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Instrumentation
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.
Diagnostic imaging of targets with rotating structures
A Bati (Pacific Missile Test Center),D. Mensa (Pacific Missile Test Center), G. Fliss (Pacific Missile Test Center), R. Dezellem (Pacific Missile Test Center), R. Siefker (General Motors), November 1989
RCS instrumentation systems capable of combining wide-band and ISAR techniques to obtain two-dimensional images are widely used to perform RCS diagnostic and measurement functions. Objects involving rotating structures, such as blades of propulsion systems complicate the diagnostic task. The paper address the utilization of diagnostic RCS systems to meaningfully determine the radar signatures of objects with rotating components and presents results obtained from a generic data set, typically available from wide-band RCS instrumentation systems. The results provide valuable insight to the signature of objects with rotating components.
Performance comparison - gated-C.W. and pulsed-I.F. instrumentation radars
B.W. Deats (Flam & Russell, Inc.), November 1989
This paper examines the primary differences between gated-c.w. and pulsed-i.f. instrumentation radar systems. Following a brief explanation of the fundamental theory behind each radar type, a performance trade study is presented. The impact of i.f. bandwidth on the operation and performance of the radar is presented by first briefly describing the major similarities and differences between the two radar types and the resulting impacts on performance. Differences in the gate performance, sensitivity, dynamic range, speed, and accuracy are summarized. To show the performance advantages and shortfalls of each radar type, benchmark test scenarios are presented. The resulting summary can be used as a guide in determining the optimal radar type for a specific range geometry and measurement requirement.
High speed, multi frequency measurements
O.M. Caldwell (Scientific-Atlanta, Inc.), November 1989
Precise and complete measurements of advanced electromagnetic systems demand dramatically higher data acquisition speeds than those commonly attainable. Specific challenges include requirements for wideband measurements with arbitrarily spaced frequency steps. These types of measurements are often encountered in characterizing EW/ECM systems, radars, communications systems, and in performing antenna and RCS measurements. The Scientific-Atlanta Model 1795 Microwave Receiver offers capabilities directly applicable to solving measurement problems posed by highly frequency agile systems. These problems include: 1) timing constraints 2) data throughput 3) RF interfacing 4) maintaining high accuracy A technique is discussed which shows the application of the Model 1795 Microwave Receiver in its high frequency agility mode of operation. Measurement examples are presented showing the advantages gained compared to previous methods and instrumentation configurations.
Special electromagnetic interference vulnerability assessment facility (SEMIVAF)
J.G. Reza (SLCVA-TAC), November 1989
The Vulnerability Assessment Laboratory (VAL) anechoic chamber at White Sands Missile Range, New Mexico was reconfigured and refurbished during the last part of 1988. This paper will be a facility description of the state-of-the-art Special Electromagnetic Interference (SEMI) investigation facility. Electromagnetic susceptibility and vulnerability investigations of US and, in some cases, foreign weapon systems are conducted by the EW experts in the Technology and Advanced Concepts (TAC) Division of VAL. EMI investigations have recently been completed on both the UH-50A BLACKHAWK and AH-64A Apache helicopters in the chamber. The paper will cover the facility's three anechoic chambers, shielded RF instrumentation bay, computer facilities for EM coupling analyses, and the myriad of antenna, antenna pattern measurement, amplifier, electronic, and support instrumentation equipment for the chambers. A radar cross section measurement and an off-line RCS data processing station are also included in the facility.
Requirements for accurate in-flight pattern testing
C.H. Tang (MITRE Corporation), November 1989
The purpose of this paper is to discuss the accuracy requirement of a generic measurement system for in-flight antenna pattern evaluations. Elements of the measurement technique will be described. An attempt is made to distinguish the measurement requirement for a narrow beam radar antenna in contrast to that for broad beam communication antennas. Major elements of the measurement technique discussed include the flight path geometry, the multipath propagation problem, and the measurement errors. Instrumentation requirements consist of the ground segment, the receive and the tracking subsystems, and the airborne equipment, the radar components and the navigation and attitude sensors. Considering the in-flight antenna pattern testing as a generalized antenna range measurement problem, various sources of measurement errors are identified. An error budget assumption is made on each error component to estimate the overall expected accuracy of the in-flight antenna pattern measurement.
