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A Compact test range for demonstrating antenna and RCS measurement performance
There are two main parts to an antenna or RCS measurement system: the measurement instrumentation, and the measurement environment or “range”. Performance of the measurement system is dependent upon both the instrumentation and the range. Developing a successful measurement system requires understanding both parts of the system. This paper describes a Compact Test Range that has been designed and built for the purpose of demonstrating antenna and RCS measurement performance of a complete measurement system. Additionally the Compact Test Range will serve as a development platform for future antenna and RCS products and systems. The purpose of the chamber, design objectives, design techniques, expected and measured performance are all discussed.
The New French anechoic chamber for wide band RCS measurements
Among its different facilities, C.E.A. has an indoor range for radar cross section (RCS) measurements over a wide frequency range from 0,1 GHz to 18 GHz. The dimensions of this anechoic chamber, 45m x 13m x 12m and a quiet zone diameter of about 3m, make it one of the largest in Europe. It consists in a parabolic reflector for frequencies higher than 0,8 GHz and a system using inverse synthetic aperture radar (ISAR) techniques for lower frequencies associated with a short pulse coherent radar instrumentation equipment. In addition to performant instrumentation and illumination systems, the main features of this installation dedicated to measure stealth objects, are low residual clutter, discrete target supports, and powerful processing software. The technical solutions adopted are described.
Amplitude accuracy of the PWS range probe
As the accuracy of antenna range instrumentation improves, multipath on the range is becoming the key limitation in antenna metrology. A fundamental requirement to improving range performance is the accurate and repeatable characterization of scattering on a range. A promising technique for range characterization is the planewave spectral (PWS) range probe. Earlier papers have demonstrated the ability of the PWS probe to locate multiple scattering centers on a range. Of equal importance to the user is the ability to correctly assess the magnitude of the scattering centers. This paper presents the problem of spectral peak broadening due to phase curvature from localized scatterers. Methods for improving the accuracy of scattering center estimation are presented along with numerical studies of the performance of these methods.
Practical considerations for millimeter wave antenna measurement instrumentation
As millimeter wave antenna systems become increasingly popular, engineers are challenged to develop effective methods for testing them. A practical method of designing a millimeter wave antenna measurement instrumentation system is presented in which frequency range, accuracy, dynamic range, and speed are considered.
A New calibration technique for bistatic RCS measurements
A bistatic calibration technique for wide-band, full-polarimetric instrumentation radars is presented in this paper. First general bistatic measurement problems are discussed, as there are the coordinate systems, the definition of polarization and the bistatic scattering behavior of convenient calibration targets. In chapter two the new calibration approach is presented. The general mathematical and physical description of errors introduced in the bistatic system is based on the radiation transfer matrix. The calibration procedure is discussed for the application with a vector network analyzer based instrumentation radar. For verification purposes measurements were performed on several targets.
Range instrumentation performance verification and traceability
This paper will discuss the need for performance verification, or calibration, of the transmitter and receiver systems used in an antenna or RCS range. Errors introduced by the range and positioning system means the instrumentation’s performance must be measured independently of the range and positioner. The performance verification should insure that the measurement system exceeds the manufactures’ specifications by a reasonable margin. The verification must be performed with the equipment installed on the range to insure adequate performance on the range. The system must als be verified as a system, rather than individual instruments. This guarantees that measurement errors in each instrument will not add together to exceed the system’s specifications. Testing of the system should be easy and repeatable to insure accuracy of the verification by the test technician. The tests should also be documented for later reference. The measurements should be traceable to a local standard such as NIST to certify the accuracy and stability of the measurement. The verification should be repeated on a regular basis to insure continued accuracy of the measurement system.
Measurement receiver error analysis for rapidly varying input signals
An assessment of instrumentation error sources and their respective contributions to overall accuracy is essential for optimizing an electromagnetic field measurement system. This study quantifies the effects of measurement receiver signal processing and the relationship to its transient response when performing measurements on rapidly varying input signals. These signals can be encountered from electronically steered phased arrays, from switched front end receive RF multiplexers, from rapid mechanical scanning, or from dual polarization switched source antennas. Numerical error models are presented with examples of accuracy degradation versus input signal dynamics and the type of receiver IF processing system that is used. Simulations of far field data show the effects on amplitude patterns for differing rate of change input conditions. Criteria are suggested which can establish a figure of merit for receivers measuring input signals with large time rates of change.
The Rafael radome measurement facility
The RAFAEL general purpose radome measurement range has been modernized and refurbished, maintaining its capability to accommodate all range of radome sizes up to 1.2 meters in diameter. It is based on a 3-axis positioner placed in an open anechoic chamber with a null seeker placed 20 meters away and about 10 meters above the ground. All the positioner’s axes are controlled by an automatic positioner controller. The receiver and source are based on a HP-8510B system. The X-Y null seeker serves for boresight error measurements. It has a 0.7m x 0.7m total motion span, which is about 2º. It is controlled by a dual-motor controller, so that the scanning antenna can be moved in any kind of motion. Instrumentation control and data acquisition and analysis is performed using a HP-330 UNIX controller. Present software handles monopulse antennas with or without a comparator, and can implement the comparator in software. There are two major measurement modes: One for BSE measurements and the other for radiation patterns.
The New compact test range at Dornier, Friedrichshafen
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.
