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Traditional Compact Range Antenna (CRA) applications are related to Antenna Pattern and RCS measurements. For these purposes, as a rule, CRA are installed within or outside of an anechoic chamber as stationary equipment. However, for some modern applications, such as Electronic Warfare development, radar tracking system testing, indoor RF environment simulation and others, where dynamic and pointing properties of an AUT are to be tested, the mobile and multi-beam CRA is of great importance, since it provides the designer with powerful simulation and testing capabilities. Such a CRA has been designed, built and tested at ORBIT ADVANCED TECHNOLOGIES, LTD. The design trade-offs, CRA analysis, test set-up and results are discussed in the presented paper.
A technique is presented for synthesizing a uniform plane wave at Fresnel zone distances. The method attempts to bridge the gap between compact range techniques and far field techniques, in the sense that one may potentially perform antenna or scattering measurements when a compact range reflector is electrically too small and the available far field range length is also too small. Similar to a far-field range, the distance to the test zone region generally varies with the side D of the test item and the frequency of operation being proportional to D2/X. Similar to a compact range, the test zone is confined to a localized region, and the quality of the test zone field does not improve with distance as it does for a far field range. The method is implemented by compensating the phase taper associated with a single radiator by employing a uniformly excited, concentric ring array. The quality and transverse extent of the test zone fields may be adjusted by varying the relative amplitude and phase excitation of the array. Syntheses of a test zone region characterized by a 1 dB amplitude ripple over 70% of the disk defined by the projected ring aperture is demonstrated.
A small compact range measurement facility has been installed at the Environmental Research Institute of Michigan (ERIM) for research aimed at improving RCS measurement and radar imaging techniques. This paper describes the facility, which is referred to as the Experimental Range Facility (ERF). The ERF has two instrumentation radars; a Flam & Russell FR959 gated CW radar and a Hughes MMS-300 pulsed radar. The radars are connected to a suite of workstations, which support a variety of internally and externally developed radar imaging and data exploitation software. The ERF is also equipped with sophisticated target positioning control and sensing equipment.
Lockheed Sanders, Inc., has constructed a state-of-the-art electromagnetic measurement system. Cost considerations dictated the use of existing facilities and space, We took advantage of the lessons learned from the Lockheed Advanced Development Company's (LADC) Rye Canyon, California Facility [1]. Lockheed Sanders, Inc. now has a complete indoor measurement capability from VHF to MMW. Lockheed Sanders, Inc. needed a facility capable of making measurements over a broad range of frequencies. The system consists of a tapered chamber and a compact range. The system consists of a tapered chamber and a compact range. The tapered chamber has a measurement area of 28' x 28' x 34'. This range is capable of antenna and RCS measurements from .1 to 2 GHz. The compact range is designed for 2 to 40 GHz. Using a Scientific Atlanta, Inc. reflector scaled from the Rye Canyon reflector, a 6' x 6' quiet zone is possible. Feeds consist of a feed cluster aligned for phase and limiting parallax and horn cross-talk. Both chambers use the Flam and Russell 959 measurement system. This paper will discuss the chambers and their operation. The paper will close with a demonstration with measurements on standard, complex targets.
DASA's high precision Compact Range Program, which already was a breakthrough in new dimensions of RF measurements standards, will not be completed by a revolutionary new and one of the world's most unique types of Cylindrical Outdoor Near-Field Test Range. The most striking component of this new type facility will be its dominating fully air-conditioned, up to 50 m high diamond shaped concrete tower which is the integral part of the vertical probe scanner subsystem. Although this test range is located outdoor, it allows extremely precise characterization of all typical parameters for state of the art antenna systems.
The plane wave quality of a compact range (CR) is usually specified in terms of the crosspolar level and the magnitude and phase ripple in the test zone. The way these deviations from the ideal plane wave affect the measurement of different antenna types can be treated by the application of the reciprocity principle between the transmitting and receiving antenna in a measurement set-up. By the application of the sampling theorem, it is found that the measured antenna pattern can be expressed as a summation of the plane wave spectrum components of the field at the test zone weighted by the true radiation pattern of the antenna under test (AUT) evaluated at the CR plane wave directions in the rotated coordinate system of the AUT. The inverse procedure can be used to extract the CR plane wave information (and therefore the CR field at the test zone by means of the Fourier series) from the measurement of a standard antenna with a known radiation pattern.