Aramis - a flexible near-field antenna test facility
O. Silvy (Electronique Serge Dassault), November 1989
A flexible near-field antenna test-facility is presented. This system gathers all that is necessary to design, to debug and to validate the high performance antennas which are made by ESD. ARAMIS has been operational since January 1988. Its applications are: - Near-field measurements (for diagrams): * planar, * cylindrical. - High speed field mapping (for default analysis): * planar radiating surface, * cylindrical radiating surface. - Generation of element excitation (active phased array testing): * planar antennas, * cylindrical antennas. - Direct far-field measurements (probes, small antennas), - Circuit measurement (S parameter). The facility features a specially designed scanner. Thanks to its six degrees of freedom, this positionner allows the differents types of measurements to be made. The instrumentation is based upon the HP 8510 B network analyzer. A single computer performs the measurements, transforms the data and presents the graphics (linear diagrams, color maps, three-dimensional colored projections). In order to grant a high scan speed, the system uses the FAST CW mode of the HP 8510 B. An external trigger is provided during the motion process of the probe. A rate of 500 measurements/sec. has been proved. This on-the-fly process is clearly depicted. Experimental results are presented which include: - Low sidelobe (-38 dB) antenna diagrams. - Default analysis through: * Amplitude mapping (leakage short-circuit in a microstrip antenna). * Phase mapping (out-of band comparison between two radiating element technologies). * Measurement of excitation laws. * 3-D transformation. - Simultaneous on-the-fly acquisition of up to three antenna outputs.
Automated millimeter wave evaluation system for advanced materials and frequency selective surfaces
W.S. Arceneaux (Martin Marietta Electronics & Missiles Group), November 1989
An automated instrumentation system has been configured for the purpose of evaluating advanced composites, radar absorbing materials, and frequency selective surfaces (FSS) in free space. Electrical test frequencies are divided into three bands that range from 18 to 60 GHz for any linear polarization. Software has been incorporated to calculate dielectric properties from the measured transmission and reflection characteristics. Using the HP9836 computer, software was written to automate and integrate the Anorad 3253 positioner with the HP8510 network analyzer. This system allows for the input of up to five incident angles at vertical, horizontal, and cross polarization. The measured transmission loss (amplitude and phase) at multiple incident angles is then plotted for comparison. This paper gives a complete description of the system configuration, calibration techniques, and samples of output data. Material properties are computed and compared to specified and theoretical values. Measured results of an FSS structure are compared to its predicted response.
VHF/UHF RCS measurements in indoor microwave facility
J. Saget (Dassault Electronique),J. Garat (CEA/CESTA), November 1990
Radar cross section (RCS) measurements were performed in the 0.1-1 GHz band in an anechoic chamber optimized for microwave frequencies. Selection of proper instrumentation, antennas, measurement techniques and processing software are discussed. Experimental results, showing the accuracy and sensibility of the system are presented.
Evaluation of adaptive multiple beam antennas
R.B. Dybdal (The Aerospace Corporation),K.M. Soohoo (The Aerospace Corporation), November 1990
Adaptive antenna systems will expand the test requirements for conventional antenna testing. The specific example of adaptive uplink antennas for satellite communications illustrates this required expansion. Test facilities will require additional capabilities to generate both desired and interference test signals with differing arrival directions. A novel extension of compact range technology is described for testing spaceborne designs. Instrumentation likewise will require further development for testing wide bandwidth adaptive cancellation designs used with spread spectrum modems.
An HP-8510-based 45-GHz instrumentation radar for ISAR image and glint studies
R. Dinger (Naval Weapons Center),D.J. Banks (Naval Weapons Center), D.R. Gagnon (Naval Weapons Center), E. Van Bronkhorst (Naval Weapons Center), November 1990
A 45 GHz instrumentation radar system unique in several respects has been developed for inverse synthetic aperture radar (ISAR) and tracking angle scintillation (glint) studies. The system, based on a Hewlett-Packard HP-8510B network analyzer, is fully polarimetric and operates on a 1000-m outdoor far-field range. An amplitude monopulse receiver provides a measure of the instantaneous apparent-center-of-scattering of the target. Successful glint and ISAR measurements have been made on targets as large as 8 m.
