D. Burnside (The Ohio State University ElectroScience Laboratory), November 1990

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.

Longitudinal translation at selected points - A measurement technique revisited
D.W. Hess (Scientific-Atlanta, Inc.), November 1990

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.

Comparison of measured and predicted data for the shaped compact range
M.L. Foster (Harris Corporation), November 1989

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.

Performance of a shaped compact range with a 12 foot quiet zone
A.L. Linsay (Harris Corporation), November 1989

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.

Hybrid compact radar range reflector
M.R. Hurst (McDonnell Douglas Missile Systems Company),P.E. Reed (McDonnell Douglas Missile Systems Company), November 1989

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.

Advanced compact range reflector
G.I. Camacho (Brunswick Defense),G.A. Kaiser (Brunswick Defense), November 1989

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.

Post processing corrections to indoor RCS VS aspect measurements
L. Pellett (Lockheed Aeronautical Systems Corporation), November 1989

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.

The Effect of instrumentation VSWR on compact range ringdown performance
G.M. Briand (Harris Corporation), November 1989

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.

Compact range reflector surface accuracy and quiet zone quality
L. Woodruff (Harris Corporation), November 1989

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.

Results of a reflector antenna surface distortion measurement using microwave holography with enhanced imaging
S.W. Gilmore (The Ohio State University ElectroScience Laboratory),R.C. Rudduck (The Ohio State University ElectroScience Laboratory), November 1989

A microwave holographic analysis system is shown to have successfully resolved the surface deformations on an 8' symmetric Cassegrain reflector antenna known to have significant surface deformation problems. The technique is based on the Fourier transform relationship between the aperture field of an antenna and its radiated far-zone field. A signal processing technique dubbed "pattern simulation and subtraction" is discussed that increases the resolution in the transformed aperture domain by removing unwanted signals from the aperture distribution. Measurements taken on the Cassegrain reflector at 11 GHz in the OSU-ESL Compact Range provided excellent amplitude and phase stable data to be processed by the holographic analysis system. Surface deformation profiles generated by this system were then compared to an optical measurement of the main reflector surface. Excellent agreement was obtained with a worst case deviation in the adjusted profiles being 0.05 ?.

Pattern, gain and temperature measurements of reflector antennas
R.C. Rudduck (The Ohio State University ElectroScience Laboratory),K.M. Lambert (ANALEX Corporation), T-H. Lee (The Ohio State University ElectroScience Laboratory), November 1989

An overview of results are presented for far field pattern, antenna gain and antenna temperature measurements of reflector antennas in several frequency bands. The pattern and gain measurements were taken in the compact range at The Ohio State University. The dynamic range available, which gives the ability to take a full 360 degree pattern, and the relatively high speed at which data is collected, are major advantages for pattern and gain measurements in the compact range. In a series of related measurements an 8-foot diameter Cassegrain reflector was used for antenna temperature measurements under clear weather conditions in an outdoor environment.

A Portable compact range
M.C. Li (Naval Research Laboratory), November 1989

Compact ranges are special facilities, requiring a huge anechoic chamber and a large RF reflector to test a full size aircraft. These facilities are expensive and fixed structures, consequently they remain essentially research and design tools. However, as more and more aircraft are being made from composite materials, manufactures with high production volumes may be justified in having a compact range for purposes of quality control. The RF characteristics of these aircraft will change during their useful life cycle. The high cost of compact ranges will deprive most service and maintenance centers from owning one of these unique facilities, and force them to compromise the RF specifications of those aircraft in service. There is a definite need for a low cost and portable compact range. We present the design concept for such a range, whose reflector is divided into several identical pieces while the measurement is done sequentially. The edge effects of the portable reflector will be discussed.

Development of a lab-sized antenna test range for millimeter waves
J. Saget (Electronique Serge Dassault), November 1989

In the last few years, the interest in millimeter wave systems, like radars, seekers and radiometers has increased rapidly. Though the size of narrow-beamwidth antennas in the 60-200 GHz range is limited to some 20 inches, an accurate far-field antenna test range would need to be very long. The achievement of precision antenna pattern measurements with a 70' or even longer transmission length requires the use of some power that is hardly available and expensive. A cost-effective and more accurate solution is to use a lab-sized compact range that presents several advantages over the classical so-called far-field anechoic chamber: - Small anechoic enclosure (2.5 x 1.2 x 1.2 meters) meaning low cost structure and very low investissement in absorbing material. No special air-conditioning is needed. This enclosure can be installed in the antenna laboratory or office. Due to the small size of the test range and antennas under test, installation, handling and operation are very easy. For spaceborne applications, where clean environment is requested, a small chamber is easier to keep free of dust than a large one. - The compact range is of the single, front fed, paraboloid reflector type, with serrated edges. The size and shape of the reflector and serrations have been determined by scaling a large compact range of ESD design, with several units of different size in operation. The focal length of 0.8 meter only accounts in the transmission path losses and the standard very low power millimeterwave signal generators are usable to perform precision measurements. The largest dimension of the reflector is 1 meter and this small size allows the use of an accurate machining process, leading to a very high surface accuracy at a reasonable cost. The aluminum alloy foundry used for the reflector is highly temperature stable. - Feeds are standard products, available from several millimeter wave components manufacturers. They are corrugated horns, with low sidelobes, constant and broad beamwidth over the full waveguide band and symmetrical patterns in E and H planes. - The compact range reflector, feeds and test positioner are installed on a single granite slab for mechanical and thermal stability, to avoid defocusing of the compact range. - A micro-positioner or a precision X Y phase probe can be installed at the center of the quiet zone. Due to their small size, these devices can be very accurate and stable. Due to the compactness of this test range, all the test instrumentation can be installed under the rigid floor of the enclosure and the length of the lossy RF (waveguide) connections never exceeds 1 meter.