To gain greater insight into the design of surface ships with reduced radar cross-section characteristics, a structure resembling a ship deckhouse was physically modeled and measured. The structure was represented as a truncated pyramid. Four scaled pyramids were fabricated, all identical except for the radii of the four vertical (slanted) edges. The pyramids were measured at the University of Massachusetts, Lowell Research Foundation, submillimeter laser compact range. Measurements were made a scaled X-band using a laser-based system that operates at 585 GHz with the pyramids scaled at a ratio of 1:58.5. These shaper were measured at 0.75 degrees depression angles on a smooth metal ground plane at both HH and VV polarizations. The goal of this study was to determine if small changes in the radius of the curvature of the slanted edges could significantly affect the radar cross-section of the pyramid. In this paper the results of measurements of the pyramids will be presented. The data are compared with computer code predictions and the differences are discussed.
The Hughes Aircraft Company Compact Range facility for antenna and RCS measurements, scheduled for completion in 1993, is described. The facility features two compact ranges. Chamber 1 was designed for a 4 to 6 foot quiet zone, and Chamber 2 was designed for a 10 to 14 foot quiet zone. Each chamber is TEMPEST shielded with 1/4 inch welded steel panels to meet NSA standard 65-6 for RF isolation greater than 100 dB up to 100 GHz, with personnel access through double inter locked Huntley RFI/EMI sliding pneumatic doors certified to maintain 100 dB isolation. While Chamber 1 is designed to operate in the frequency range from 2 to 100 GHz, Chamber 2 is designed for the 1 to 100 GHz region. Both RCS measurements and antenna field patterns/gain measurements can be made in each chamber. The reflectors used are the March Microwave Dual Parabolic Cylindrical Reflector System with the sub-reflector mounted on the ceiling to permit horizontal target cuts to be measured in the symmetrical plane of the reflector system.
RCS measurement accuracy is degraded by reflections occurring between the feed antenna, the range, and the radar subsystem. These reflections produce errors which appear in the image domain (both 1-D and 2-D). The errors are proportional to the RCS magnitude of the target under test and they are present in each of the typical range calibration measurements. Current 2-term error models do not predict or account for the above errors. An improved 8-term error model is developed to do so. The model is based on measurable reflections and losses within the range, the feed antenna, and the radar. By combining the improved error model with the commonly used 2-term RCS range calibration equation, we are able to quantify the residual RCS errors. The improved error model is validated with measured results on a direct illumination range and is used to develop specific techniques which can improve RCS measurement accuracy.
The proposed synthesis method allows the calculation of the diffraction figure in the focal plane of the compact range, starting from a field distribution in linear polarization over a plane in the Fresnel zone. Applying this method (in only one dimension) to the ideal near field of a FFOC compact range, a linear array is synthesized which can be extrapolated to a planar array feeder design; providing excellent features in the quite zone.
The Georgia Tech Research Institute has designed and built a field probe for the U.S. Army Electronic Proving Ground Compact Range. The field probe is an R-0 scanner covering a 59-foot diameter area. It includes a laser-referenced Z-axis correction servomechanism, a polarization positioner, and a cable handling system for one-way data acquisition.
This paper describes a calibration technique for reducing the errors due to mismatch between the measurement receiver and the antenna in microwave antenna relative gain measurements. In addition, this technique provides an accurate method for measuring the input return loss of the antenna under test. In this technique, a microwave reflectometer is mounted between the measurement receiver and the antenna test port. The reflectometer is calibrated and used to measure the return loss of both the test and calibration antennas. Using this information in conjunction with the HP 8530A antenna gain calibration, the corrected gain of the antenna under test is computed. Compact range antenna measurements verifying the calibration model and error analysis are presented. Practical implementation considerations are discussed.
A full RCS calibration technique using a dihedral corner reflector is presented in this paper. This scheme is valid for monostatic configuration and characterized by three aspects: (1) the frequency responses of four measurement channels can be mutually independent and thus, no special care has to be taken for signal paths; (2) only scattering matrix measurements of the dihedral at two orientations about the line-of-sight direction are needed since the transmitter and receiver are related through the reciprocity theorem; and (3) simple and useful expressions are used to solve for the calibration parameters. This technique is verified by several 2-18 GHz wideband RCS measurements performed in the OSU/ESL compact range.