Correction/calibration of wide-band RCS radar data containing I/Q error
D.E. Pasquan (Texas Instruments Incorporated), November 1990
In-phase and quadrature (I/Q) aberrations in radar receiver data create problems in radars used for radar cross section (RCS) measurements. I/Q errors cause incorrect representations of the target under test. A method for correcting I/Q error and calibrating the measured amplitude to a scattering standard provides a means of obtaining a more accurate representation of the target under test. The RCS measurement instrumentation addressed here uses a wide band receiver with a single quadrature mixer for conversion of radio frequency (RF) to base band (also referred to as video) frequency. In the one-step down conversion, distortions in the I/Q constellation occur, causing I/Q errors. This method quantifies the extent of the I/Q problem by estimating the actual I/Q error from a series of calibration measurements. An algorithm is presented which quantifies parameters of the I/Q distortion, then uses the distortion parameters to remove the I/Q aberrations from the target measurement.
The Effects of non-systematic instrumentation errors on measurement uncertainty
O.M. Caldwell (Scientific-Atlanta, Inc.), November 1990
The effects of non-systematic receiver instrumentation errors on precision antenna measurements are investigated. A simple uncertainty model relating dynamic range to random perturbation effects on amplitude measurements is proposed. Examples of measurement uncertainty versus both input level and measurement speed are presented using data taken on modern measurement receivers. Dara are compared with the model to estimate measurement uncertainty at various pattern levels and acquisition speeds. Equivalent dynamic range specifications are deduced from the measures data.
Short term stability performance of pulsed instrumentation radars using TWTAS
J. Allison (Hughes Aircraft Company),J. Paul (Hughes Aircraft Company), R. Santos (Hughes Aircraft Company), November 1990
Pulse-to-pulse amplitude and phase noise can affect the overall measurement accuracy of RCS instrumentation radars. Depending upon the measurement requirements, such noise can limit the overall performance whenever pulse-to-pulse repeatability is required in the signal processing. Radar systems using pulsed TWTAs are subject to high noise due to limitations in the performance of the TWTA modulators and power supplies. A characterization of this additive noise is important to understand the limitations in system performance. Measurements have been made on kilowatt power TWTAs at L and X band as well as 20 watt pulsed TWTAs at S, C, and X/Ku band at various duty cycles and PRFs.
Global and local features of wideband RCS signatures
A. Bati (Pacific Missile Test Center),D. Mensa (Pacific Missile Test Center), R. Dezellem (Pacific Missile Test Center), November 1990
The utility of wideband RCS data for characterizing scattering mechanisms of complex objects has been established by wide-spread applications. The fundamental data from which the final products are derived consist of calibrated scattered fields measured coherently as a function of frequency and aspect angle. By processing these data, one-dimensional range or cross-range reflectivity profiles can be derived; by further processing, two-dimensional images can be derived. Modern RCS instrumentation systems capable of rapidly measuring and processing wideband data provide more object information than is conveyed by the RCS pattern, which has been the traditional descriptor of scattering behavior. The procedures of one- or two-dimensional imaging inherently involve integration processes, constituting many-to-one mappings in which data from a large set are collapsed to produce an individual pixel of the image. For example, a particular pixel of a range response is derived from the total object response “integrated” over a band of frequencies; similarly, a pixel of a two-dimensional image is derived from the object response “integrated” over frequency and angle. The exposure of a local feature of the object signature, obtained by collapsing the fundamental data, comes at the cost of obscuring the global descriptor. This paper explores techniques for presenting large amounts of information on single displays which retain both global and local features of the scattering process. These tools provide to the RCS analyst options for extracting and interpreting significant information from the measured data without arbitrary degrees of integration which can mask essential details represented in the data. The display methods utilize color coding to increase the amount of information conveyed by a single plot. Because color reproduction is not available for the proceedings, the paper is to be distributed at the conference.