A Plane-polar implementation of the plane-wave spectral range probe technique
The plane-wave spectral range probe technique introduced by Coblin can be used to locate multiple scattering centers on an antenna range. The x-y positioner presented by him is too costly for many applications. A plane-polar implementation of the technique provides a less costly alternative. A preliminary study of such an implementation is presented. The plane-polar positioner presented makes use of the roll-axis of a standard roll-over-azimuth positioner and the instrumentation of the range which was being used for this study.
Dynamic helicopter radar signatures
This paper addresses measurement and data processing techniques for dynamic helicopter radar signatures. Data products are presented and interpreted to highlight the utility of instrumentation radar systems as a means for determining radar scattering characteristics of objects with rotating components. Investigation of rotor-body multipath phenomena in helicopter imagery cannot sufficiently resolve ambiguities regarding ray traces that contribute to observed scattering events. The diagnostic insights gained from concurrent doppler spectral data aid in resolving these ambiguities. Unique spectral signatures resulting from rotor-body interactions are investigated, and a methodology is developed for diagnosis of the responsible scattering mechanisms. The results provide valuable insights into the radar spectral signatures o conventional helicopters.
Maestro - a mobile in-flight dynamic RCS system
The purpose of this paper is to present an overview of a turnkey mobile dynamic R.C.S. system, presently under design and development. The test system includes no less than 16 antennas, installed on two heavy duty tracking positioners, trailer mounted. The RF instrumentation is split over racks located on the positioners and in the mobile shelter housing the control equipment and operators and includes 14 receivers and 7 high power transmitters. The paper describes the antenna system, RF instrumentation, control and processing software as wek as operational and modularity aspects of this dynamic RCS facility.
Techniques for RCS quality control measurements in unimproved environments
Measuring the radar cross section of low-observable (LO) vehicles require an RCS quality control (QC) program that will last throughout the life cycle of the vehicle, from component production to operational deployment and depot maintenance. Testing must be done at regular intervals to ensure that surface or sub-surface damage has not degraded the RCS characteristics of the vehicle beyond acceptable limits. In the past, these measurements were complicated by the requirement for and expensive, well-prepared RF test environment. The test range—usually a fixed site—is often remotely controlled. System Planning Corporation (SPC) has developed an RCS QC measurement technique that requires little or no facility improvements while offering high sensitivity inverse synthetic aperture radar (ISAR) images. The instrumentation radar system can be located at the production, maintenance, or operational site of the vehicle or component. As a result, the QC program is both economical and reliable.
VHF/UHF indoor RCS measurements using a tapered or compact range
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.
Instrumentation: more speed!
Data collection is increasingly becoming the limiting factor in overall antenna and RCS measurement time. An equation for data collection time for multiple parameter measurements is presented along with and ordering function for determining the optimum nesting order for parameters. An example is used to demonstrate measurement speed enhancement techniques, reducing data collection time by 65 percent. Changing from stepped to linear near-field scanning reduced collection time by 75 percent.
Measurement Techniques for Active Antenna Systems Using Broadband Waveforms
Generally, the radiating properties of passive antennas can be measured with CW test signals in either transmit or receive mode with identical results. For a variety of practical reasons, outdoor antenna ranges have traditionally been configured to receive on the antenna under test. A growing class of active antennas, however, are non-reciprocal as systems and must be tested independently in both transmit mode and in receive mode. Often, broadband (non-CW) test signals must be utilized in the testing of these systems. In this paper, antenna range configurations are compared and practical instrumentation techniques for measurement of broadband signals on the antenna range are discussed. A Rome Laboratory pulse antenna measurement receiver, designed to obtain complex time domain profiles of transmitted waveforms as a function of angle, will also be described.
An Instrumentation radar system for use in dynamic signature measurements
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.
Validation testing of the planar near-field range facility at SPAR Aerospace Limited
A series of measurements to validate the performance of a Planar Near-Field (PNF) Antenna Test Range located at the Satellite and Aerospace Systems Division at Spar Aerospace Limited were made by Scientific-Atlanta during the month of February 1992. These measurements were made as a part of a contract to provide Spar with a Model 2095 Microwave Measurement System with planar near-field software options and related instrumentation and hardware. The range validation consisted of a series of self-tests and far-field pattern comparison tests using a planar array antenna provided by Spar that had been independently calibrated at another range facility. This paper describes the range validation tests and presents some of the results. Comparisons of far-field patterns measured on the validation antenna at both the Spar PNF facility and another antenna range are presented.
The Commissioning of a fast planar near-field facility
Some of the novel mechanical and electronic subsystems features on a recently installed high specification planar near-field scanner are described together with a discussion of the problems encountered during the commissioning period. The test facility incorporates a number of novel design concepts both in terms of its instrumentation, control and processing subsystems. Features of the facility are the speed of data acquisition and the accuracy of the acquired near-field data. Scan speeds of up to 0.8 m/s and positional accuracies of 30 microns in the Z-axis have been achieved, and the near-field data is acquired, displayed and measured on the fly, hence allowing a typical 3m x 3m scan to be executed and the measured near-field results to be displayed and processed within a period of thirty minutes.
Remote thickness sensor
Applications that require tight tolerances on dielectric thickness control need accurate sensors. A technique has been developed that will allow for the measurement of thickness without requiring surface contact. High resolution radar imaging, commonly used in RCS measurements , is now being used to measure thickness. Electromagnetic fields reflected from the front and rear surface are detected and the time response delta is converted into thickness. A major advantage of this method is that it is not affected by varying sensor offset height.
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