Millimeter wave compact range measurements
M.J. Lynch (Harris Corporation), November 1989

This paper discusses the configuration and performance of millimeter-wave measurement systems comprised of standard Harris Shaped Compact Ranges, Hewlett Packard (HP) 8510B Network Analyzer, and Millitech frequency extenders designed for use with the network analyzer. Millimeter-wave capabilities have been integrated into the Harris automated measurement system to allow computer controlled millimeter-wave compact range characterizations. This system offers a new measurement alternative for antenna and Radar Cross Section (RCS) measurements. Measured 35 GHz data from the Harris Model 1606 compact range, and 95 GHz data from the Model 1603 compact range are included.

UHF performance results on a 1640 Harris compact range
M.J. Lynch (Harris Corporation), November 1989

This paper discusses the results of a recent study on the UHF performance of a Harris Shaped Compact Range. The design process for the dual polarized, 70% bandwidth UHF feedhorn is summarized. Measured data is presented for primary feedhorn patterns and for one-way CW field probe measurements with open-ended waveguide. The measured data is overlaid with computer predictions to validate the modelling tools and the measurement procedures. The automated quiet zone characterization procedure for amplitude and phase is also discussed.

Virtual vertex compact range reflectors
D.W. Hess (Scientific-Atlanta, Inc.),A.L. Wilcox (Scientific-Atlanta, Inc.), V. Farr (Scientific-Atlanta, Inc.), November 1989

In an earlier paper the virtual vertex compact range reflector was introduced and data from a specific design was reported. This paper describes the extension of the vertical vertex serrated edge concept to other reflectors that serve a wider range of application. Two new 12 ft focal length reflectors have been built that possess 3 ft and 6 ft diameter symmetric test zones. We describe the electromagnetic considerations and the mechanical design approach that has been used for these reflectors. We demonstrate the performance with field probe data showing the excellent surface accuracy of these units.

Imaging processing of bistatic scattered fields obtained in a compact range
T-H. Lee (The Ohio State University ElectroScience Laboratory),W.D. Burnside (The Ohio State University ElectroScience Laboratory), November 1989

An image processing method which uses the bistatic scattered fields of a target obtained in a compact range is presented in this paper. The transmitting and receiving antennas can be either two compact ranges or one compact range and a horn antenna. The compact range reflector can be either focussed or defocussed so that a near field situation can be simulated. The bistatic scattered fields are collected as a function of frequency and the angle of rotation of the target. Then they are processed coherently to determine the cross-range and down-range scattering centers of the target. Experimental results are presented to validate this image processing technique.

Scattering modulation of periodically rotating structures
A. Dominek (The Ohio State University),W. Lin (The Ohio State University), W.D. Burnside (The Ohio State University), November 1989

The scattering characteristics of a moving object are different than those of a stationary one. A common property of a moving object is the doppler frequency shift. For objects with rotating propeller blades, another property is the frequency shift from the periodic rotation of the propeller blades. This frequency shift is due to an amplitude modulation of the carrier frequency. Two techniques are presented involving the use of amplitude modulation. The first technique is for the observation of such modulation due to slowly rotating structures in a compact range. These results can be scaled to obtain results for this structure rotating at any speed. This is a great advantage since the model does not have to be designed to rotate propellers at high RPM's. The second technique utilizes the power spectrum density of the dynamic scattering signature of the rotating propellers to reduce undesirable clutter in the measurement.

Measurement of phased array patterns by near-field focusing
H.M. Aumann (Massachusetts Institute of Technology),F.G. Willwerth (Massachusetts Institute of Technology), November 1989

Performance verification of an adaptive array requires direct, real-time sampling of the antenna pattern. For a space-qualified array, measurements on a far-field range are impractical. A compact range offers a protected environment, but lacks a sufficiently wide field of view. Conventional near-field measurements can provide antenna patterns only indirectly. This paper shows how far-field antenna patterns can be obtained in a relatively small anechoic chamber by focusing a phased array in the near-field. The focusing technique is based on matching the nulls of far-field and near-field antenna patterns, and is applicable to conformal or nonuniform phased arrays containing active radiating elements with independent amplitude and phase control. The focusing technique was experimentally verified using a 32-element, linear, L-band array. Conventionally measured far-field and near-field patterns were compared with focused near-field patterns. Very good agreement in sidelobe levels and beamwidths was achieved.

Use of the music algorithm in the analysis of compact range field probe data
T.P. Delfeld (The Boeing Company),F.C. Delfeld (The Boeing Company), November 1989

The MUSIC (Multiple Signal Characterization) algorithm uses an eigenvector decomposition of measured data to classify signals in the presence of noise. It has been used for the angular classification of multiple radar signal emitters and ISAR imaging. Interest has grown in stray signal analysis in anechoic chambers. This paper will discuss the modification and use of the MUSIC algorithm for the decomposition of field probe data to angular spectrum. A brief discussion of the MUSIC algorithm theory will be presented. Modifications required for use in compact range angular spectrum analysis will be discussed in detail. Requirements on field probe measurements will be presented as well as their effects on the implementation of the algorithm. Both one way and two way measurements are considered for their relationship to the array manifold. Finally, some experimental validation generated on the Boeing range will be presented.







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