Applications of superworkstations in compact range measurements and processing
H. Shamansky (The ElectroScience Laboratory),G. Hall (Tektonix Incorporated), S. McCowan (Tektonix Incorporated), W. Allen (The ElectroScience Laboratory), W. Lin (The ElectroScience Laboratory), November 1990
As the advances in silicon technology continue to redefine the realm of “practical” for scientists and engineers, traditional techniques for acquiring measurements and processing the exceedingly large data sets generated must be constantly improved, and often times discarded as new concepts replace them. The new class of SuperWorkstations available today provides a convenient means to not only maximize the performance of the compact range instrumentation, but also suggests entirely new techniques and algorithms in data acquisition, storage, processing and interpretation. In considering these advances available through SuperWorkstations, benefits in the area of measurement data acquisition and local storage are detailed, recent improvements in magnetic and visual storage techniques and their application to data archiving are considered, new and unique techniques for scattering center identification in near real time are presented, and finally a discussion of tomorrow’s computer technology and the further impact on the compact range completes the study. This paper examines the efforts currently underway to exploit one such superworkstation, the Tektronix XD88, in the compact range at the ElectroScience Laboratory. In the effort to effectively utilize the superworkstation, many disciplines are coupled together (hardware, software, graphics, video presentation, among others) to augment each other. It is this multidiscipline coupling that will serve to expand the realm and utility of SuperWorkstations in the compact range, and the goal of this brief introduction is to present some aspects of these varied areas to the reader, hopefully motivating the reader to consider further extensions of SuperWorkstations.
High speed control of instrumentation for antenna and RCS measurements
R.J. Juels (Comstron Division of Aeroflex Laboratories),Y. Lissack (Comstron Division of Aeroflex Laboratories), November 1990
Today’s measurement systems are placing ever increasing demands upon the computer systems which control instrumentation and collect data. This paper investigates high speed control of instrumentation for RCS and antenna measurements. Off-loading of I/O from control and data acquisition computers is examined with a view toward improving measurement throughput and simplifying I/O control tasks. These methods are particularly important for multi-tasking systems and networked resources where high speed real time control is burdensome. Attributes of I/O enhancement architectures are examined and tradeoffs between performance and flexibility are reviewed.
Gregorian compact range analysis and design
J. Molina (IRSA),J.A. Rodrigo (IRSA), J.L. Besada (Polytechnic University of Madrid), M. Calvo (Polytechnic University of Madrid), November 1990
This paper deals with design and evaluation of Compact Range Antenna and RCS measurement systems. Reflector subsystem and feeders design as well as quiet zone evaluation and system performance qualification are considered. Acquisition, process and presentation software to control the whole system has been developed and successfully implemented. Two systems have been designed and are now at implementation stage. A Gregorian concept Compact Range is now been constructed at RYMSA (Spain). This facility has been fully designed by IRSA and will be operative by the end of 1990. Compact Payload Test Range (CPTR) at ESTEC (ESA) is now been tested. System Instrumentation and PAMAS (Payload and Antenna Measurement and Analysis Software) have been developed.
An Overview of parameters determining productivity and sensitivity in RCS measurement facilities
E. Hart (Scientific-Atlanta, Inc.),W.G. Luehrs (Scientific-Atlanta, Inc.), November 1990
A major objective in the design of an RCS measurement facility is to obtain the greatest possible productivity (overall measurement efficiency) while maintaining the accuracy and sensitivity necessary for low radar cross section targets. This paper will present parameters affecting the total throughput rates of an indoor facility including instrumentation, target handling, and band changes-one of the most time consuming activities in the measurement process. Sensitivity and accuracy issues to be discussed include radar capabilities, feeds and feed clustering, compact range, background levels, and diffraction control.
Hughes Aircraft Company's new RCS measurement facility
A.R. Lamb (Hughes Aircraft Company),R.G. Immell (Denmar, Inc.), November 1990
The Hughes Aircraft Company recently completed the design, development, and construction of a new engineering facility that is dedicated to providing state-of-the-art Radar Cross Section Measurements. The facility is located at the Radar Systems Group in El Segundo, California and consists of two secure, tempest shielded anechoic chambers, a secure high bay work area, two large secure storage vaults, a secure tempest computer facility, a secure conference room, and the normal building support facilities. This RCS measurement test facility is the result of Hughes committing the time and money to study the problems which influence user friendly RCS measurement facility design decisions. Both anechoic chambers contain compact ranges and RCS measurement data collection systems. A description of the facility layout, instrumentation, target handling capability, and target access is presented.


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