The applications of conventional reflector type compact antenna test ranges (CATR), becomes increasingly difficult above 100 GHz. The main problems are the tight surface accuracy requirements for the reflector, and therefore the high manufacturing costs. These problems can be overcome by the use of a new hologram type of compact range, in which a planar hologram structure is used as a collimating element. This new idea is described, and its performance is studied with theoretical analyses and measurements at 110 GHz.
This paper addresses measurement requirements for space communication antennas and identifies antenna parameters most influenced by indoor compact range quiet zone quality. These parameters include sidelobe level, beam pointing, and gain. The compact range mechanisms limiting measurement accuracy are identified and discussed. Proven methods for characterizing quiet zone performance are described and demonstrated through illustration and example. Analysis is presented which related quiet zone quality characteristics to antenna measurement accuracy. The paper summarizes typical measurement results and error levels achievable for modern compact range systems. Methods for improving compact range performance for satellite antenna testing are also presented.
A method to estimate the rms error in the compact range reflector surface is presented. The method uses the target zone field of the reflector and is based on the fact that the random errors in the reflector surface cause energy to subtract from the main beam resulting in reduction of the axial gain. The reduction in the axial gain can be used to estimate the rms error. It is shown that if the target zone fields of the reflector are probed at high frequencies such that the irregularities in the reflector surface are the main source of error in the target zone fields, then the proposed technique gives a good estimate of the rms error in the reflector surface.
Implementation of a two-ring array for feeing a compact range reflector is investigated. The array is designed to produce a shaped beam with a null at the angle corresponding to the rim of a circular-aperture offset paraboloid. Therefore fields diffracted from the reflector rim are reduced and no reflector edge treatment is necessary. The advantages and disadvantages associated with various feed systems are discussed. A dielectric-filled radial transmission line is proposed as a simple, cost effective implementation of the array beam-forming network. Curves for determining the required dielectric constant for null placement at a desired angle are presented. System bandwidth is examined. Methods for impedance matching and suppression of higher order modes in the beam-forming network are proposed.
This paper presents a study of (Broadband) feeds for a large compact range. Single feeds would be used for an octave or more, in place of 1/2 octave feeds. The study indicates improvement from mounting broadband feeds closer to the subreflector. The McDonnell Douglas Technologies Inc. (MDTI) large compact range uses a Harris 1630 system. The Harris system employs 1/2 octave feedbands. This creates limits for certain measurements. Requirements of the collimator system include fairly constant, relatively high gain feeds (Narrow beamwidth over a broad frequency range.) MDTI made initial studies of various broadband feeds. This study used an AN10F, borrowed from the vendor (GTE Government Systems). The AN10F approximates the required characteristics at its upper frequency range, (upper X - Ku Band). Field probe data taken with the feed installed near the focus of the sub reflector of the Harris collimator confirmed excessive amplitude taper below Ku Band. Further study illustrates the possibility of improved performance with the feed positioned nearer the Sub reflector. (Defocussed)
Increasing use is being made of millimeter-wave systems and there is a need for improved antenna measurement facilities operating at these higher frequencies. Although the practical implementation of compact range and near-field/far-field techniques becomes increasingly difficult, by using a hybrid approach, the attributes of these existing schemes can be exploited and their limitations overcome. The technique uses a linear near-field probe to carry out an instantaneous integration of the field in the date acquisition requirement, together with a quasi-real-time prediction capability. This contribution reviews a number of implementation schemes for the semi-compact antenna test range (SCATR) approach which have been investigated over the past decade and presents the latest results. An implementation of the SCATR with amplitude-only data is presented as an economical and viable method for millimeter-wave frequencies.
A 4 foot by 4 foot near field planar scanner is used to evaluate the performance of a SA5751 compact range in CSIST. Using the far field patterns integrated from the scanned aperture fields, the coming directions of the clutters in the chamber can be determined. Often the clutter level is less than the side lobe level of the far field pattern, the scanned field is multiplied by a certain weighting function before integration to pop out the clutter signal. However the weighting method would broaden the main beam and hence clutters coming close along the reflected wave of the reflector are still can not be seen (sic). In this article, a method called main beam suppression, subtracting a constant filed (sic) on the scanned aperture, is introduced to solve this kind of problem and the result shows it serves well for finding those clutters hidden by the main beam and the side lobes nearer to it.